Vo l. 33. N o . 280. Ap r i l 1947
TH E INSTITUTE OF PETROLEUM.
A m eeting of th e In s titu te of Petroleum was held a t Manson House, P o rtlan d Place, London, W .l, on W ednesday, J a n u a ry 8, 1947. L ie u t.- Colonel S. J . M. Auld, P a st-P re sid en t, was in th e Chair.
Th e Ch airm an, opening th e m eeting, said : The paper before us to -n ig h t is of considerable im portance. I t is indicative of tw o th in g s ; first, of the w ay in which petroleum is tak in g its place in world economy, quite a p a rt from its use as fuels and lu b ric a n ts; and, secondly, th e very great a tte n tio n we are beginning to realize m u st be paid to soil and p lan t pathology if our efforts, a t th e present tim e of such im portance, a re -to be successful in m aking tw o blades of grass to grow where only one grew before.
Mr. Leyland Cole presented th e following paper, which he illu strated by m eans of a cinem atograph sound film giving a general im pression of th e process of spraying for p la n t protection, th e dam age caused by some of the b etter know n insects and fungi, an d tests to indicate th e effectiveness of various insecticides.
PETROLEUM PRODUCTS IN AGRICULTURE: THE ROLE OE PETROLEUM IN PLANT PROTECTION.
B y L. W. Leyland Co le, M.Sc., B.Sc.(Agric.), F .R .I.C .*
Su m m a r y.
T he im m ense loss o f food crops, d u e to w eed c o m p e titio n a n d to th e a c tiv ity o f in sects a n d fu n g i in th e field a n d in th e w arehouse, is bein g red u ced b y th e d ev elo p m en t o f n ew a n d m ore effective m eth o d s o f p la n t p ro tectio n .
P e tro le u m oil h a s b e en u se d for a long tim e in th e fo rm o f o il-w a te r em ulsions fo r a p p lic atio n to decid u o u s a n d to c itru s fru it, an d in re ce n t y e ars chem icals d eriv ed fro m p e tro le u m h a v e fo u n d m a n y a p p lic atio n s in a g ric u ltu ra l p e s t co n tro l. T h e b ase oils o f h o rtic u ltu ra l sp ra y s h a v e c e rta in a ccep ted ch ara cte ristics, b u t m o re w ork b y th e b iochem ist a n d p la n t p h y sio logist is re q u ire d befo re th e p e rfe c t s p ra y oil c an b e evolved. I n p ractice , d ilu te oil em u lsio n s o f v a rio u s ty p e s a re sp ra y ed on th e tre e b o th in w in ter a n d in su m m er, care b ein g ta k e n to com bine m ax im u m in secticid al effect w ith m in im u m p h y to to x ic ity . O il is a n ex ce llen t insecticide in its e lf b u t i t is also a n im p o rta n t c a rrie r fo r o th e r in secticides a n d fo r fungicides. C ertain p e tro leu m frac tio n s possess w eed-killing p ro p e rtie s a n d a re useful b o th as selective a n d n o n -selectiv e herbicides. I m p o r ta n t chem icals d eriv ed from p e tro leu m a n d u sed in p e st c o n tro l a re e ster salts, m eth a lly l chloride, and a m ix tu re o f d ich lo ro p ro p en e a n d d ich lo ro p ro p an e (D -D ), th e l a tte r bein g a v e ry successful soil fu m ig a n t.
In trodu ctio n.
Th e disruption an d disorganization of w ar have twice in this tw entieth century bro u g h t vividly to th e forefront th e basic im portance of food production a n d distrib u tio n and, even in th e relatively easy days of peace, w hen m ost people ta k e th e ir food supply for granted, more th a n h a lf m an
Q
* Shell P e tro le u m C om pany, L td .
2 0 4 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
kin d —over 10 0 0 million people— suffer from m a ln u tritio n , often to a n e x te n t which affects h ealth , reproduction, an d life itself. I t follows t h a t w ith increasing world p o pulation an d w ith a lim ited area available for cultivation, it will be necessary in fu tu re to devote m ore a tte n tio n n o t only to increasing food p roduction per acre, b u t also to p rev en tin g those losses w hich are due to weed com petition a n d to th e a c tiv ity of insects and fungi.
The use o f petroleum p ro d u cts in agriculture is n o rm ally associated w ith th e use of fuel an d lu b rican ts in farm m achinery, an d th e ex te n t to which some of these products can assist th e farm er in an en tirely different fashion is often n o t realized. I t is th e purpose of th is p ap er to show how petroleum oil an d petroleum chem icals can serve to increase food supplies, b y pro tectin g p lan ts an d p la n t p ro d u cts from th e n a tu ra l enem ies which so freq u en tly a tta c k them .
The e x te n t to w hich certain insects an d fungi levy a to ll upon m a n ’s food is seldom realized. Few relatively accu rate estim ates hav e ever been m ade and, in fact, th e y are extrem ely difficult to m ake. I t was estim ated ab o u t 1930 th a t in th e U.S.A . alone th e an n u a l loss due to insect pests and fungus diseases am o u n ted to a t least £500 m illion p er an n u m , a n d the loss due to com petition b y weeds is p ro b ab ly g reate r th a n this.
T he concept of a struggle for existence applies to all form s of life. The wild form s of our dom estic p lan ts, such as w h eat a n d p o ta to , survived in th e struggle in spite o f fungal an d insect a tta c k because th e y possessed n a tu ra l, in h eren t resistance to fungi an d were too w idely sc a ttered to be elim inated by th e ir insect enemies. W hen m an selected strain s o f these wild p lan ts which had, from his p o in t o f view, desirable qualities, he freq u en tly reduced n a tu ra l resistance, a n d w hen, a t th e sam e tim e, he m assed sim ilar p lan ts to g eth er in a w h eat or p o ta to field, he produced ideal conditions for th e m u ltiplication of insects a n d fungi, a n d n o t in
freq u en tly in v ited a d ev astatin g a tta c k . W e find, therefore, from very early tim es records of p la n t plagues, some of w hich m ay h av e h a d decisive influence on th e h isto ry of prim itive peoples, leading to th e ir m ass m igration or, possibly, to th e ir elim ination. One m ay recall P h a ra o h ’s plague of locusts, or th e fungal diseases o f corn, “ b lasting an d m ildew ,” which according to th e Mosaic law would afflict th e evildoer.1
T he h isto ry of chemical p la n t p ro tectio n goes back to an cien t times.
H om er, ab o u t 1000 B .C ., m entioned th e “ p est-av ertin g su lp h u r,” and P lin y th e E lder, a.d. 23-70, records th e use of some curious insecticides, one of which was “ th e gall of a green lizard .” W riters in th e M iddle Ages suggest th e use o f lim e-wash, soap, vinegar, tu rp e n tin e , sulphur, pepper, soot, an d tobacco. N evertheless, p la n t p ro tectio n in th e m odern sense is a young science, and cannot y e t claim m ore th a n a few score years of practice.
