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Pilorgé E. , Gigandon C.

CETIOM, BP n°4, 78850 Thiverval-Grignon - FRANCE. e.mail:


This evaluation deals with technical, organizational and environmental aspects of the introduction of GMO herbicides resistant oilseed rape varieties in French cropping systems. This complex question requires knowledge on the behavior of these herbicide- resistant oilseed rape systems at short and medium range (stability of these systems), and on the actual cropping systems.

In terms of weeding techniques, the impact must be appraised with regard to advent floras and present weeding techniques. At this level, herbicides tolerant varieties may give solutions for some specific problems. The proper characteristics of the herbicides lead to immediate advantages concerning their practical effects (high level for immediate efficacies, broad spectrum) but also disadvantages compared to present techniques (no persistent activity). Questions remains about the technical durability of these herbicide-crop tolerant systems and the needs of specific management.

Regarding the works organization at farm level, using post-emergence herbicides would allow to facilitate the sowing phase, compared to the present pre-emergence herbicides with soil incorporation. The simulations show that the side effects on the sowing dates and works organization for the other crops would be limited. Concerning the environmental effects, the general tendency is rather favorable, due to the characteristics of the active ingredients.

KEY WORDS: oilseed rape, GMO, herbicides, flora, farm organization, environment.


The studies on the weeds flora of OSR crops, on weeds control present practices and the first observations on the OSR herbicide tolerant systems in experimental conditions allow to examine the potential impacts of these GMO herbicide tolerant crops on weeding techniques, farms organization and costs, environmental fate.

1. The advent flora of oilseed rape crops in France

The flora encountered in oilseed rape crops are the result of the pedological and climatological context, of the cropping systems and present and past agricultural practices. For about 20 years, regional problems for particular weeds species have appeared, as symptoms of advent floras evolutions. The origins of these evolutions seem to lies among the following causes:

- the short rotations and frequent returns of OSR on the same field;

- the use of a quite limited number of active ingredients for chemical weeds control;

- the evolutions of agricultural practices: earlier sowings, increase of reduced tillage practices (without deep plowing);

- the lack of efficacy of the current OSR herbicides on a part of the flora, and the misuse of herbicides doses reduction. Repeated insufficient efficacies led to the development of geranium sp, papaver rhoeas, and brassicaceae weeds.

- the extension of uncultivated fallows following the first reform of European Common Agricultural Policy in 1992, which also favored the extension of geranium species and brassicaceae weeds.

2. Present flora and interest of new solutions

Among the whole flora, one must distinguish:

- a majority of weeds species well controlled by the current herbicides alone or in programs,

- some species for which pre-emergence herbicides exist, but insufficient or irregular, and without possible post-emergence herbicides solutions: geranium species, sinapis arvensis, sisymbrium officinale, euphorbia sp....

- at last, some species for which no chemical solution exists, either as pre-emergence or post emergence herbicides: barbarea intermedia, calepina irregularis, lepidium campestre, viola arvensis, etc...

The weeds of the last two categories may be locally important, due to short rotations. Some of them cause growing problems. The predominance in the previous species of weeds of the same family as OSR (brassicaceae) must be noticed: sinapis arvensis, sisymbrium officinale, barbarea intermedia, calepina irregularis, lepidium campestre. Infestations of brassicaceae or geranium may forbid OSR crops in heavily infested fields.

The possibility to use post emergence herbicides to control those species would be in fact an important technical improvement, whatever the nature of the solutions.

The first experimental references obtained in CETIOM on OSR crops tolerant to glyphosate and glufosinate show satisfying practical efficacies for the main weed species mentioned above, except viola arvensis. The control of geranium sp. would be possible by glufosinate, and by glyphosate, if herbicides rates are properly adjusted and treatments conditions are optimized. Double sprays could be necessary to control these species, particularly in case of progressive emergence.

3. Present weed control practices in France

In present conditions, OSR weeds control is globally mastered with a limited set of herbicides, broad spectrum (but not complete), mainly applied pre-sowing or pre-emergence.

Post-emergence herbicides are few, except against monocotyledons, and generally expensive: OSR weeds control costs varies from 54 to 92 Euros/ha and may reach 150 Euros/ha in the most critical situations.

CETIOM surveys show significant differences in weeds control strategies among the French regions (table 1).

