Effects of Ethephon on Morphology, Yield, and Lodging in Williams 82 Soybean

Lodging reduces yield in soybean [Glycine max (L.) Merr.j. Ethephon [(2-Chloroethyl) phosphonic acid] has been proposed as a harvest aid to improve soybean lodging resistance. The effects of ethephon rate and time of application on ‘Williams 82’ soybean grown at Urbana, IL, were investigated using a Drummer silty clay loam (fine-silty, mixed, mesic Typic Haplaquoll). Ethephon was applied at V3 and V7 stages of development at rates of 0, 0.13, 0.25, and 0.38 lb a.i./acre. Plants were divided into one upper and one lower portion to facilitate closer examination of plant morphology. Ethephon reduced stem length and leaf area, particularly in the lower plant. Upper stem elongation compensated for ethephon induced lower stem length reduction in the 1987 V3 treatments. Ethephon application increased lodging in 1987, a favorable year for soybean production. But in 1988, smaller, drought stressed plants did not lodge. Application at V3 significantly increased leaf abscission compared with the later application. Total nonstructural carbohydrate and starch in the three basal stem internodes declined with increasing ethephon rates for the V3 application, but increased for the V7 application. Free sugar levels in these basal nodes were unaffected by treatment. Midstem free sugar levels declined with increasing ethephon rate. Relative water contents in R5 lower stem segments were reduced by ethephon treatments relative to midstem segments in 1988. Ethephon treatment reduced leaf area more than plant height, especially in the lower plant. This may have reduced yield for all ethephon treatments and reduced lower stem carbohydrate status for V3 treatments. Ethephon also reduced pod number in the lower plant for V3 but not V7 applications. While ethephon application produced the desired stem morphological change, 1987 results indicate that other effects weakened the lower stem's resistance to bending.