T he organism s w hich com pete w ith or are p a rasitic u p o n food p lan ts are draw n from th e whole range of th e p la n t an d anim al kingdom . In m an y respects weeds, rep resen tativ e o f th e higher m em bers of th e p lan t kingdom , are th e m ost persisten t an d successful of th e enem ies of m a n ’s crops, having a relatively low sta n d a rd of living, w hich enables th em to grow faste r and m ore profusely th a n th e crop p la n t, so t h a t t]ie la tte r is literally overwhelm ed and choked to d eath . As representatives of th e lower p lan ts,
T H E r6lE O F P E T R O L E U M IN P L A N T P R O T E C T IO N . 205 th e fungi an d b acteria are of first im portance. F ungi are p lan ts which h av e no chlorophyll, an d m u st consequently five upon living p la n ts or anim als (parasitic fungi) or upon decaying organic m a tte r (saprophytic fungi). B acteria are now know n to cause a num ber of p la n t diseases, as well as diseases of m an. I n th e anim al kingdom , since all anim als are either directly or indirectly dependent on p lan ts for fife, th ey m ay all be regarded as being parasitic upon th e p la n t, w ith m an, from th e p la n t’s p o in t of view, the biggest p arasite o f any. The plant-parasites in th e anim al kingdom w ith which we are concerned, however, are m ostly th e insects, th e m ites, an d certain p la n t N em atodes (m inute, thread-like worms frequently present in soil).
I n waging chem ical w arfare against th e enemies of th e p la n t a v ariety of m ethods m ay be used. F ungi m ay be controlled b y preventing th e spores of th e fungus from germ inating w hen th e y alight on th e surface o f th e p la n t, or in some cases th e fungus m ay be killed on th e p lan t. W ith insects it is often possible to kill th e insect in its egg (using an ovicidal spray), or in its larv al stage, as well as in th e ad u lt stage. Occasionally it is possible to use a repellent an d keep th e insect aw ay from th e p la n t to be protected. I n all these cases except th e last nam ed a notable problem arises which is still im perfectly solved. This is th e problem of killing th e living fungus or insect while it is actually on th e living p lant. I t will be appreciated th a t th e susceptibility of th e crop p la n t to in ju ry by some chem icals m ay be greater th a n or as great as th a t of th e spore or insect to be killed. In th is case th e chemical is ruled o u t o f use. The spray chem ist a t all tim es is compelled to m ake his product as fungicidal or insecticidal as possible w ith o u t increasing its p h y totoxicity or power to injure th e crop p lan t.
I t should be pointed o u t here th a t th e crops com m only sprayed are orchard fruits, vegetables, and certain tropical crops such as bananas an d pineapple, since these are valuable, high-priced crops which can carry th e cost o f th e tre a tm e n t. As a general rule cereals are n o t sprayed, b u t atte m p ts are m ade to breed varieties resistan t to fungi, th e chief enemies of grain crops.
Petroleum Oils as In sec ticid es.
The origin of th e use of petroleum oils as insecticides is n o t know n, b u t is probably as old as th e knowledge of petroleum itself. Marco Polo in the th irte e n th cen tu ry described th e use o f crude m ineral oil for treatin g camels against m ange, and it is interesting to note th a t this practice persists to-day in A rabia, except th a t m otor spirit for th e purpose is begged from th e passing m otorist. The relativ ely m odern use of petroleum oils dates from 1865,2 w hen kerosine was recom m ended in th e U.S.A. for use on orange trees for th e control o f scale insects. U ndiluted kerosine is capable of burning th e tre e severely, an d crude em ulsions were soon devised, soap and m ilk being used as emulsifiers to enable th e kerosine to be diluted w ith w ater. E v en w hen diluted, however, th e kerosine emulsions often proved to be p h ytotoxic and, either b y in te n t or b y accident, it was discovered about 1905-1910 th a t lubricating-oil emulsions could be used, th e original oils being th e partially-refined “ red engine oil ” type. Following extensive work by Q uaintance 3 in 1922, th e use of lubricating-oil emulsions, including
206 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
th e m ore highly refined w hite oils, began to spread in th e U .S.A ., an d from ab o u t 1925 in th e U .K . also.
A t th e presen t tim e m an y millions of gallons of sp ra y oils are sold. T he bulk of th e oil is used for application to fru it trees, a n d know ledge of th e p roperties o f h o rtic u ltu ra l spray oils is based largely on experience w ith o rch ard trees, including citru s trees. F o r th is reason, th e m ajo r p a r t of th is pap er will deal w ith orchard sprays, b u t it is w o rth y of n o te t h a t other applications of spray oils in agriculture are developing v ery quickly.
Base Oils of Horticultural Sprays.
T he physical properties o f petroleum oil w hich are of in te re st to the spray m an u factu rer are specific g ra v ity , viscosity, an d vo latility . The only chem ical characteristic used is th e figure for u n su lp h o n ated residue.
A t th e presen t tim e th e so-called w inter oils, used in th e U .K . for applica
tio n to d o rm an t (i.e., leafless) orchard trees to kill certa in insect pests which over-w inter on th e tree in th e egg stage, have a specification as follows :—
Sp. gr.: 0-86 to 0-93 at-T5-5°C/15-5°.
V iscosity : 162 to 172 sec R edw ood I a t 70° F.
V olatility : N o t m ore th a n 5 % distilling a t a n oil te m p e ra tu re of 350° C.
U nsulp h o n ated residue : N o t less th a n 65% by volum e.
On th e o th er h an d , th e so-called sum m er w hite oils, used in tem perate clim ates for application to leaves a n d fru it in th e orch ard or glass-house, an d in th e sem i-tropics for application to c itru s fru it, hav e a specification as under :—
Sp. gr. : 0-84 to 0-92 a t 15-5° C./15-5° (glass-house oils, 0-84 to 0-89).
V olatility : 10% distilling betw een 310° C a n d 340° C 50% distilling betw een 350° C an d 375° C 80% distilling betw een 380° C an d 400° C
U nsulphonated R esidue : N o t less th a n 92% b y volum e (glass-house oils, 95% by volum e).
T he above sta te m e n t gives th e position in its sim plest term s. I n practice th ere is considerable v ariatio n , an d in California, for instance, th e oil used is often selected for th e locality in w hich it will be used, as well as for the tim e of y ear an d th e crop to be sprayed. I t should be s ta te d a t th is stage th a t th e specifications given h av e been arriv ed a t b y a hit-or-m iss process, an d for th e m ost p a rt are based on field observation ra th e r th a n on deliberate biochem ical research. I t is now realized t h a t th e physical characteristics of th e base oil are q uite in ad eq u ate as a guide to its biological activ ity an d th a t fa r m ore should be know n regarding th e ch em istry o f th e oil.
I n th e pre p a ratio n of oil-sprays th e problem is one of m aking a suitable oil concentrate which will dilute freely w ith w ater, w hich u n til recently has been th e universal carrier for th e oil. I n th is em ulsion concentrate w ater is th e continuous phase, since dilution w ith w ater is desired, a n d oil is th e disperse phase, th e emulsifier collecting on th e o il/w ater interface.
