Plot size and shape in relation to soybean resistance for velvetbean caterpillar (Lepidoptera: Noctuidae)

During 1986, 1987 and 1988, selected plot sizes andshapes were evaluated for suitability in field experiments designed to compare soybean,Glycine max (L.) Merrill, cultivars for resistance to larvae of the velvetbean caterpillar, Anticarsia gemmatalis (Hubner). Plot size or shape did not significantly affect the relativerankings between cultivars in density or percentage of defoliation; therefore, any of the plotsizes or shapes examined in our experiments appear suitable for use in field experiments tocompare soybean cultivars for resistance to this defoliating pest. Plot size and shapeinfluenced the mean and precision of density and injury estimates. Estimates of larval density and percentage of defoliation were greater in plots of two or more rows than in one-row and hillplots. Precision of density and percentage of defoliation estimates were best for the plot sizeof two linear rows each 3 m long. Consequently, a plot size of two linear rows each 3 mlong appears the best option for field screening experiments