What effects do recent rains have on soybean aphid?
Thunderstorms with heavy downpours have caught the news over the last two weeks. Anecdotal observations indicate heavy, driving rains (>1″) on small soybean plants can drastically reduce aphid populations. These observations are backed up research with a rainfall simulator that found a 45% reduction in aphid populations 5 days after a 2″ rainfall on V3-V4 soybean. The direct effect of rain diminishes as soybean plant size increases. Areas with heavy early season rainfalls are less likely to have large aphid populations first. With colonization from buckthorn nearly complete, later occurring infestations may still develop because of aphid immigration from other areas with less rainfall. Rainfall may also enhance activity of aphid-attacking fungi and relieve drought stress on soybean (reducing the nutritional quality of the plant to aphids). When should soybean aphid scouting start? Historically, scouting on a widespread basis before the end of June has not been needed in Minnesota. Soyb