I t is, however, possible to use emulsifiers dissolved in th e oil, w ater being absent. The concentrate, w hich is b e st described as a n em ulsible oil, form s an em ulsion on being poured in to w ater. T he problem of m aking oil sprays therefore resolves itself usually in to one of choosing th e a p p ro p riate
T H E R Ô L E O F P E T R O L E U M I N P L A N T P R O T E C T IO N . 207 emulsifiers an d m ethod of ém ulsification, so th a t a concentrate is produced w hich is (a) stable in storage for a long tim e an d over a wide range of tem p eratu res ; (b) capable of producing on dilution w ith n a tu ra l w aters of v arying hardness and p H a working spray fluid which is itself stable enough to rem ain unchanged in th e sp ray ta n k for a num b er of hours and y e t u n stab le enough to “ b re ak ” an d deposit its oil on th e p la n t surface by im pact as well as by drying ; (c) capable, w hen necessary, o f carrying an ad d ed insecticide or fungicide. »
T he principal ty p es of oil-spray concentrate are ta n k m ix, stock emulsion, miscible oil, an d em ulsible oil. The tank-m ix m ethod is one o f th e oldest and, as th e nam e implies, is carried o u t by stirring oil and w ater together in th e spray ta n k w ith suitable q uantities o f emulsifiers such as soap, if th e w ater is soft, and blood album en, certain clays, or B ordeaux precipitate if th e w ater is hard . (B ordeaux M ixture is a widely used fungicide m ade from copper sulphate and h y d ra te d lime.) T ank-m ix emulsions are relatively unstable, require vigorous and sustained agitation, can cause grave dam age to th e tree in unskilled hands, and are n o t used to any ex ten t in th e U .K . Stock emulsions are p aste-type emulsions or m ayonnaises which contain 70 to 80 p er cent of base oil, ab o u t 3 per cent of emulsifiers such as casein, an d ab o u t 20 to 30 per cent of w ater. The oil-w ater-em ulsifier m ixture is passed th ro u g h an em ulsifying mill, care being ta k e n to keep th e finished em ulsion of a consistency suitable for easy m ixing and m easuring in th e field. Stock em ulsions are widely used, especially in h ard w ater areas;
th ey have th e disadvantage th a t th ey ten d to “ cream ” in storage, and to “ b reak ,” liberating free oil, if exposed to frost.
The term s miscible, emulsible, and “ soluble ” are applied to spray concentrates, often som ew hat indiscrim inately, w hen these are one-phase solutions which give emulsions when added to a bulk of w ater. T hey are all solutions o f emulsifiers in oil, th e oil eventually form ing th e disperse phase of th e emulsion. I t would appear desirable to abandon th e use of th e term “ soluble ” in connection w ith spray oils, and th e term “ miscible ” is em ployed here to describe spray oil preparations containing a fairly large percentage of emulsifiers (ca 15 per cent). The emulsibles, on th e other hand, frequently contain 97 to 98 per cent oil, an d 3 per cent or less of emulsifier. Miscible oils have been used for m any years, th e emulsifiers present being, in general, sulphonated fa tty acids, résinâtes, or soaps, w ith a m u tu al solvent such as cresylic acid and a sm all a m ount of w ater. They m ix freely w ith w ater if a 50 : 50 slurry is first m ade before diluting to bulk, a n d are readily m easured an d h an d led . T hey are n o t susceptible to frosting, and are easily seen on th e tree when sprayed, b u t th e y have th e serious disadvantage o f being incom patible w ith h ard w ater and w ith certain insecticide com ponents. E m ulsible oils are of fairly recent origin, an d are gaining in im portance owing to th e very m uch greater range of efficient oil-soluble emulsifiers now available. I t seems likely th a t emulsibles will displace th e oth er types eventually. As exam ples of emulsifiers used here th e p ro p rieta ry products E m ulphor ELA , T rito n X — 100, Mulsor, and V atsol m ay be nam ed, b u t there are m any others.
I n use, th e oil concentrate is diluted w ith w ater so th a t th e spray fluid contains a definite am ount of oil. M any experim ents have shown th a t th e eggs of over-w intering insect pests on deciduous trees an d scale insects on
208 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
citrus are controlled by certain percentages of oil, a n d th e d ilu tio n r a te is ad ju ste d accordingly. I n th is co u n try a w inter-w ash for apples will contain a b o u t 6 per cent oil as sprayed. Oils for citru s fru it a n d for application to foliage {e.g., sum m er orchard sprays, glass-house sprays) are com m only used a t 0-75 to 1-5 p e r cent o f ac tu a l oil in th e read y spray.
Insecticidal Action of Petroleum Oils.
I t is u n fo rtu n ate ly tru e t h a t precise know ledge o f th e m ode of action of oils on insect eggs or ad u lts is lacking. T he problem s o f insect physiology which are raised are exceedingly com plex. T he u su al theories are {a) th a t th e oil acts m echanically by coating th e egg or en terin g th e tra c h e a o f th e a d u lt, th u s p reventing oxygen access or causing carbon dioxide to accum u
late, a n d (b) th a t th e oil acts b y d irect chem ical to x ic ity on th e in sect tissues, possibly interfering in some w ay w ith enzym e action or a c tu a lly dissolving fa ts an d causing th e d isintegration o f lipoid tissue.
The first hypothesis—th e “ stifling ” a ctio n —would indicate th a t relatively high-boiling, high-viscosity oils w ould be th e ty p e required and, in general, it is tru e t h a t th e insecticidal an d ovicidal properties of w inter petroleum oils increase w ith boiling range or w ith viscosity u n til certain m inim a are reached.4- 5 M a rtin6 concluded t h a t th e m inim um effective viscosity u n d er w inter conditions in th e U .K . a n d for oils of m ore th an 60 per cent unsu lp h o n ated residue was 125 sec R edw ood I a t 70° F . The m axim um viscosity should be such th a t ease of handling th e oil u n d er w inter conditions is retain ed and 500 sec R edw ood I a t 70° F is suggested.
I t is clear t h a t “ stifling ” action is n o t th e whole sto ry , since certain insect eggs are unaffected b y refined petroleum oils o f th e ty p e used as base oils for h o rticu ltu ral washes. T hus th ese oils, w hich consist m ainly of sa tu ra te d hydrocarbons, c an n o t kill eggs of apple aphis or apple sucker.
On th e o th er h an d , Tar-oil w in ter washes, w hich are rich in arom atic hydrocarbons, give an effective control o f aphis an d sucker, a n d this is regarded as a chem ical toxic action, being correlated w ith th e co n ten t of arom atic hydrocarbons as assessed b y solubility in dim eth y l sulphate. The w inter-w ashing of fru it trees in th e U .K . resolves itself in to an a tte m p t to kill th e eggs o f five m ajor pests, aphis an d sucker, controlled b y tar-oil an d capsid, w inter m o th an d red spider m ite, controlled b y w inter petroleum an d n o t controlled by tar-oil. In order to avoid th e necessity for using tar-oil a n d petroleum washes separately, th e y are som etim es m ixed, but results are often n o t v ery good, a n d th e norm al, one-spray w inter pro gram m e in th e U .K . com m only em ploys a D N C -petroleum w ash, in which effective control of aphis and sucker is o b tain ed b y adding dinitro-ortho- cresol to th e petroleum oil.
M any a tte m p ts have been m ade to assess th e p a r t p lay ed b y th e u n satu ra te d , sulphonatable com pounds in oil, b u t w ith conflicting results.
B eyond th e general conclusion th a t dam age to th e p la n t is largely due to th e u n sa tu ra te s an d th a t oils for application to foliage should n o t contain m ore th a n 4 to 10 per cent sulphonatable com pounds, little definite know ledge has emerged. H ow ever, recent w ork b y C hapm an an d Pearce 7 indicates th a t th e origin of th e base oil is very im p o rta n t. T here is evidence th a t paraffinic oils are m ore insecticidal an d less p h ytocidal th a n nap h th en ic
T H E H O L E O E P E T R O L E U M I N P L A N T P R O T E C T IO N . 209 ty p es, an d t h a t th e figure for unsulphonated residue m u st he in terp reted in th e fight of one’s knowledge of th e oil ty p e. I f th is conclusion is generally confirmed it will lead to changes in th e cu rren t specifications for agricultural base oils an d a move in th e direction of allowing th e chem ist an d th e biochem ist, ra th e r th a n th e petroleum physicist, to d ictate th e specification.
Phytocidal Action of Petroleum Oils.
