Rola roślin wabiących owady w ochronie rzepaku Brassica napus L.

(1)

Daniel Nerad, Jan Vašák

Czech University of Agriculture, Prague

Role of attractive plants in oilseed rape

(Brassica napus L.) protection

*

Rola roślin wabiących owady w ochronie rzepaku Brassica napus L.

Ekologizace ochrany řepky ozimé (Brassica napus L.)

Słowa kluczowe rzepak ozimy, rzepik, szkodniki rzepaku, rośliny wabiące owady, obsiewy ochronne Key words: oilseed rape (Brassica napus), turnip rape (Brassica rapa), pests of oilseed rape,

plant attractants, protective sowings Praca dotyczy możliwości zmiany systemu ochrony rzepaku przed szkodnikami: chowa-czami (Ceutorrhynchus sp.) i słodyszkiem (Meligethes aeneus). W doświadczeniu polo-wym zastosowano rośliny wabiące owady do ich zwalczania – wysiewy bardzo wczesnych gatun-ków Brassica wokół pól rzepaku i niszczeniu owadów nalatujących na te obszary. Oceniono zdolność wabiącą bardzo wczesnych odmian rzepaku z odmianami rzepiku. Wyniki wskazują, że słodyszek i chowacz podobnik są bardziej wabione przez obszary rzepiku niż wczesnych odmian rzepaku. Stopień szkodliwości tych owadów został przekroczony jedynie na obsza-rach ochronnych. Obszary ochronne nie wabiły wczesnych szkodników to jest chowaczy: bruk-wiaczka i czterozębnego.

The work deals with the possibility of a change in the system of winter oilseed rape (Brassica

napus L.) protection against main insect pests:

from the Ceutorrhynchus sp., Meligethes aeneus. Plant attractants to insect were used in field experiments to control pests. Sowings of very early varieties from Brassica species around rapeseed fields and consecutive controls of pests on these preservative sowings. Difference between attractivity of very early varieties of oilseed rape (Brassica napus L.) and Brassica rapa L. varieties was evaluated. The results prove that Meligethes

aeneus and Ceutorhynchus assimilis are more

attracted by protective turnip rape plants (Brassica rapa) than by early varieties of oilseed rape Brassica napus. The harmful ratio of these pests to the oilseed rape was only exceeded in the protective sowings. The protective sowings did not show the attractivity for early pests C. napi and C. quadridens.

Introduction and work objective

The increase of the area of oilseed rape crop in the Czech Republic caused higher occurrence of insect pests. The stem weevils (Ceutorhynchus napi,

(2)

Ceutorhynchus quadridens), the pollen beetle (Meligethes aeneus), the cabbage

seed weevil (Ceutorhynchus assimilis) and the seed midge (Dasyneura brassicae) settle down on the plants during spring period and are the main insect pests. The earliest pests are C. napi and C. quadridens which injured the stems. M. aeneus usually injures the buds of oilseed rape. C. assimilis and D. brassicae attack young developing pods.

In the intensive agricultural production, two or three insecticide whole area sprays are used as a usual protection against these insect pests.

Some insect pests do not attack the whole oilseed rape plantation equally but prefer margin area. Reduction of insect pest population is due to the increasing distance from the field margins called “margin effect” (Vašák 1998).

Šedivý (1982), Krüger (1983) and Paul, Rawlinson (1992) recommend the insecticide treatment of oilseed rape field only on margins against M. aeneus and the other insect pests when the high density of insects occurs. The protection of highly attacked margins is evaluated by their function as the sources of insects and parazitoids of cardinal insect pests of winter oilseed rape (Šedivý 1983).

The possibility to control insect pests present in the margins sown with the plant attractants was observed in the field experiments in 1997. The plant attractants were sown around the fields together with oilseed rape. The aim of the work was chemical control of the pests just directed on these sowings. This method of protection could bring an appreciable economical and ecological effect.

In the field experiments in Sweden the mixture of oilseed rape with 2 or 4 per cent turnip rape (Brassica rapa L.) was evaluated on the treated and untreated experimental fields. Thereafter Nilsson (1996) suggested turnip rape as a plant attractant for liquidation of M. aeneus in spring rapeseed.

Büchi (1995) brings out that the mixture of turnip rape (5–20 per cent) and oilseed rape can be used for sowing of protective lines (5–6 m) around oilseed rape fields. The experiments did not show a clear preservative effect against

C. napi on the contrary with the occurrence of M. aeneus observed in 28.4–80.3 per

cent per one around sowing in the first days of an air raid. The method of preservative plant — lines could probably contribute to the increase of insect pest parasitoids as well.