Table 1 :Main weeding programs for winter rapeseed in France and main production

regions, in % of cultivated acreage








pre-sowing herbicides only






Program pre-sowing + pre-emergence






Program pre-sowing + post-emergence






Program pre-sowing + pre-emergence + post-emergence






pre-emergence herbicides only






Program pre-emergence + post-emergence






post emergence herbicides only






without chemical weeds control






(Source : CETIOM, 1996)

In the East of France, where OSR is frequently the unique possibility as profitable head of rotation, farmers choose preferentially the most regularly secure solutions: programs adding pre-sowing and pre-emergence herbicides. Pre-emergence herbicides alone represent a relatively small part of the acreage in this region: less than 10% compared to a national average of 20%. Complex programs (pre-sowing + pre-emergence + post-emergence) are quite important in Lorraine, with 15% of the acreage, as basic herbicides or programs reveal inefficient and must be reinforced by a post-emergence herbicide, when an efficientone exists...

In this region, the use of herbicides against monocotyledons specifically (mainly against cereals volunteers) is rather important with 6% of the acreage, mainly as foliar contact herbicides.

In Burgundy, pre-emergence herbicides alone are more important, on about 20% of the acreage. Post emergence herbicides are used against monocotyledons, geranium sp. and galium aparine.

In Centre region, the solutions are more diversified: acreages controlled by programs adding pre-emergence to pre-sowing (30%) are similar to acreages with pre-emergence herbicides alone (25%). The main other programs represent about 10% of the acreage each. Post emergence herbicides are involved in 34% of the programs, against monocotyledons, matricaria sp, apiaceae and brassicaceae families, which may be locally important.

The same tendency is observed in Poitou-Charentes (West of France) for the same reasons: post emergence herbicides are used on 47% of the acreage, mainly against brassicaceae weeds.

4. Technical interest of the replacement of present weeds control programs by herbicides tolerant OSR systems.

The present weeds control programs could be classified according to their complexity, i.e. the difficulty to control the present flora and so, the greater interest to replace them by broad spectrum herbicides tolerant OSR systems.

Programs including a post-emergence herbicide after a first component pre-sowing + pre-emergence (10%) or pre-emergence (7%) represent 17% of the national acreage. The supplementary post emergence herbicide may be either a part of the scheduled program to fight against a specific weed (brassicaceae, geranium, monocotyledons, etc...), or added as a secondary solution to compensate failures or irregularities of the basic schedule, when it is possible.

Consequently, we can estimate that broad spectrum herbicides tolerant OSR systems would give solutions for situations infested with weeds complex hardly controlled by simple available herbicides at present time, on 10 to 20% of the OSR acreage in France.

Classical programs - pre-sowing + pre-emergence (40%) and pre-emergence alone (20%) permit a satisfying weeds control for about 60% of the acreage. Those situations, without any post-emergence herbicide may be considered as generally controlled. Nevertheless, for a part of them, the absence of post-emergence spray might be due to the lack of efficient solution. The weeds control level could be improved and justify a shift to a more efficient technique.

On this part of the OSR acreage, farmers will be interested by herbicides tolerant OSR systems if these systems are competitive from the technical, practical (better work organization on farms, decrease of work peaks...) and economical (lower cost) points of view.

At last, the remaining part of the acreage (20%) are managed either with a pre-sowing spray (mainly trifluralin), followed or not by a post-emergence spray in case of latter weeds problems or with a post-emergence spray only.

Several interpretations are possible:

- the will to reduce costs: minimal investment before crop establishment;

- the fear, in case of bad crop establishment or consequent autumn problem, to limit the possibilities to replace OSR by another crop;

- problems of simple floras including a limited number of weeds species not controlled by pre-sowing and pre-emergence herbicides (case of many brassicaceae weeds).

The possibilities offered by the broad spectrum herbicides tolerant OSR systems could give solutions in the last two cases: no residual effect for the glyphosate, glufosinate and ioxynils, efficacy on the considered species). The cost of these systems will be deciding in the first case.

We can conclude that a high technical interest for broad spectrum herbicides tolerant OSR systems on 20% to 30% of the OSR acreage seems to be realistic, at least in a first period (in fact, we did not take into account the possibilities of efficacy decreases of these systems due to the possible development of resistant floras, with needs further studies). In other situations, the comparative cost of the available solutions and the limits of the herbicides tolerant OSR systems (no persistence, more or less convenient changes in works organization...) will be deciding factors.

5. Impact on works organization

The shift from practices based mainly on pre-sowing and pre-emergence herbicides to a complete post emergence management will induce significant changes on works duration and periods on the OSR crop.