I t has been pointed o u t earlier t h a t th e spray chem ist has to solve th e problem of killing organism s in co n tact w ith th e p la n t w ith o u t dam aging th e p la n t itself. Obviously th e problem is easier to solve, in th e case of deciduous fru it, w hen th e tre e is d o rm an t in w inter th a n when it is carrying sensitive an d delicate young foliage, fru it, an d shoots. F o r th is reason petroleum oils are applied to deciduous fru it chiefly in th e d orm ant season, or in th e “ delayed d o rm an t ” period preceding b u d-burst. I n th e case of th e evergreen citrus tree, oil is applied to foliage an d fruit, and experience has shown t h a t th e tree is fairly resistan t to dam age. H ighly refined w hite oil is also applied to deciduous fru it in full leaf, b u t there is th e n danger of injury. I n all cases trees w eakened b y m alnutrition, drought, or fro st are more susceptible to oil in ju ry th a n h ealthy, vigorous trees.
Oil in ju ry m ay be acute, as shown b y extensive leaf an d fru it drop, or chronic, as shown by bud-kill, delayed b ud developm ent, yellowing of leaves, and, in bad cases, d eath of th e wood. A cute in ju ry is often exhibited w ithin a few days of spraying, b u t chronic in ju ry m ay ta k e weeks to develop. I n th e case o f oranges, an d to a lesser e x te n t grape-fruit, oil in ju ry shows itself as w atery patches (“ w ater-spot ” ) on th e fru it, especially w ith navel oranges, and loss of sugars a n d to ta l solids.
I t is now clear th a t oil p en etrates into th e p la n t tissue and causes d istu rb ances in respiration, tran sp iratio n , an d carbon assim ilation; it m ay 'also affect th e norm al production o f plant-grow th regulators or “ horm ones ” in leaf and fru it. The th e o ry th a t oil-shock leading to fruit-drop is associated w ith interference w ith th e production of th e “ horm one ” which prevents th e form ation of th e m a tu re abscission layer in th e stalk has received some support recently b y field w ork in which fruit-drop has been prevented by incorporating a sy n th etic grow th regulating substance in a sum m er w hite oilspray. 8
The p en e tratio n of oil in to plant-tissue has been stu d ied b y de Ong, K night, and C ham berlin,9 who found th a t oils o f low viscosity are safer to use on citrus th a n those o f high viscosity. The form er oils disappeared from foliage m ore rap id ly th a n th e la tte r, although th is is probably due to absorption ra th e r th a n to volatilization. I t is evident th a t th e q u a n tity of oil retained on th e leaf surface is im p o rtan t, as well as th e q u ality o f th e oil.
The oil deposit is affected n o t only b y th e oil concentration in th e spray applied, b u t also b y th e “ breaking ” qualities of th e emulsion. I t has been argued, therefore, th a t for foliage sprays emulsions of th e greatest sta b ility consistent w ith insecticidal efficiency should be used.10 I t is also a well-known rule in p ractical spraying th a t trees should never be “ double
sprayed ” (i.e., sprayed again soon after drying), although th is is som etim es difficult to avoid w hen th e spray drifts in a strong wind.
A ttem p ts are now being m ade to isolate and identify th e com ponents in an
21 0 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
oil w hich are chiefly responsible for th e dam age. I n th is w ork, as in th e case o f th e in q u iry in to th e insecticidal n a tu re of oil, th e problem s facing th e oil chem ist a n d th e physiologist are com plex. F ro m th e grow er’s p o in t of view it is n o t sufficient for th e sp ray m an u fac tu rer to supply an oil which is generally b u t n o t in v ariab ly safe in use. I n consequence, an oil m u st be provided w hich has a wide m argin of safety, so t h a t it can be used by sp ray team s o f indifferent skill, on trees insufficiently supplied w ith n u trie n ts a n d w ater, u n d e r widely vary in g clim atic conditions, an d still w ith o u t dam age to th e p la n t. I t is n o t surprising t h a t perfect sp ray oils have y e t to be evolved.
Petroleum Oil as a Ca r r ie r.
I n ad d itio n to its own in h e ren t properties as a n insecticide, eith er for killing insect eggs on th e d o rm a n t tre e or a d u lt scale insects or m ites on leaves an d fru it, oil has o u tstan d in g properties as a carrier for o th er insecti
cides an d fungicides. I t has been p ointed o u t earlier t h a t a pro tectiv e cover to leaves an d fru it m ay be necessary, eith er to p re v e n t th e germ ination of fungal spores which alight on th e p la n t tissue or to kill leaf-eating insects by a stom ach poison effect. To ta k e exam ples, th e m o st im p o rta n t fungus a tta c k in g tom atoes in th e glass-house is leaf-m ould, Cladosporium fulvum, which delights in th e w arm , hum id atm osphere provided u n d er glass and can wipe o u t th e en tire crop if unchecked. A highly refined w hite oil, incorporating a fungicide w hich is a specific for leaf-m ould, will give com
plete control of th e fungus, th e oil n o t only killing a n o th e r com m on glass
house p est, red spider m ite, b u t also w ettin g th e w ater-repellent leaf and 'enabling th e fungicide to adhere closely a n d tenaciously to th e leaf and fru it surface. Sim ilarly, a sum m er w hite oil can be used w ith excellent results as a carrier for th e co n tact poison nicotine for th e control of woolly aphis (Eriosoma lanigerum), w hich form s th e w hite, w axy filam ents so com m on in sum m er on neglected garden fru it trees. H ere p e n e tratio n of th e nicotine to th e aphides p ro tected b y th e ir w axy covering w ould be im possible w ith o u t th e use of oil or o th er w ettin g agent.
The im portance of oil as a carrier an d w e tte r has been enhanced b y the in tro d u ctio n of D .D .T. I t is com m on know ledge t h a t th is new insecticide possesses astonishing residual properties as a co n tact poison. T he use of a w ettab le D JD.T. pow der w ith a petroleum sp ray is likely to becom e stan d ard practice for th e control of tw o im p o rta n t orch ard pests, capsid bug (Plesiocoris rugicollis Fall.) and apple blossom weevil (Anthonomuspomorum LI Curt.), for here th e residual value of th e D .D .T . is given full effect by the
“ sticking ” effect of th e oil.
F inally, it seems possible t h a t oil as a com bined insecticide an d carrier m ay be even m ore im p o rta n t in fu tu re if ato m iz atio n procedure becomes sta n d a rd practice. I n th is new developm ent w a ter an d em ulsifiers are discarded, a n d stra ig h t oil, w ith or w ith o u t ad d ed fungicides an d /o r insecticides, is “ atom ized ” in a fast-travelling air-stream a n d carried to all p a rts o f th e tree or p la n t. This process can be a d a p te d b o th to th e orchard an d to th e field crop, an d offers g re at ad v an tag es in speed and cost over th e conventional m ethods. I t can also be m odified for use in aerial spraying.
T H E R Ô L E O F P E T R O L E U M I N P L A N T P R O T E C T IO N . 211
Th e Protection of Stored Pro d u ce.
The fight against th e insect pests of food and o th er agricultural p roducts does n o t cease w hen th e crop is harvested. I t is com m only necessary to store cereal graiiis, peas, beans, an d such diverse products as dried fru it, oil seeds, tobacco, cotton, copra, cocoa, an d others for considerable periods.
Storage m ay be necessary in an A siatic “ go-down ” while aw aiting ship
m ent, or in a C anadian grain silo, or in a L ondon dock warehouse. I t frequently happens th a t crops are insect-infested w hen th e y come in from th e field or p lan tatio n , or th e storage place itse lf m ay h arb o u r m any pests. I n these cases losses in storage m ay be v ery considerable, and m ore th a n h a lf th e crop m ay be rendered unfit for use.
