Friday, July 16, 2010

When it Comes to Soybean Aphid Saving a Pass Doesn't Necessarily Save you Money

Many growers are confronted with the following question.....

It is R1/R2 soybean and I am making my last glyphosate application. Should I tankmix an insecticide with my herbicide to clean up the few aphids I have in the field?

The answer to this question is rather simple....NO!!! Below Eileen Cullen our State Field Crops Extension Specialist explains why.

UW Entomology and IPM/entomology programs throughout the region do not recommend tank mixing insecticides for preventative aphid control in the absence of soybean aphid, or at soybean aphid numbers below the economic threshold of 250 aphids/plant. Insecticide premix products containing pyrethroid + nicotinoid active ingredients are asked about as potential 'insurance' treatment to use in a tank mix with fungicide before soybean aphids colonize a field or increase to economic threshold level. The foliar application of a nicotinoid has some translaminar systemic activity, but data on 30 days residual and 6 bu/acre yield assurances in the absence of economic threshold aphid populations have not been documented to my knowledge. Moreover, there is no assurance that a field treated preventatively would reach economic threshold if left untreated. There are many factors that determine this (timing of aphid colonization, weather, temperature, natural enemy (predator and parasitoid) suppression). We can expect some systemic activity with the nicotinoid class (whether applied as seed treatment, foliar, or in-furrow - depending on crop, soybean, potato, etc.). However, as the plant grows, active ingredient is translocated through the plant, but not all new growth retains that translocation throughout the life of the plant.

Regular field scouting and timing insecticide treatment to soybean aphid threshold is the recommendation in terms of efficacy, reliable yield protection, and cost to the grower. Systemic activity of a nicotinoid applied foliar would logically be best placed at a threshold-timed treatment in which the pyrethroid portion of the premix suppressed the aphid population at economic threshold of 250 aphids/plant, and any benefits of systemic activity from the nicotinoid could be retained following treatment. The pyrethroid broad spectrum activity will also kill natural enemies in the field, another reason the recommendation is to wait until aphid economic threshold to give natural enemies a chance to suppress populations. All the labeled insecticides will go a good job of controlling soybean aphid when applied at threshold. Regardless of insecticide material used, field scouting should continue through the R5 growth stage to monitor populations and effects of any previous insecticide treatments.