If the root products above all require moist soil to homogenize the product, they are not sensitive to the volume of mixture and the type of nozzle used. It is quite the opposite for contact products such as pyrethroids targeting fall aphids.
The quality of spraying must be taken into account for insecticides
THE 2021 essays on prosulfocarbe clearly showed that air injection nozzles could be used, regardless of the volume of spray, with root herbicides. They are therefore to be preferred for, the least, reduce driftbut also limit the volatilization of these products to the ground. Remember that they are even mandatory for the application of prosulfocarb.
Review on Arvalis: “ Prosulfocarb: carefully follow the application rules to weed cereals »
As for insecticides from the pyrethroid family, which act mainly by contact on the target, few references exist on the subject. But tests carried out with the ITB in 2022 on contact herbicides clearly show that the quality of spraying influences their effectiveness.
By testing three volumes of mixture and four types of nozzles (one classic slot nozzle and three air injection nozzles), we clearly see an effect of the two factors studied. At 50 l/ha and 80 l/ha, only the classic slot reference nozzle gives satisfactory results, while at 150 l/ha, air injection nozzles approved at 66% and 75% reduction in drift can be used. The 90% approved nozzle produces drops that are too large for a contact product.
Different technical positions
On the other hand, it is important to remember that pyrethroids are not effective in the case of preventive application. They must be applied as soon as aphids are actually observed in the plot.
For their part, root herbicides are constrained by a limit stage of application (3 leaf stage of the cereal in the case of prosulfocarb) and prefer moist soil conditions to maximize their effectiveness.
In fact, the positioning of the herbicide treatment rarely coincides with the optimal insecticide treatment date. We therefore understand that mixing is difficult to achieve if we want to maximize efficiency on the two intended targets (grasses on one side, aphids/leafhoppers on the other).
What to do in case of mixing?
If, during the herbicide application, the pest pressure present in the plot also justifies the application of an insecticide, the mixture must be applied at a minimum of 150 l/ha and only with air injection nozzles at 66 % or 75% to maximize the effectiveness of both products.
But, in most situations, it is appropriate to separate the applications to use as much as possible a nozzle approved at 90% with prosulfocarb, an obligation to reduce the safety distance from local residents to 10 meters instead of 20m by default. However, such a nozzle should be avoided for contact insecticides.
Read also > Fall cereal sowing: making the right choices
Author: Benjamin Perriot (Arvalis).