I n th e p a st th e m ost effective w ay o f dealing w ith th e insect pests of stored produce was to fum igate th e m aterial an d th e warehouse w ith a poisonous gas, such as hydrogen cyanide, m ethyl brom ide, or ethylene oxide.
F um igation is a skilled job, an d is n o t w ith o u t danger, owing to th e to x icity to m en of th e gases em ployed. D uring recent years a tte m p ts have been, m ade to develop safer gases, an d one such pro d u ct on th e m ark et is m eth- allyl chloride, a highly effective gaseous fum igant derived from isobutylene, itself isolated from cracking gases.
I t is now possible also to tr e a t warehouses a n d silos w ith a w hite oil containing p y reth ru m or an oil em ulsion containing D .D .T. so th a t a residue toxic to insects is left on th e surfaces tre a te d . I n th is w ay insects hiding in cracks an d crevices can be killed w hen th e y emerge, an d th e tre a tm e n t of storage places too freely v en tilated to be fum igated becomes possible.
Petroleum Oils as We ed Kil l e r s.
W eed-killers m ay be divided into tw o m ain classes : those which kill all plants, an d those selective weed-killers which kill one p la n t while leaving another unharm ed. N on-selective herbicides are widely used on roads, rail-tracks, and drainage and irrigation ditches. D uring th e p a st te n years diesel oil has been used on a large scale in citrus groves in California as a non-selective weed-killer. The oil is sprayed over th e ground surface a t th e ra te of ab o u t 10 0 gallons per acre, an d expensive cultivation and harm ful root disturbance are elim inated. A fter several applications all weeds are destroyed, an d a clean surface is left w hich prom otes w ater retention and perm its easy spraying an d harvesting operations. I t should be noted th a t this procedure is ad ap te d to flat, irrigated lands. I n o th er areas it m ight be undesirable to kill all weeds, since serious soil erosion m ight follow, and here again occasional oiling checks weed grow th, while p erm itting roots to survive a n d regeneration to occur.
The problem of developing a selective weed-killer is sim ilar to th e problem of m aking an ideal sp ray oil, for in th is case also th e object is to kill one living organism while leaving another adjacent organism u n h u rt. This is by fa r th e m ost im p o rta n t use of weedicides, an d very g reat advances are likely to be m ade in th is sphere as intensive cultivation spreads an d labour becomes m ore expensive. The m ost recent contribution to th is problem is th e in tro d u ctio n of a new range of herbicides—th e “ horm one ” ty p e —- which are extrao rd in arily effective in certain cases. Thus yellow charlock—
212 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
one of th e w orst weeds o f E nglish cornlands— can now be elim inated quickly an d cheaply by spraying or dusting w ith 1 lb of 2 -4 D (2-, 4-dichlorphenoxy- acetic acid) per acre. This m aterial m ay also be applied w ith th e fertilizer, so th a t th e corn is encouraged to grow an d th e weed suppressed in one and th e sam e operation. Some horm one sprays are ex trem ely specialized, an d although w ith o u t effect on grasses a n d cereals a t th e d ilu tio n used, th e y are deadly n o t only to m an y weeds, b u t also to th e m a jo rity o f b ro ad leaved farm crops. Oil is less d rastic in its effect, a n d recen tly v ery success
ful use o f kerosine has been re p o rted 11 for th e tre a tm e n t of c arro t and p arsn ip crops. W hen grown on th e large scale these crops absorb m uch h an d lab o u r for weeding, w hich c an n o t be carried o u t m echanically.
Kerosines of certain types, sp ray ed along th e row s a t th e ra te o f 80 to 100 gallons p er acre, can kill m o st com m on weeds w ith o u t affecting th e young carrots or parsnips, an d c u t th e cost of weeding to a fractio n of its norm al figure.
Petroleum Chem icals in Ag r ic u l t u r e.
T he chemical in d u stry based upon petroleum w hich has been developing in m ushroom fashion during th e la s t te n years has a lread y produced chem icals o f g re a t in tere st to th e farm er. T hus hydrogen o b tain ed from n a tu ra l or refinery gases is now being converted in to am m onia, using atm ospheric nitrogen, on a large scale. This am m onia is used as a fertilizer in th e form of am m onium su lp h ate or, b y a proem s developed b y th e Shell Chemical Co. in California, it m ay be used in th e form o f liquid, anhydrous am m onia for injection in to irrigation w ater or in to th e soil.
D uring recent years an o th er petroleum chem ical w hich has proved to be o f service to th e farm er, as well as being of g reat in d u stria l im portance, is th e m ix tu re of sodium secondary alkyl sulp h ates know n as “ ester salts.”
T his m ix tu re of long-chain alkyl sulp h ates is m ade b y th e reaction of petroleum olefins w ith sulphuric acid. T he acid/olefin reactio n m ixture is neutralized w ith caustic soda, a n d th e “ ester salts ” produced, w hich are highly surface-active, a n d fully efficient even in h a rd w ater, are used in agriculture as w etters an d spreaders for carrying insecticides a n d fungicides in to close c o n tact w ith insects or foliage. T hey m a y also be used w ith weed-killers an d w ith th e p la n t “ horm one ” sprays used for th e prevention o f pre-harvest drop of apples an d pears. Éüxed w ith alkalis, th e y form efficient d etergents for rem oving m ilk residues from d a iry equipm ent.
One of th e m ost notable of th e new additions to th e fa rm e r’s arm o u ry of chem ical w eapons is a soil fu m ig an t consisting largely o f a m ix tu re of dichloropropene an d dichloropropane (D -D M ixture). H ith e rto it has been impossible for th e farm er to control certain w idespread soil pests, and in p a rtic u la r nem atodes or eelworms, because alth o u g h chem ical tre atm en ts are know n, th e y are insufficiently effective a n d im possibly expensive. In th e glass-house th e pests are com m only controlled by steam ing th e soil, a t a cost which m ay reach £300 p er acre. I n th e field th e only rem edy, h ith erto , has been to avoid growing susceptible crops for a long period of y ears—a process which m ay cause considerable m o n etary loss.
D -D is a d a rk brow n liquid consisting o f a m ix tu re o f chlorinated C3 hydrocarbons, of w hich 1: 3-dichloropropene is th e m ost im p o rta n t, p ro duced by th e controlled^chlorination of propylene an d o th er gases o b tain ed
from certain petroleum fractions. I t is injected in to th e soil b y special m achines, which place th e liquid a t a d ep th of 6 to 8 inches a t th e ra te of 200 to 600 lb per acre. The liquid vaporizes, and th e fum igation causes th e suppression of a num ber of harm ful soil organisms, including nem atodes, wire-worm, an d certain fungi, and stim ulates th e crop, which is sown or p lan ted afte r fum igation, to m ore vigorous grow th, giving g reatly increased yield. A large v a riety of crops is now being tre a te d w ith D -D , and extrem ely good results have been recorded w ith pineapple in H aw aii and w ith m an y m arket-garden crops in th e U.S.A. In th e U .K . large areas o f some of th e m ost fertile p o ta to and sugar-beet lands are infested w ith nem atodes, an d w ork on th e developm ent of D -D for use on th e farm an d in th e glass-house b o th here and on th e C ontinent is actively in progress.
Tim e does n o t perm it an account of th e way in which petroleum products are being used to com bat th e th ree m ajor insect pests—locust, m osquito, an d tsetse—which directly or indirectly affect food production, often to a serious e x ten t. I t is clear th a t petroleum is a treasure-house from which th e chem ist can e x tra c t a v a st diversity of m aterials, and from which m an can hope to o b tain in th e fu tu re increasing assistance in his unending b a ttle for his daily bread.
References.
