Foliar Fertilization Does Not Reduce Soybean Aphid Populations, Change Plant Nitrogen and Potassium, or Protect Yield from Aphid Feeding, under Non‐limiting Nutrient Conditions

Abstract

The soybean aphid (Aphis glycines Matsumura) is a key pest of soybean [Glycine max (L.) Merr] in the Midwest. In the early 2000s, foliar fertilization was sometimes recommended to reduce aphid populations, regardless of soil or plant nutrient levels in fields. Nitrogen (N) fertilization or potassium (K) deficiency can increase aphid populations, so the impact of foliar fertilization on soybean aphid was not clear. This study measured percent N and K in leaf tissue, cumulative aphid days, and yield in aphid‐free (insecticide treated) and aphid‐infested soybean plots, with or without a foliar fertilizer timed at the R3 and R5 growth stages during typical peak aphid infestation. Five separate trials were done over 2 years in non‐deficient fields. In a low aphid year (2004), fertilization did not increase percent N and K in leaf tissue, change aphid numbers, or effect yield. In an aphid outbreak year (2005), percent N and K was significantly lower on three occasions in aphid‐infested treatments. Significant reductions in aphid number and increases in yield were measured at all locations in 2005, the result of insecticide (not fertilizer) application. In a laboratory assay, aphid survival and nymph production was not affected by direct exposure to fertilizer diluted to a field rate. This study cannot rule out the possibility that in nutrient‐deficient fields, foliar fertilization may alleviate stress on aphid‐infested plants. However, given the high reproductive potential of soybean aphid, it is an insecticide application that will significantly reduce aphid numbers and protect soybean yield during an outbreak, under non‐limiting nutrient conditions.