This shift could be particularly convenient for the great farms based on cereal cropping (OSR-wheat-barley or OSR-wheat rotations) which know major working peak periods at the time of OSR soil preparation and sowing, including pre-sowing sprays with soil incorporation and pre-emergence spray. The saving in time due to the cancellation of herbicides sprays represents about 6 to 12% of the total working time on this period which is, in French conditions, a key period for OSR crop establishment, where limited delays in sowing dates may lead to disastrous consequences.

The difficulties for weeds control with the present solutions are a technical obstacle to the development of simplified soil preparation techniques, without plowing. The herbicides tolerant OSR systems could facilitate the implementation of these techniques, by limiting weeds control problems (at least in a first time: simplified soil preparation may induce an increase in weeds seeds quantities in the surface layer of the soil) and could allow to add the very important working time reduction due to simplified soil preparation, to a less important time saving due to the cancellation of pre-sowing (incorporated) and pre-emergence sprays. The saving in time on the sowing period would permit to optimize sowing dates and limit late sowings, which are the origin of crops failures or reduced potentials.

Theses advantages are balanced by some potential disadvantages: farmers will have to manage OSR weeds control during a period which is normally devoted to cereals sowings. Working time and meteorological simulations show that herbicides tolerant OSR systems introduction will have few consequences on cereals sowing dates when OSR herbicides sprays are made in priority in case of concomitance of OSR sprays and cereals works. At the opposite, if priority is given to cereals works, OSR herbicides sprays could be delayed after the suitable period for optimal efficacy.

6. Long term impact on cropping systems

Main questions come from:

- the possibilities of efficacy decrease of the herbicides used in tolerant OSR systems, if weeds species get herbicide resistance genes (gene flow to the brassicaceae weeds) or due to the adaptation of some species to the recurrent use of the active ingredient. The herbicides tolerant OSR systems duration is still to be evaluated.

- the necessity to manage herbicide tolerant rapeseed volunteers in the different crops of the rotations, in fallows, in non agricultural lands. These volunteers will require a specific management when the other crops of the rotation use the same active ingredients as those uses in rapeseed crops. The case of intercropping periods must be considered too: the active ingredients used in herbicides tolerant OSR are sometimes used for weeds management during intercropping periods (glyphosate) and will have to be complemented with other active ingredients: it may induce consequences on the total quantities of active ingredients sprayed in the environment, on global weeds control cost, on the following crops if the complementary active ingredients are persistent.

7 Impact on the productions costs

The marketing of herbicides tolerant OSR would probably be followed in a first time by a decrease of herbicides costs and by an apparent decrease of weeds control cost. The calculation of the real weeds control costs variation will have to include other elements such as seeds cost (including the impossibility to use on farm produced seeds), yields of the varieties, etc... The potential consequences of the introduction of the new technique on other points of the cropping systems could a priori affect the long term advantages.

8 Impacts on environmental fate

The change from classical systems to herbicides tolerant OSR systems will induce changes in the nature of the active ingredients and in the global quantities spread in the environment. If OSR crop only is taken into account, the introductions of the new systems would allow to reduce by 25% to 25% the total quantity of active ingredients, depending on the weeds control program which was used before, in favor of active ingredient of better ecotoxicological and environmental characteristics (glyphosate, glufosinate). The impact of potential use of complementary active ingredient for miscellaneous uses (other crops, intercropping, ...) will have to be considered.


The possibility to use broad spectrum herbicides tolerant OSR systems is an attractive perspective to face specific problems encountered in weeds control with presently available herbicides. As any weeds control techniques, these systems will show advantages and disadvantages, different from those of the present techniques. It will be necessary to manage for the best the whole set of available technical solutions, classical and new, according to the farming constraints, in order to limit the potential undesirable effects on the whole cropping system, and ensure the durability of the new solutions.


1. OWEN M D K. North American developments in herbicide tolerant crops. Brighton BCPC Weeds Conference, 1997.

2. MESSEAN A. Management of herbicides tolerant crops in Europe. Brighton BCPC Weeds Conference, 1997.

3. COLBACH N, CLERMONT C, MEYNARD J M, MESSEAN A. Modélisation de l'effet des pratiques culturales sur la dissémination des repousses de colza résistantes à un herbicide: le logiciel Genesys. Seventeenth COLUMA Conference International Meeting on Weed Control. Dijon France 1998.

4. DARMENCY H. Questions à propos des variétés résistantes à un herbicide. Seventeenth COLUMA Conference International Meeting on Weed Control. Dijon France 1998.

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