Defoliation Responses of Determinate and Indeterminate Late‐Planted Soybeans1

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Abstract
Late‐planting (later than 15 June) in double‐cropping systems is a common practice among soybean [Glycine max L. (Merr.)] growers in the southeastern USA. Many experiments have been conducted to evaluate the effects of insect or hail‐simulated defoliation on yield and agronomic characteristics of full‐season soybeans, but information on defoliation response of late‐planted soybeans is lacking. Field experiments were conducted to determine effects of complete defoliation of late‐planted soybeans at stages of development R4, R5, and R6. Yield and yield components of determinate cultivars ‘Braxton’ and ‘Foster’ were compared to those of indeterminate ‘Duocrop’. Defoliated plants generally matured earlier, lodged less, and had smaller seeds and fewer pods per plant than undefoliated controls. Defoliation had no effect on plant height except in Duocrop, which was shorter when defoliated at the R4 stage. Average yield losses for the determinate cultivars were 72, 81, and 40% and 67, 87, and 44% for the indeterminate cultivar following defoliation at the R4, R5, and R6 stages, respectively. Yield loss was primarily attributed to a reduction in number of pods per plant. Indeterminate Duocrop had no advantage over determinate Braxton and Foster for defoliation recovery when planted late.

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