Location: Southern Insect Management Research Unit
Title: Impact of defoliation on yield of group IV soybeans in Mississippi Authors
Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 6, 2013
Publication Date: December 1, 2013
Citation: Owew, L., Catchot, A., Musser, F., Cook, D., Jackson, R.E., Allen, K.C. 2013. Impact of defoliation on yield of group IV soybeans in Mississippi. Crop Protection Journal. 54:206-212. Interpretive Summary: Numerous insect pests feed on soybean and potentially have an impact on the overall yield achieved in production fields in Mississippi. Depending on the nature of the insect in question, some cause damage by feeding directly on the developing pod and others by feeding on other plant parts, especially the developing leaves. The impact on yield of insect defoliators that feed directly on leaves of developing plants can vary depending on the growth stage of the soybean plant at the time that feeding occurs and the extent of the defoliation. Also, yield can be impacted by feeding on leaves in the upper versus lower portions of the plant canopy. Field experiments were conducted during 2009 and 2010 in two locations in Mississippi to evaluate the impact of insects feeding on soybean leaves during different growth stages and at different heights on plants by means of manual defoliation of test plants. There was greater yield loss from defoliation occurring in the upper plant canopy compared with the lower plant canopy during the earliest two plant growth stages that were examined. Once developing seeds had filled within the pods, no difference between plant canopy regions was observed. Results confirmed that yield loss was greater when soybean pods and seeds were in earlier stages of developing than when seeds were closer to maturity. However, yield losses were not significantly different between the earliest examined stages until defoliation exceeded 63% of the leaf area. The information gathered from this study was used to develop yield loss equations for the soybean growth stages examined. These can be used for making management decisions about the benefits of controlling defoliating insects based on the value of the crop and cost of control.
Technical Abstract: Field experiments were conducted during 2009 and 2010 to evaluate the effects of defoliation on maturity group IV soybeans, Glycine max (L.) Merr., grown in Mississippi. During each year, two locations were planted with maturity group IV soybeans that were subjected to various levels of defoliation during R3, R5, and R6 growth stages. Soybeans were subjected to various levels of defoliation within the upper 50% of the plant canopy, lower 50% of the plant canopy, and whole-plant canopy. There was greater yield loss from defoliation occurring in the upper plant canopy compared with the lower plant canopy during R3 and R5 stages, but no difference between canopy regions during R6 stage. Yield loss from whole plant defoliation was greater than upper or lower canopy defoliation. Results confirmed that soybeans during R3 and R5 stages are more susceptible to yield loss than during R6. However, yield losses were not significantly different between R3 and R5 until defoliation exceeded 63%. Dynamic economic injury levels were determined for each growth stage based on yield loss equations, value of the crop, and cost of control and can be used as a basis for developing action thresholds in high-yielding soybean production environments.