ABSTRACT

Today, chemical inputs are a necessary condition for a sustainable production of winter oilseed rape. CETIOM contributes to elaborate recommendations for farmers to optimize their practices, avoid useless treatments and - recent concern - respect environmental constraints. A better knowledge of real plant protection practices seems to be the only way for new progress. A study was performed in a traditional and still important zone of rape production - Champagne berrichonne - in collaboration with a group of 23 farmers (1996-97) reduce to 17 farmers (1997-98). Considering the number of treatments, farmers applied few products (1996-97 : 7.6 ; 1997-98 : 8.0), but at least more that would totalize an adept of ``good plant protection practices'' (2 herbicides, 1-3 insecticides; 1 fungicide). Annual variations are preponderant, i.e., the period did not request large uses of molluscicides, in spring 1998, strong aphid attacks generated a supernumerary insecticide ... In this context : (1) Herbicides are managed as recommended (trifluralin, metazachlor) ; (2) in autumn, insecticides are sprayed rather without good adequation between dates and target pests ; (3) in spring, insecticide (stem weevils) and fungicide (stem blight) applications tend to be better positioned but useless treatments intervene again. Some chemicals are not applied in accord with registered uses. This study allows us to consider new possible improvement of plant protection practices. First our present knowledge has to be valorized.

INTRODUCTON

Today, chemical inputs are a necessary condition for a sustainable production of winter oilseed rape. CETIOM contributes to elaborate recommendations for farmers to optimize their practices, avoid useless treatments and - recent concern - respect environmental constraints (Anonyme, 1998). A better knowledge of real plant protection practices seems to be the only way for new progress.

MATERIALS AND METHODS

The study was performed in a traditional and still important zone of rape production - Champagne berrichonne - in collaboration with a group of 24 farmers (1996-97) then 17 farmers (1997-98) and its local technical staff (Chambre d'agriculture de l'Indre).

Farmers had to transcript in detail their phytosanitary practices and to give basic information on one rape field per year. All these elements gave matter of critical discussions with local techniciens.

To manage oilseed rape protection farmers have the possibility to complement their own knowledge of the crop with technical documents - i. e. : leaflet from CETIOM (Anonyme, 1998) - to consult different advising messages or to question different technical staffs. A compilation of all these sources of information have been performed. All these explicative elements have been comforted by fields observations (spring 1997 : 9 fields , 1997-98 : 8 fields).

RESULTS.

Actual rape cultivation request pesticide use : herbicides, insecticides and molluscicids, fungicides and growth regulators (Trift, 1998).

1 HERBICIDES

In France, weed control is based on pre-sowing - pre-emergence treatments, often a combination of two sprays. Usually, post-emergence herbicides are only applied to solve specific difficulties or to supply previous herbicides lakes of efficacy.

Table 1 - Herbicides (number of fields).

		1996	- FS	+ FS	1997	- FS	+ FS
	Pre-sowing	8	1	7	5	4	1
	Pre-emergence	2	1	1	1	0	1
	P-s + P-e	14	6	8	11	3	8
		24	8	16	17	7	10

with (+ FS) or without (- FS) post-emergence treatment (FS : foliar spray)

Control of weeds is especially based on pre-sowing treatment with trifluralin (1996 : 22 fields, 1997 : 15 fields) and metazachlor (1996 : 15 fields, 1997 : 9 fields). But, a post-emergence treatment is often applied (1996 : 15 fields ; 1997 : 10 fields). So, an average of 3 herbicides is usual (1996 : 66 herbicides, 1997 : 47 herbicides).

2 INSECTICIDES

Concerning insect pests, risks do not concretize every where every year. As a long list of potential pests is associated to oil seed rape, farmers have not the possibility to link each pest with a treatment or to practice systematic control.

Farmers use certified seeds often treated (insecticide : mercaptodimethur or isophenphos, fungicide : thirame). The efficacy of such treatments is not decisive for the protection of the young crops.

General autumnal protection against insects can come from microgranulated insecticide localized with the seeds in the furrow (1196 : 1 field, 1997 : 0 field). To day farmers prefer controls based on foliar sprays.

Table 2 - Control of insect pests in autumn.

		1996	1997
	Number of sprays	0 1 2 3	0 1 2 3
	Number of fields	6 12 4 1	4 9 2 1

In autumn, without major difficulties, fields can remain untreated but the rule is in spraying one to three times

Giving priority to other works on the farms (cereal sowing, maize harvesting), farmers are not in situation to manage autumnal rape protection (Tchobanian et al., 1998). Chemicals are applied when possible not when really need. In this context, in intermediate conditions of temperature and humidity, pyrethroid insecticides - giving long protections - appear well adapted. So it is somewhat surprising to constat the large part done to parathion (1996 : 19 parathion for 21 sprays) and to sprays combining parathion with a second insecticide. Choices of chemicals are not always in accord with registration rules.

In spring, farmers are invited to take special care of stem weevils (Ceutorhynchus napi GYLL). Themselves seem to be attentive to blossom beetle (Meligethes sp.). Thus a fungicide is applied on flowering crops (sclerotinia) adjunction of an insecticide for seedpod weevil (Ceutorhynchus assimilis PAYK.) is not a rule. An unexpected difficulty, like aphids in 1998, can be taken in account.

