Foliar Milstop Application Negatively Affects Soybean Aphid (Aphis glycines) Populations on Soybean (Glycine max)

The United States has harvested soybean (Glycine max (L.) Merr.) ever since its introduction in 1765 in Georgia. The soybean aphid (Aphis glycines Matsumura) first appeared in the USA July of 2000. Ever since then the soybean aphid has impacted soybean plant performance directly and indirectly resulting in an estimated $3.6 to $4.9 billion loss annually. Organic farmers have few options when trying to reduce soybean aphid populations on their crops. Potassium has been shown to reduce soybean aphid populations on soybeans.  Milstop is an 85% potassium bicarbonate, water soluble, broad spectrum, foliar fungicide that treats powdery mildew (Blumeria graminis (DC.) Speer), reduces aphid populations, and is certified organic. The purpose of this study was to determine if Milstop’s effect is due to potassium, bicarbonate, or both; whether Milstop affects soybean, soybean aphid, or both; and if any outside factors may influence cause and effect interactions. The purpose was tested using three treatments: purified water, Milstop, and Warrior (conventional insecticide) across both greenhouse and field studies. We have found that Milstop reduced aphid populations from 24% up to 46% and increased soybean yield by 48% compared to the water control. Milstop was not as effective as the Warrior control; 55%-90% less effective on aphid populations and 55% lower yield, but Milstop may serve as an option for organic farmers to keep soybean aphids below economic threshold.