Manage grasses on rapeseed while limiting investment in seeding




Terranet Media

Pre-emergence weeding is often unavoidable, especially when growing grasses for which post-emergence weeding is not always sufficient. But many questions arise. How can this intervention be more successful and what is the technical and economic optimum if we want to limit seed investment?

Rapeseed plotBluegrass and ryegrass infestations are still progressing and becoming a priority target in farming systems. (© Terres Inovia)

Heavy infestations black grass and from ryegrass may limit crop biomass at the beginning of the cycle, which is nevertheless necessary for good plant behavior in the face of fleabane larvae.

In addition to everything agronomic levers known on the scale of crop rotation and inevitable (crop rotation with spring crops, stale beds, periodic plowing), necessarily, in rapegive due consideration to technical, economic and environmental issues related to grass care.

Avoid early post-emergence treatment against ryegrass

Use of Mozar/Belkar’s signature after the appearance solved problems in general dicotsespecially heavy infestations geraniums and from straws. This choice also eliminates investment in pre-emergence, a decision that is all the more motivated by the risk of drought that can lead to crop failure.

Dry soil conditions have encouraged growers to apply early post-emergence treatments with pre-emergence products such as Novall or Alabama at the first leaf cotyledon stage. In both cases, broadleaf weed control becomes more effective.

Check out the results of the survey conducted on terre-net.fr from 14 to 21 June 2022:

But just as with pre-emergence in dry conditions in early August, there is no grass care despite the use propizamide at the beginning of winter. Indeed, a failed pre-emergence treatment means that the graminicidal action will be based even more on propizamide (Kerb Flo, etc.), which can cause dissatisfaction and impact on water quality, which we want to limit as much as possible.

If a good level of effectiveness against foxtailprovided that the herbicide is based on metazachlor and that the treatment is carried out in early September, it is very different from ryegrass. Indeed, this grass sprouts very early, at the same time as rapeseed. Then the root and anti-germination effect of the herbicide on the weeds ceases at the time of germination.

Foliar graminicides are mainly used against cereals (when applied early about 2-4 leaves of rapeseed) or wild oats. Use on ryegrass and foxtail is a solution while it still works. This should be exceptional (recovering from failed precleaning) to prevent resistance calms down. In this case, and to reduce this risk, propizamide-based herbicides (eg Kerb, Ielo, etc.) are used. Herbicides based cletodym (Centurion, Ogive VXT, Foly R, etc.) are slightly less affected by resistance.

How to manage pre-emergence in dry conditions?

It should be remembered that napropamide (Colzamid and others) in preset included is by far the most effective solution against wheatgrass and ryegrass.

In herbicides, collected only chloroacetamides have an effect on herbs: metazachlor, dimethachlor, dmta-P and petoxamide. In pre-emergence and against foxtail, a drug based on metazachlor is indispensable (Novall, Alabama, Rapsan TDI, Sultan, Bandoneon, etc.).

Summary of seeding efficiency in couch grass and ryegrass based on Terres Inovia trialsSummary of seeding performance in couch grass and ryegrass based on Terres Inovia trials (©Terres Inovia)

When soil moisture conditions favorable for the effectiveness of root herbicides (rainfall in summer before application, possible rainfall after application), Terres Inovia trials show that foxtail and ryegrass infestations are reduced by 50–80%.

On the other hand, when terms are dry (before and after application) the efficiency drops sharply and ranges from 10 to 40%. So how to optimize the efficiency of these solutions?

To control foxtail, metazachlor-based pre-emergence preparations can be applied to early post-emergence rapeseed (rapeseed at the cotyledon stage, which begins to mark the row) and during the pre-emergence period of foxtail, i.e. in early September. In tests conducted by Terres Inovia in 2021 and 2022, delaying application saves 20 to 30 potency points on black grass.

With ryegrass, which sprouts at the same time as rapeseed, the situation is more delicate. in testimony Therefore, from pre-emergence to a more humid period is more dangerous. In the best case, even if seeding is done in early August in dry conditions, we will wait for the rains to return to apply a pre-emergence herbicide (quickly before rapeseed and ryegrass emerge). Then the herbicide will be more effective and persistent.

Reminder about rules and water quality:
From April 2021 terms of use metazachlor limit this active to a maximum application of 750 g/ha every 4 years or a maximum application of 500 g/ha every 3 years. The calculation is based on rapeseed crops in 2021.
The detection of active substances in water, such as metazachlor, dimethachlor, propizamide or their metabolites, is detrimental to the entire rapeseed industry. Everyone, from the clinician to the user, is responsible for ensuring the longevity of these highly strategic solutions, particularly in the fight against weed. To benefit from this tomorrow, it is important to respect good usage practices adapted to local conditions.

Limit investment to seeding to avoid losing too much in the event of a reversal

Faced with uncertainty about crop establishment (late emergence and early attack by adult fleas), it can be tempting to skip pre-emergence treatment and invest in herbicides only after the disease has been diagnosed. . It is very easy against broadleaf weeds, especially after mozzar has emerged.

However, dead end not recommended for medium or high grass pressure. Therefore, it is necessary to maintain the application before the appearance, but it is possible to optimize its application. As mentioned earlier, early post-emergence treatment is only possible when dealing with bluegrass.

Limiting investment to seed means choosing a very simple pre-emergence herbicide (or colsamide with a pre-emergence herbicide added) that remains optimal in grass control. On ryegrass, solutions based on metazachlor (Sultan, Rapsan, Springbok) or dimethachlor (Terox, Kolzor Uno) are preferred. On the foxtail, it is better to dwell on solutions based on metazachlor. Then the cost will be from 30 to 45 €/ha. The rest of the investment will be made after the installation is successful, against volunteer grasses, broadleaf weeds, or to “finish” grass control with propizamide (Kerb Flo, etc.).

Various strategies are shown in the table below. :

Canola Herbicide Application Strategies(© Terres Inovia)

Maintaining good conditions for the effectiveness of propizamide

This year there has been a lot of dissatisfaction with the effectiveness of propizamide. The first question posed is resistance. But in fact, no propizamide-resistant populations of wheatgrass or ryegrass have been found in field crops. Firm monitoring also points to this. Effectiveness defects are most often attributed to larger and more developed populations (thick root hairs, deep rooting) with propizamide in early winter.

Per optimize efficiency active substance, application should be carried out in moist and cool soil conditions (soil temperature < 10°C) in November (preferred) or even December, and on underdeveloped weeds. Best avoided before heavy rainfall to limit impact on water quality. Finally, you must know how to be patient, because the effectiveness of propizamide is a long-distance race. Efficiency is judged 3 months after application. In regulatory requirements, as in water quality matters, single use is the rule of thumb.

Another reminder of the rules:
In its technical instruction of May 27, 2021 “Controller’s Guide”, DGAL writes the following instruction: “The dose and the maximum number of applications apply to all commercial specialties, the composition of which is strictly identical. With the exception of special cases (), such cumulative use of FFPs containing the same active substance leads to an excess of the maximum authorized dose of use and, therefore, is not allowed. »
This means that no consecutive use of two propizamide-based products is allowed, even if these products have different MA numbers (eg Curb Flo then Barclay Propiz).

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