Table 3 - Control of insect pests in spring (number of fields treated)

	1997	1998
Stem weevil Blossom beetle Seedpod weevil Mealy cabbage aphid	23 9 2 0	14 4 1 12
Total fields	24	17

Pyrethroids fit well to control coleopteran species. Parathion is still used. Confronted to aphids farmers change for better adapted products (1998 : 9 triazamate, 15 aphicids, 16 treatments against aphids).

3 MOLLUSCICIDES

1996 and 1997 were not years favorable to slugs and fields were not damaged. The strategy which consists in application of baits on the soil at sowing time had been put in practice for 3 fields in 1996 and 1 field in 1997. This strategy is theoretically restricted to risky fields, what is not easy to define. One farmer applied a molluscicide on a crop damaged - but not by slugs - after emergence. Treatments restricted to the borders of the fields are not unusual (1996 : 5 fields, 1997 : 3 fields).

4 FUNGICIDES

In autumn fungicides sprays are not usual but, after some questions about phoma from the previous year, some farmers have prefered to spray (1996 : 3 fields, 1997 : no treatment).

Table 4 - Fungicide sprays in spring (number of fields).

	1997	1998
Number of treatments	0 1 2	0 1 2
cylindrosporium sclerotinia alternaria	20 4 0 6 17 1 20 4 0	13 4 0 1 15 1 15 2 0

In spring, farmers are sensibilized to diseases and especially to stem blight (sclerotinia) hich is considered as a major risk for the crop. Results for 1996 are linked to a context of extreme dryness for flowering.

5 GROWTH REGULATORS

Farmers are not inclined to recourse to growth regulators. Some attempts to use fungicides as growth regulators are observed.

Table 5 - Spring regulation of winter oilseed rape growth (number of fields).

		1997	1998
	1 spray : growth regulator (GR) 1 spray : fungicide (as GR) 2 sprays : GR + fungicide (as GR)	5 2 1	2 1 1

Annual variations are preponderant, i.e., the period did not request large uses of molluscicides, in spring 1998, strong aphid attacks generated a supernumerary insecticide ... In this context : (1) Herbicides are managed as recommended (trifluralin, metazachlor) ; (2) in autumn, insecticides are sprayed rather without good adequation between dates and target pests ; (3) in spring, insecticide (stem weevils) and fungicide (stem blight) applications tend to be better positioned but useless treatments intervene again. Some chemicals are not applied in accord with registered uses.

6 PLANT PROTECTION PRACTICES

Farmers practice an average of 6.05 - 6.40 sprays to apply 7.6 - 7.9 pesticides - herbicides, insecticides (+ molluscicides), fungicides and growth regulators - on a winter oilseed rape crop.

Table 6 - Winter oilseed rape crop protection.

	1996 - 1997	1997-1998
	Treat Treat Prod. Prod. number mean rnumber mean	Treat Treat Prod. Prod. number mean rnumber mean
Autumn Spring Total	7.9 3.3 9.8 4.1 6.6 2.7 8.5 3.5 14.5 6.0 18.3 7.6	5.6 3.3 6.8 4.0 5.3 3.1 6.7 3.9 10.9 6.4 13.5 7.9

Treat. : treatments, Prod. : chemical products.

Table 7 - Plant protection practices (number of chemicals applied).

		1996-1997	1997-1998
	Herbicides	2.8	2.8
	Others Autumn	1.3 4.1	1.2 4.0
	Insecticides (stem weevil) Fungides (sclerotinia) Insecticides (aphids) Others Spring	1.5 1.0 0.0 1.0 3.5	0.9 1.1 0.9 1.0 3.9
	Total	7.6	7.9

CONCLUSION

Considering the number of treatments, farmers applied few products, but at least more that would totalize an adept of ``good plant protection practices'' (2 herbicides, 1-3 insecticides; 1 fungicide).

This study allows us to consider new possible improvement of plant protection practices. First our present knowledge has to be valorized.

(1) The number of treatments is not so important regarding the difficulties to solve. We certainly have to consider farmers are not in good conditions to decide to spray or not to spray. A posteriori, it is rather easy to give an argumentative advice on their practices. A priori, more useful advises are needed.

(2) But some treatments are not justified by effective risks for the crops. Actual available information have to be put disposable for farmers in a better way.

(3) But some treatments are not applied in the best conditions of efficacy. Especially in autumn and against insect pests, insecticides are applied several weeks before or after the optimal date. Basis of integrated pest management are not applied.

(4) But some choices of chemicals do not suit with registration rules. We must help farmers to put themselves in mind of better respect of laws taking first in account a better respect of the environment.

Confronted to an unexpected difficulty, like aphids in spring 1998, farmers reacted by well fitted control measurements (timing of treatments, choice of products). So, in the same manner, they certainly can revise their actual practices.

References

1. Anomyme, 1998. Colza d?hiver, les techniques culturales, le contexte economique. Edition Cetiom, mai 1998 : 38 pp.

2. Tchobanian A., Sébillotte C., Ballanger Y., 1998. Traitements colza. Comprendre les modes de décision en culture. Oléoscope, 47 : 29-31.

3. Trift A., 1998. Diagnostic des pratiques phytosanitaires sur colza d'?hiver dans l?'Indre. DESS, Faculté d?Histoire-Géographie d?'Amiens : 150 pp.