Reducing Fungicide and Herbicide Dosages
Ending systematic treatments and combining alternative techniques allow entering a logic of cost savings and reduction of phytosanitary products.
In this context, adjuvants are products used to improve the performance of phytosanitary products (retention, penetration and/or spreading) and reduce harmful effects such as runoff or drift.
Treatment strategy
A good treatment strategy is necessary to reduce herbicide doses.
- Adjuvantation of herbicides does not allow reducing the amount of active ingredient applied. A sufficient cumulative amount of active ingredient is necessary for good efficacy and persistence.
- Weed control failures are often linked to technical problems (incorrect dosage, forgetting adjuvants, products not adapted to weed flora) or practical issues (applications under poor climatic conditions, at an unsuitable weed stage, etc.). However, a good treatment strategy can lead to using doses lower than the authorized dose, while aiming for an optimum cleanliness objective.
- In general, it is more difficult to reduce herbicide doses than fungicide doses. This is especially true for weed control in cereals where root herbicides are used before weed emergence and/or on seedlings. Generally, adjuvants for root anti-grass herbicides have little interest, except to limit drift during spraying.
- Nevertheless, it is possible to consider a dose reduction for weed control in oilseed rape by applying micro-doses post-emergence, as practiced for example in weed control of beets. This requires good technical skills and also intervening under ideal treatment conditions, at the appropriate weed stage. Under these conditions, reductions of 10 to 25% are feasible.
Fungicide adjuvantation
It is one of the techniques to further reduce doses.
For fungicides, the contribution of adjuvantation to dose reduction can be around 15%. Several adjuvants can be combined with fungicides to optimize application efficacy. Most of these adjuvants have wetting, penetrating or fungicide retention roles on the leaf. Some adjuvants even combine several of these functions.
Humectants
They allow maintaining humidity on the leaf surface and thus prevent active ingredient crystallization and spray mixture evaporation. Commonly used is magnesium sulfate (EpsoTop).
The lower the humidity rate is, the more appropriate the use of a humectant is because it allows the sprayed droplet to remain longer on the leaf surface before evaporating, thus improving product penetration into the plant.
A minimum of 2% of the spray volume is recommended as a dosage for this adjuvant. It can be increased if humidity conditions become lower. However, note that a humectant will not compensate for fungicide efficacy loss related to too low humidity (< 60%) and thus poor spraying conditions.
Wetting agents
More expensive, wetting agents allow improving retention and spreading of spray droplets by reducing surface tension on the spray.
They are particularly effective for fungicides on peas and cereals (poorly wettable plants) or for anti-fusarium head blight treatment where the goal is to cover the ear.
Among them, commonly found are solutions from ACTION PIN based on terpenes such as HELIOTERPEN FILM at 0.4% of spray volume. It is authorized on cereals and has a wetting retention role. SILWET L77 at 0.05% of spray volume has a penetrating wetting role. It is authorized on wheat, barley, oats and oilseed rape.
Combination of techniques
To further reduce doses, or even eliminate synthetic fungicides, a more global strategy must be considered at the farm scale combining techniques:
- The variety mixing: in cereals, it is advised to combine at least 4 varieties to benefit from each one's advantages.
- Plant nutrition (sap analysis and application of trace elements): a well-nourished plant better resists diseases and pests and ultimately produces more with better quality. Sap analyses as agronomic management tools allow identifying deficiencies and excesses three weeks before the first visual symptoms appear. For cereals, three analyses are generally performed during a campaign: at tillering and/or regrowth, then at the 1 cm ear stage, or even at the last leaf stage to ensure final harvest quality.
- Applications of fermented extracts and/or oxygenated compost teas: used preventively, they stimulate the plant's natural defenses and reduce fungal pressure.
Sources
Does adjuvantation allow reducing fungicide and herbicide doses for the same efficacy?, AgroLeague