Material and methods

The field experiments with protective sowings (with plant attractants) have been carried out since 1997. The protective belt of plant attractants against insect pests were sown around the margins of oilseed rape fields.

Turnip rape (Brassica rapa L.) variety REX was used as a plant attractant. This crop has the same seed composition and growing conditions as winter oilseed

(3)

rape. In 1998 and 1999 the experiment was extended by an extra early variety of oilseed rape — Prestol and spring oilseed rape.

The frequency of insect pests (M. aeneus, C. assimilis, D. brassicae) on the plants was observed in protective sowings and in different distances on the “cross-section” of experimental fields. The percentage of invaded stems and the level of damage (C. napi, C. quadridens) was also calculated.

“Natural method” — without a chemical treatment against insect pests, “current method” with 2–3 insecticide spraying and the method with spraying specially directed only on the protective sowings around fields were compared. The flight of insect pests was observed in yellow trap dishes located in the preservative sowings and in the whole crop area.

Results and Discussion

High invasion of beetles from Ceutorhynchus family (C. napi, C. quadridens)

was observed at the end of March at about 9oC. 10–12 beetles of the

Ceutorhynchus sp. were found in yellow traps. But in this period protective

sowings and crop were in the green bud stage with a little different phase of development. Therefore, the protective sowings could not yet act as “yellow” attractants for the earliest insect pests. In the “Natural method”, high percentage of stems attacked by the Ceutorhynchus sp. in the whole area of crops was found. On the contrary, the variant treated by Nurelle D (Pyrethroid + Organophosphate) approved a significant effect of sprays against insect pests (graph 1, 2).

The situation about 20. April is shown on the graph 3. In these days the temperatures reached 15°C and the invasion of M. aeneus culminated. There was a considerable difference between protective sowing of turnip rape and crop of rapeseed. Protective sowing was at the beginning of flowering and the crop was in the stage of green-yellow buds. The highest number of M. aeneus was in all cases on the protective sowing. The higher number of pests was also found on the opposite margin of the field. This margin was not protected by the protective sowing. This fact, such as at the C. assimilis could be partly explained by adjoining field of white mustard (Sinapis alba L.).

White mustard probably attracted the pests from the rapeseed. It could be considered an important fact that the highest amount of C. assimilis trapped also on the protective sowing (graph 4). The number of C. assimilis in the protective sowing of non-sprayed „natural“ method almost reached the harmful ratio — 1 beetle on 2 plants. The amount of these beetles considerably declined towards the middle of field.

(4)

sowing sowing)

wysiew ochronny bez wysiewu ochronnego

Distances from the margins on the cross selection of field [m]

Odległość od granic pola

27 15 9 29 6 13 6 0 1 1 3 1 1 2 0 10 20 30 40 50 60 70 80 90 100

5 m - Protective 25 m 50 m 125 m (middle) 50 m 25 m 5 m (without

0 5 10 15 20 25 30 35 40 45 50 % of infested stems feeding tunnel (cm) % of infested stems % porażonych łodyg feeding tunnel [cm] kanały po żerowaniu aver ag e l e n g th of fee d ing t unn el [cm ] śre d n ia d ług o ść ka na łó w po żer ow ani u % o f inf e s te d s te ms — % por a żonyc h łody g

Graf 1. Per cent of stem infestation by Ceutorhynchus sp. and average length of feeding tunnel at 100 plants; TURSKO — 3.6. 1998 (with spraying) — Procent łodyg porażonych przez chowacze

i średnia długość kanałów po żerowaniu na 100 roślin (przy stosowaniu oprysków insektycydami)

sowing sowing)

Odległość od granic pola

97 97 81 88 94 100 100 24 20 28 13 25 20 29 0 10 20 30 40 50 60 70 80 90 100

5 m - Protective 25 m 50 m 125 m (middle) 50 m 25 m 5 m (without

0 5 10 15 20 25 30 35 40 45 50 % of infested stems feeding tunnel (cm) aver ag e l e n g th of fee d in g t unn el [cm ] śre d n ia d ług o ść ka na łów p o ż er ow ani u % o f inf e s te d s te ms — %p o ra żonyc h łody g

Graf 2. Per cent of stem infestation by Ceutorhynchus sp. and average length of feeding tunnel at 100 plants; TURSKO — 3.6. 1998 (without spraying) — Procent łodyg porażonych przez

(5)

Protective sowing sowing)