1 D eu tero n o m y X X V I I I . 22.
2 L o d em an , E . G. “ T h e S p ra y in g o f P la n ts .” New Y ork, 1903, p. 79.
3 Q u ain tan o e, A. L . 1922, U .S . Dept. A gric. C lip 'S h ee t 193.
4 A u stin , M. D ., J a r y , S. G., a n d M a rtin , H . J . S .-E . A gric. Coll., W ye, 1932, 30, 63; 1 9 3 3 ,3 2 ,6 3 ; 1 9 3 4 ,3 4 ,1 1 4 ; 1 9 3 5 ,3 6 ,8 6 .
6 Spuler, A ., O v erley , F . L ., a n d G reen, E . L . 1931, W ashington A gric. E x p . S ta tio n ,
B u ll. 252. i
6 M artin , H . A n n . A p p l. B io l., 1935, 22, 334.
7 C h ap m an , P . J . , P e a rce , G. W ., a n d A vens, A. W . J . Econ. E n t., 36, (2), 241.
8 Cole, L . W . L ., a n d H eeley, W . U np u b lish ed .
9 de O ng, E . R ., K n ig h t, H ., a n d C ham berlin, J . C. H ilgardia, 1927, 2, 351.
10 M a rtin , H . “ T h e Scientific P rin cip les o f P la n t P ro te c tio n ,” 3rd ed ., 1940, p. 206.
11 H a rd y , W . D . A gric. Oaz. N ew S o uth Wales, N ov. 1944, L V , p a r t 2.
Discussion.
Mr. C. L. Gilb e r t : The lecturer is to be congratulated on having tak en us on so interesting and instructive an excursion along one of th e more unfam iliar by-paths in th e field of petroleum . The subject is com paratively new to m ost of th e m em bers of th e In s titu te o f Petroleum , b u t, nevertheless, it is one of very great im portance, o u t of all proportion to th e small quantities of petroleum used as com pared w ith th e quantities em ployed for other p u r
poses. The paper is also of interest as showing how wide are th e ram ifications of th e petroleum in d u stry of th e present day, and th e ex te n t to which it is necessary for th e petroleum technologists to keep in touch w ith so m any other sciences. Indeed, in these days there are very few sciences which are no t closely linked w ith th e petroleum industry, an d th u s it is necessary for th e technologist to be a m an of m any p arts. The entomological and biological fields are some distance rem oved from petroleum technology, so th a t it is all th e more gratifying to find w hat a m ajor p a rt th e petroleum in d u stry is playing in m odern developm ents in this field.
W hen we tr y to determ ine how petroleum products play their p a rt in
T H E H O L E O F P E T R O L E U M I N P L A N T P R O T E C T IO N .—D IS C U S S IO N . 213
214 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
practice we are up against th e difficulty th a t we do n o t know how th e com position of oils is related to th e ir behaviour. This suggests th a t present- d a y m ethods of classifying th e com ponents of hydrocarbons is quite insufficient. T he p resen t classification, in term s of arom atics, paraffins and n ap h th en e hydrocarbons, does n o t ta k e us far enough. T hus th e arom atic class of hydrocarbons ocpurs in widely different raw m aterials, a n d some m em bers of th is class m ay differ from others in th e ir effect on th e grow ths of p la n t cells, as th e y do in th e case of anim al cell grow th. Also, in th e case of tu rb in e oils an d tran sfo rm er oils, certain m em bers o f a p articu lar class of hydrocarbons are technically m ore significant th a n others in th a t class.
T he m ethods described for th e p ro tectio n of p la n ts cover various aspects, including th e control of grow th of th e p la n t itself. T h a t is a v ery radical d ep artu re, an d fu rth e r research along these lines will p ro b ab ly th ro w a great deal of fight on th e life process itself. This technique, therefore, will require very careful control. I t seems t h a t if th e m ethods described are fully applied, th e resulting increase o f crops will be sufficient to provide th e world w ith a really ad eq u ate food supply : an d it is gratifying t h a t th e petroleum in d u stry is tak in g a n activ e p a r t in th is work.
I should like to ask a question w hich relates to th e m eth o d m entioned for applying oil in a cu rren t of air, ra th e r th a n in th e form of a sp ray through a nozzle. There is ra th e r a tre n d in these days to use d u sts in th e form of very fine particles, or insecticides in th e form of aerosols, an d it is con
sidered th a t th e finer th e particle size, th e m ore effective is th e insecticide.
I w ould ask w hether, in th e case of oil applied b y m eans o f an a ir spray, the in ten tio n is to produce sm all drops which are m ore effective, -or which do less dam age to th e plants.
Mr. Leyland Cole : T he process of atom izing oil a n d using air instead of w ate r as th e carrier is com paratively new. I n reg ard to particle size one requires, o f course, in th e case of a n ovicidal spray, a certain m inim um covering o f th e egg if it is to be stifled, an d perhaps t h a t can be achieved only by using a fair volum e of particles of a size considerably above those found in aerosols. Again, in th e case of a p ro tectiv e fungicide, a layer of a d eq u ate con tin u ity and thickness is required on th e leaf an d fru it an d one m u st a d ju st th e particle size to give an ad eq u ate layer.
H owever, th e technique is new, an d we have n o t progressed fa r enough to be able to give an answ er to y our query.
Mr. E . G. Ellis : I should like to express m y th a n k s to th e a u th o r for his very interesting paper, which I have found so stim u latin g t h a t I am p ro m p ted to ask a num ber of questions.
The a u th o r’s m ention of sulphur com pounds rem inds m e of a n occasion in m y early y o u th , w hen we prepared a p ro d u ct for th e ex term in atio n of th e R ed Spider. W e m ade a m ost revolting m ix tu re of sulphur and, I believe, potassium o le a te ; b u t it was effective.
My n e x t incursion in to th is field was to ap p ly a hom e-m ade em ulsion of m ineral oil to ram bler roses infested b y green aphis. I th in k th e aphis was slightly resentful, a n d did n o t ta k e very m uch no tice ; b u t th e emulsion would have won first prize for p h y to to x ic ity !
A n aspect o f th e subject on which I should have liked a little more info rm atio n is th a t o f th e preservation of produce. L ately we have been hearing quite a lot ab o u t th e m ethod of preserving fru it an d vegetables by coating either w ith w ax, or w ith m ineral oil alone or w ith a m ineral oil emulsion. I n th is country, so fa r as I know, th e w ork has been confined m ainly to apples, a n d th e m ethod takes th e place to a certain ex ten t of controlled gas storage. I n other words, th e in tern al atm osphere is so balanced by th e diffusion ra te of oxygen and carbon dioxide through th e layer of w ax or oil, th a t th e fru it m ay be preserved under ordinary barn storage conditions for a considerably longer period th a n norm ally.
W ork has been done by th e D e p artm en t of Scientific an d In d u strial Research, a n d it once m ore introduced th e dual difficulty th a t, whereas you m ay have an emulsion which gives apparently, from th e physical side, anyhow , a continuous coating, th e in tern al atm osphere is disturbed.
F o r exam ple, th c o x y g e n content will be too low, an d although th e fru it does n o t necessarily ro t, it m ay over a period develop w hat is, to m any people, an u npleasant alcoholic taste. I do n o t find it so unpleasant ! A t th e sam e tim e, I understan d th a t th e effect on th e actu al skin of th e apple gives rise to difficulty, m ore p articu larly w ith th e well-known ty p e of Cox’s Orange Pippin, which is p articu larly susceptible to it, whereas th e fru it of th e more ro b u st types, such as th e B ram ley and th e G ranny Sm ith, has a n a tu ra l w ax occurring in th e skin to a larger ex ten t and is m uch less susceptible. I t has also been found th a t even th e highly refined, acid washed, w hite oils can them selves be harm ful. F a r less harm ful are vegetable oils of th e p e a n u t ty p e ; an d I believe th a t a m ixture of th e two has been used.
