Effects of Induced Plant Resistance and Potassium Fertilization Rates on Soybean Looper (Chrysodeixis Includens) Development in Soybean

Soybean looper, Chrysodeixis includens (Walker), is one of the most destructive pests of soybean in the southern U.S. It is highly resistant to most insecticides. Induced host plant resistance and cultural control are sought as alternative control tactics. In this study, effects of induced resistance by exogenous application of elicitors were estimated on soybean looper development in soybean. Three different known elicitors of SAR (systemic acquired resistance), Actigard 50WG (acibenzolar-S-methyl), Regalia (extract of Reynoutria sachalinensis) and methyl jasmonate (MeJA), were applied to soybean plants at R2 and R5 stages to determine if these chemicals could induce plant resistance and lower soybean looper fitness in the field. All of the SAR elicitors had significantly adverse effects on soybean looper development time, defoliation, and pupal weight. In particular, applications of MeJA significantly reduced pupal weight by 6.8% and delayed larval development by 14.3% compared to untreated checks. The results suggest that exogenous elicitors can trigger plant resistance against herbivores and may have a place in integrated pest management. Inorganic fertilizers increase yield but sometimes also stimulate insect outbreaks. Potassium (K) fertilizer plays an important role in crop production. In this study, different rates of K fertilizer were used to detect their effects on soybean yield and soybean looper development. Soybean plants were supplied with six different rates of K (0, 33.6, 67.3, 100.9, 134.5, and 168.1 kg/ha as K2O) in field trials. Soybean leaves were sampled at R1, R3, R5, and R6 stages and fed to soybean looper in laboratory bioassays. Soybean looper consumed more tissues and spent less time completing larval development when fed on foliage from treatments of 134.5 and 168.1 kg/ha. Pupal weight significantly increased at 134.5 and 168.1 kg/ha. Soybean yield and 100 seed weight were also significantly enhanced at 168.1 kg/ha, but seed protein and oil content were not affected by K fertilization. Higher K fertilizer rates can enhance soybean yield but also improve soybean looper development. Therefore, K fertilizer rates will need to be balanced between increased yields and reduced herbivore populations