Impact of Hail Damage (Stand Thinning) On Irrigated Corn.

Proper implementation of hail insurance relies upon field evaluation techniques capable of accurately estimating losses across a wide range of timings throughout the growing season.

Currently, from V5 until the V9 stage, a hail stand reduction loss table is used to determine estimates of yield potential reduction for adjustment purposes. This table recognizes plasticity in yield plant^-1 as well as the interaction effects of final plant density. From V9 through milk stage, reductions in yield potential are assumed to be linear with stand reduction on a percentage basis. Research suggests that corn plants retain some level of yield plasticity past the V9 growth stage. Current methods of estimating yield reductions may not be appropriate for modern hybrids and management practices.

Field trials were established on the central High Plains near Garden City, KS in 2008, 2009, and 2011. and in the northern Great Plains near Prosper, ND in 2008-2010. Corn stands of 83,980 plants ha^-1 were established. Stands were reduced in a factorial of four rates (0, 25, 50, and 75%) and four timings (V5, V8, V11, and V14). In general, final grain yields were reduced as stand removal increased and timing was delayed. The impact of reduction rate increased as time of reduction was delayed. Stand reduction of 75% reduced grain yields 48, 54, 60, and 62% at V5, V8, V11, and V14 timings. Yield losses were underestimated by 3% at the V5 timing. Losses were overestimated on average 5.2, 38.3, and 30.3% for the V8, V11, and V14 timings. Overestimation errors increased with increasing levels of stand reduction. The relative importance of ears plant^-1, kernels ear^-1, and kernel weight yield components varied with timing of stand reduction. The results of this study suggest that adjustment procedures for late season stand reductions do not adequately reflect late season plasticity in corn grain yield components.