The coarser fru it from our own colonies or from America is very m uch less susceptible, an d I understand th a t it can be k e p t in an eatable condition by straightforw ard spray, atom ised perhaps, of either th e w hite oils or wax emulsions.
However, perhaps now or later th e a u th o r m ay be able to allude fu rth er to this very fruitful ground for research.
Mr. Leyland Cole : I do n o t th in k th a t I can add a g reat deal to w hat Mr. Ellis has told us. I t is certainly tru e th a t arachis oil (peanut oil) has proved more effective th a n even refined w hite oils. This work is still p ro ceeding in th e laboratories. The g reat trouble h ith erto has been a spotting of th e skin of th e fru it, leading to in tern al cell breakdow n, for which no one as y et seems to be able to find a rem edy.
Mr. E. Thornton : Sometimes it has been found th a t particu lar insects can in th e course o f tim e a d ju st them selves to some insecticides of a chemical character, an d th erea fter continue to breed. Is there an y evidence th a t oil sprays m ay become less effective in th e course of tim e due to the intended victim s adjusting them selves to w ith stan d th e a tta c k ?
Mr. Leyland Cole : The answer a t th e present tim e is “ N o.” W h at you have described is tru e of hydrogen cyanide, p articularly w hen used for fum igating citrus trees, an d th a t is perhaps one of th e reasons w hy oil spraying has succeeded in usurping th e position form erly held in some areas
T H E R Ô L E O P P E T R O L E U M IN P L A N T P R O T E C T IO N .— D IS C U S S IO N . 215
216 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E :
b y HCN. I t is tru e also t h a t some insects, p articu larly those a tta c k in g anim als, eventually become im m une from th e effects o f arsenic, w hich is com m only used to control them . B u t in all these cases arsenic has been used for a long tim e, a n d presum ably resista n t races of insects hav e been developed. W h eth er it is possible t h a t oil has n o t y e t been used for a sufficient length of tim e for t h a t to occur, I do n o t know , b u t I ra th e r th in k th e sam e effect will n o t be shown. O f course, oil is used largely as an ovicide, or as a • carrier for o th e r insecticides a n d fungicides, w ith th e n otable exception t h a t oil alone will control th e m ites, p articu larly th e R ed Spider m ite, b o th th e a d u lt an d th e egg, a n d also th e a d u lt form of m any Scale insects.
Th e Chairman : Mr. L eyland Cole has given us, as I expected, an extrem ely able survey of th is field and, as he im plied a t th e beginning, it has needed tw o dreadful w ars to bring th is m odern civilization of ours to realize w h at a very narrow m argin th ere is betw een production an d con
sum ption, betw een a production sufficient to m eet th e w orld’s requirem ents, on th e one h and, an d real danger of sta rv a tio n on th e oth er h an d . B u t I th in k we are becoming alert to th e situ atio n now, so m uch so th a t agri
cu ltu ral specialists are realizing it is n o t m erely a question of th e q u an tity , availability an d balance o f food n u trie n ts in th e soil to w hich we have to look, b u t th ere is som ething, entirely different a n d p ro b ab ly o f even g reater im portance in reference to food production, a n d th a t is th e balance betw een th e p la n t a n d its enemies. W ith th e realizatio n o f w h a t is required, chem ical w arfare against such enemies is m ore a n d m ore receiving th e a tte n tio n it deserves.
I t is significant th a t such a tte n tio n is being paid, n o t only a t th e uni
versities an d agricultural colleges, b u t now in th e laboratories a n d experi
m ental statio n s of our own g rea t oil in d u s tr y ; a n d I do n o t th in k we need to consider we are praising ourselves u n d u ly in saying th a t th e e n try of the petroleum in d u stry in to th is field is bound to have a v ery big effect. W e are so well furnished in personnel, in knowledge, in technique a n d in equip
m en t th a t, if th e investigations w hich are obviously u n d er w ay progress in th e sam e spirit a n d to th e sam e e x te n t as o th er investigations we have m ade, we are bound to get results w hich will be reflected in th e increased production o f food to which th e world looks forw ard.
I would have liked to h av e been able to discuss th e whole of this fine paper, b u t tim e does n o t perm it. B u t I should like to m ake special reference to th e question of soil tre a tm e n t, w ith w hich I am directly per
sonally concerned. E v e r since E . J . R ussell’s w ork on th e so-called partial sterilization of soil it has been quite a p p a re n t th a t th e far-reaching effects which were observable would have still w ider fields to conquer an d th a t a m uch m ore selective application of th a t m eth o d was likely to come. As Mr. L eyland Cole has pointed out, it is n o t alw ays possible in th e ordinary w ay to go in for w h at is, after all, th e ra th e r crude m ethod of soil steam ing to effect th is p a rtia l sterilizatio n ; it is v ery expensive a n d v ery cum ber
some, an d even under glass has been largely given up. B u t th e effect of chemicals is quite m arked, a n d in some of m y own houses th e sam e soil has been in use for m ore th a n tw enty-five years, w ith an an n u al tre a tm e n t by chemicals. This is chiefly for tom atoes, which is a crop p articu larly
T H E R Ô L E O F P E T R O L E U M IN P L A N T P R O T E C T IO N .— D IS C U S S IO N . 217 susceptible to soil conditions. Such continuous cropping has n o t by any m eans reduced th e yield; indeed, yields are higher now th a n a t th e beginning.
I am very m uch im pressed an d encouraged therefore by th e a u th o r’s reference to D-D, em anating so directly from petroleum , an d which gives th e possibility of th is chemical tre a tm e n t o f soil being ta k e n beyond th e glass-house to th e m ark et garden or even to field agriculture. I f he could give us even a broad or a rough idea of w h at th e costs of using D-D are likely to be, as com pared w ith, say, form aldehyde, which has proved very useful against soil fungi, it would be o f interest.
The second m a tte r I should like to emphasize is th a t o f weed control.
In the case of th e carrot crop, for exam ple, we have to consider th e specific n ature o f th e selective weed controller. This question of selective control is in its infancy, b u t close investigation of th e various types of grow th is quite likely to lead to m ost effective results. The real an d obvious danger, though it is one which can be tak e n care of, is th e upsetting of n a tu ra l balances, especially in th e early stages of grow th. B ut, in view of th e encouraging results obtained so far, I th in k we can look forw ard to con
siderable success in selective weed destruction. I can confirm, from m y own observations in th e U nited S tates, th e effects of some of th e chosen petroleum distillates—m ostly by-products of catalytic cracking— on carrot crops and parsnips, which are very difficult to handle and for which hoeing is alm ost beyond consideration. I f th e soil is loosened by hoeing, there is th e chance, n o t only of uprooting th e carrots, b u t of lettin g in fly. I f the weed is killed in th e early stages, it m akes all th e difference to th e subsequent cropping.
