Organic foliar MilStop shows efficacy against soybean aphid (Aphis glycines) on soybean (Glycine max)

Soybean (Glycine max (L.) Merr.) has been produced in the United States since 1765. Soybean aphids (Aphis glycines Matsumura) were first detected on soybean in the United States in 2000 and now cause an estimated yield loss of up to US$4.9 billion annually. Organic soybean producers have few insecticide products available for soybean aphid control. One product may be Milstop® (85 percent potassium bicarbonate), a broad spectrum foliar fungicide that is registered organic and has recently shown insecticidal properties, including efficacy against soybean aphid. The purpose of this study was to determine Milstop’s efficacy against soybean aphid in both growth-chamber and field-cage tests. In growth-chamber tests, Milstop’s active ingredient had no significant effect on soybean aphid populations but the product as a whole directly reduced soybean aphid populations by 94 percent after 48 hrs. In field-cage tests, Milstop non-significantly reduced soybean aphid populations from 24 to 46 percent compared to the water control and non-significantly preserved soybean yield by 48 percent. Although Milstop’s efficacy against soybean aphid was demonstrated, further study is needed to determine application schemes in which it can maintain soybean aphid populatons below the economically injurious levels in organic soybean and to isolate the ingredient(s) within Milstop that are responsible for efficacy against soybean aphid.