Odległość od granic pola 361 134 198 70 118 236 260 101 42 109 60 94 116 132 56 231 99 104 0 50 100 150 200 250 300 350 400 5 m - 25 m 50 m 100 m 125 m 100 m 50 m 25 m 5 m (without number of beet les a/ without spraying b/with spraying without spraying bez oprysku insektycydem with spraying z opryskiem insektycydem num ber o f b eetl es — liczba c hrz ą szczy

Graf 3. Number of Meligethes aeneus on main stem of 100 plants; TURSKO — 21. 4. 1998; (turnip rape: beginning of full bloom, rapeseed: yellow buds — beginning of bloom) — Liczba słodyszków

rzepakowych na głównym pędzie 100 roślin (rzepik — początek kwitnienia, rzepak — żółte pąki — początek kwitnienia)

Protective sowing sowing)

Odległość od granic pola 15 10 7 0 2 26 35 5 2 9 9 5 45 1 7 1 0 0 0 5 10 15 20 25 30 35 40 45 50 5 m - 25 m 50 m 100 m 125 m 100 m 50 m 25 m 5 m (without a/ without spraying b/with spraying without spraying bez oprysku insektycydem with spraying z opryskiem insektycydem num ber of b eetl e s — liczba c hrz ą szczy

Graf 4. Number of Ceutorhynchus assimilis on main racemes of 100 plants; TURSKO — 30.4.1998; (turnip rape: full bloom — ending of bloom, rapeseed: beginning of full bloom) — Liczba chrząszczy

chowacza podobnika na głównych kwiatostanach 100 roślin (rzepik — pełnia kwitnienia — koniec kwitnienia, rzepak — początek pełnego kwitnienia)

(6)

Conclusions

The observed results of the experiment show that the first flight of M. aeneus could be considerably trapped by a protective sowing. The protective sowing is also very attractive for C. assimilis. The number of beetles was the highest just in the protective sowing in all experiments. The attractivity could be partly suggested also for Dasyneura brassicae. The influence of protective sowing on the infestation by C. napi and C. quadridens was not proved. The high number of infested stems in all distances from the field margins (was observed in the non-sprayed combination — natural method).

The obtained results suggest that the pests are preferably attracted by specific host plant odour more than by the yellow colour of flowers. The distinct odour of many Brassica species is based on a different glucosinolate content and its split products. That could explain a better attractivity of turnip rape in comparison with an early flowering rapeseed variety.

References

Bezecná, O. Vašák, J. 1988. Biologizace ochrany repky - záchytné obsevy. Úroda, 7: 326–327. Büchi, R. 1995. Combination of trap plants (Brassica rapa var. silvestris) and insecticide use to

control rape pests. In IOBC-WPRS Working Group 'Integrated control in oilseed crops' held in Zurich, Switzerland, on 24-25 February 1994. Bulletin-OILB-SROP. 18: 4, 102-121; 14 ref. Fábry, A. a kol,. 1992: Olejniny. MZe CR 1992.

Jankowski, K., Budzynski, W., 1997. Zemedelské dopady pri vynechání insekticidu u repky ozimé. In: Systém výroby repky. 14. sborník SPZO Praha, Hluk 18-20.11. 1997.

Kelm, M., Klukowski, Z. 1999. Harmfulness of the stem weevil (Ceutorhynchus pallidactylus) in the aspects of oilseed rape yielding physiology. In: Working Group on integrated Control in Oilseed Crops. 9th Biannual-Meeting, CZU Prague. 31.5. – 2.6. 1999.

Nilsson, C. 1996. Integrated control of pests in oil plants - trap crops for pollen beetles in spring rape. Agriculture – pests, diseases and weeds. 37th Swedish Crop Protection Conference, Uppsala, Sweden, 26-27 January, 105-112; 2 ref.

Paul, H, V. 1988. Krankenheiten und Schädlinge des Rapses. Thomas Mann Verlag. Gelsenkirchen – Buer.

Šedivý, J. 1983. Tersilochinae as parasitoids of insect pests of winter rape (Hymenoptera, Ichneumonidae), Contrib. Amer. Ent. Inst. Vol. 20: 266-276.

Šedivý, J. 1982. Okrajové ošetrení porostu jako úsporné opatrení v ochrane proti škudcum. Úroda 5: 233–235.

Vašák, J. a kol. 1997. Systém výroby repky. ceská a slovenská pestitelská technologie ozimé repky pro roky 1997-1999. Praha.

Vašák, J. a kol., 1988: Systém výroby repky. Metodika ceskoslovenske pestitelské technologie ozimé repky na období 1988-1990. MZVž cSR.