Non-selective weed-killing is m uch sim pler, an d here again m arked advances have been m ade in large-scale weed destruction b y th e use of petroleum distillates, especially where it is wished to get rid of everything th a t is growing, an d ju s t leave th e lan d bare. We sta rte d w ork on th is originally because of availability of arom atic products from catalytic cracking. D istillates of boiling range 350° to 650°, an d w ith an arom atic content of betw een 60 a n d 80 per cent, are especially effective. Those w ith less th a n 50 p er cent, of arom atics ta il off m arkedly in respect of a c tiv ity ; bu t where this figure is exceeded th e cracked petroleum products will destroy annuals w ith one spraying and, in th e case of perennials, tw o or a t m ost three sprayings are sufficient to clear th em aw ay. B y th is m eans it has been possible to clear aw ay th e g reatest weed grow ths in an d around refineries, along railw ay em bankm ents, an d so on. I t is im p o rta n t to be able to control such grow ths because of fire hazards. In th e p a s t it has only been possible to do it w ith arsenates, chlorates, an d so on, which are objectionable to anim als. The petroleum products are sufficiently volatile so th a t th ey will disappear in th e course o f tim e.
I look forw ard w ith confidence to fu tu re developm ents an d to th e incursion of th e petroleum chem ist into this great field of p la n t protection and th e encouraging o f cropping by such means.
Mr. Leyland Cole : I th in k it will be appreciated th a t I have d ealt w ith some of these uses of petroleum chemicals in a som ew hat sketchy fa sh io n ; th e danger is th a t m y enthusiasm m ight ru n aw ay w ith me and
I m ig h t ta lk for fa r too long. T h a t is p articu larly tru e of th e m ate ria l D-D , which has g reat potentialities, a n d it is also tru e of w eed-killers.
The C hairm an has asked ab o u t th e cost o f applying D-D , as com pared w ith applying form aldehyde. As y ou know , form aldehyde is p rim arily a fungicide a n d is n o t capable of killing eelworm, w hereas th e use of D -D is directed prim arily ag ain st t h a t pest, as well as ag ain st wirew orm s an d other h arm ful insects. T he to ta l cost in th e glass-houses will w ork o u t, I th in k , a t betw een £20 an d £30 per acre, w hich is considerably higher th a n th e cost of form aldehyde, b u t only a frac tio n of th e cost o f steam ing, an d the sam e so rt of figure will ap p ly in th e field. T he labour cost of h a n d applica
tio n is high. W e are developing m achines for applying D-D in th e field an d in th e nursery a n d we shall reduce th e cost of ap plication in th is way.
W e do n o t y e t know for how long, u n d er E nglish conditions, th e effect o f th e fum igant will persist. W e have good reason to believe t h a t it will la st for m ore th a n a year, possibly for th re e years or even longer. There
fore, th e to ta l cost m u st be divided by th e num b er o f years over which the effect will persist, in order to arrive a t th e an n u a l cost. T here is a n article in The Scottish Journal of Agriculture for J a n u a ry , 1947, on independent w ork w ith D -D in Scotland, showing t h a t th e application of 300 lb of D-D per acre resulted in th e three-fold m u ltiplication o f a to m a to c r o p ; th e cost o f th e application was outw eighed m an y tim es b y th e value o f th e ex tra crop produced.
W ith regard to weed-killers, th ere are m an y refineries w here expenditure on th e d estruction of weeds on th e refinery area is high, since h a n d labour is used. I t is quite clear th a t some of th e m aterials o b tain ab le a t the refinery would to a large e x te n t ren d er th a t h a n d lab o u r unnecessary.
I t seems t h a t we have a g re at deal m ore to learn a b o u t petroleum pro
ducts from th e p o in t of view of th e ir use as selective weed-killers, a use which is extrem ely im p o rta n t an d w hich p resents difficult problem s. T he killing of one g ro w th , w hilst leaving an o th er unharm ed, is a problem involving the m aintenance of a certain m argin of safety all th e tim e, because w h at you can do in experim ental w ork m ay n o t necessarily be done b y th e worker in th e field. Y ou m ay stip u la te th e ap plication of 50 gallons per acre, but th e w orker in th e field m ay give a little e x tra dose “ for lu ck ,” an d so destroy th e whole crop. C ertainly we do n o t know enough ab o u t th e subject y et.
I n th e case of th e non-selective weed-killer, of course, th e problem is very m uch easier. W here one has to clear whole areas, p a rtic u la rly those which are n o t subject to soil erosion, reasonably cheap oil, if available, does form an adm irable su b stitu te for th e ra th e r dangerous arsenicals or chlorates w hich are so widely used.
On th e m otion of th e C hairm an, a h e a rty vo te of th a n k s was accorded Mr. L eyland Cole for his paper.
218 C O L E : P E T R O L E U M P R O D U C T S I N A G R IC U L T U R E .— D IS C U S S I O N .
THE APPLICATION OF THE PRINCIPLES OF CLAY CHEMISTRY TO PROBLEMS ENCOUNTERED W HEN DRILLING IN TRINIDAD CLAYS.*
B y H . C. H . Da rley, B.Sc. (Associate Me m b e r).
Sy n o p s i s.
S u ch p ro p e rtie s o f clay s a s affect d rillin g p ro b lem s a re discussed. I t is show n t h a t w ith clay -b ase m u d s, in o rd e r to m a in ta in th e c h a ra c te ris tic s n ecessary fo r d rillin g a high degree o f d ispersion o f th e c la y p a rtic le s is req u ire d , b u t t h a t th e disp ersio n a g e n ts re a c t on th e b it c u ttin g s a n d fo rm a tio n to cause ra p id rises in v isco sity , “ stic k y ” d rillin g -with co n seq u en t low ra te s o f p e n e tra tio n , a n d to p ro m o te caving. A tte m p ts to m itig a te th ese difficulties w ith clay -b ase m u d s a re d escribed. A lte rn a tiv e s to clay-base m u d s a re discussed a n d th e re s u lts o f la b o ra to ry te s ts o f s ta rc h m u d s c o n ta in in g flo ccu latin g a g e n ts a re given. A n a cc o u n t is given o f th e tr ia l o f a sta rc h —
a l u m i n i u m su lp h a te drillin g fluid, w hich gave a m a rk e d increase in th e r a te of p e n e tra tio n b u t d e v elo p ed excessive gel stre n g th s . T he p ro p e rtie s o f a sta rc h -so d iu m -c h lo rid e -s o d iu m silicate d rillin g fluid, w hich a p p ea red to offer a so lu tio n to th e p ro b lem s u n d e r discussion, a re given.
Introduction.
Down to th e to p of th e Lower Cruse horizon th e form ations in T rinidad are m ostly sands an d sandy clay an d generally present no serious obstacles to drilling. Below th is horizon th e form ations are predom inantly clays and m arly clays. This paper deals solely w ith problem s encountered when d rilling in these clays, p articu larly in th e deep wells (below 7000 ft.) where th ese problem s become acute. The difficulties m ay be sum m arized as follows :
(1) H igh viscosities, due p a rtly to th e n a tu re of th e form ation and p a rtly to th e high weights of m ud carried (110-150 lb per cu. ft).
Because of th e high weights m uds are very expensive to c o n tro l;
(2) Slow ra te s of p en etratio n . Average ra te s a t 4 f t per hour are quite common a n d th e y are sometimes m uch lo w er;
(3) Caving or squeezing form ation. This difficulty is not so universal as th e first tw o b u t is acu te in some areas.
These difficulties seldom become g reat enough to b ar fu rth er drilling progress, b u t th e y render wells tedious an d extrem ely expensive to drill.
Since th e y are due fundam entally to th e physico-chemical properties of clays it is along these lihes t h a t th e ir solution m ust be sought.
Relevant Clay Ch em istry.
Before going a n y fu rth er it is necessary to recap itu late briefly such properties of clays as affect these problems.
I t is now well established t h a t clays are definite crystalline compounds.
* P a p e r re a d before T rin id a d B ra n e h , I n s titu te o f P e tro le u m , M ay 1, 1946.
