Late Spring Frost and Postfrost Clipping Effect on Corn Growth and Yield

Lack of knowledge regarding early-season frost-damage effects on corn (Zea mays L.) restricts the ability of producers to make decisions regarding replanting and yield expectations. Our first objective was to monitor corn growth and yield within fields with a range of late-spring frost injury. The second objective was to evaluate post-frost clipping effects on plant growth and yield. Several days after a severe 21 June 1992 frost, plots were established at several Wisconsin sites in which within-field frost-damage to corn with 9 to 12 emerged leaves ranged from major (65 to 100% of leaves damaged) to minor (less than 5% of leaves damaged). Damage within fields varied primarily due to slight topography differences, with greatest damage in low-lying areas. Although nearly all plants recovered from the injury, plants with greatest damage were delayed in silking (7 to 10 d later), had reduced final plant (16 to 25 in. shorter) and ear (12 to 20 in. shorter) height and lower grain yield (42 to 59% lower) compared with plants with least damage. Postfrost clipping reduced grain yield by 15 to 34% at three sites, resulted in no differences at two sites, and increased yield about 10% at one site. Based on these results and previous studies, there is little consistent benefit to clipping frost-damaged corn. Research QuestionOn 21 June 1992 widespread frost-damage to corn occurred throughout the midwestern USA. Lack of documented knowledge regarding frost damage effects on corn regrowth restricted the ability of producers and advisors to make confident decisions regarding replanting and yield expectations after the injury occurred. Therefore, our first objective was to monitor corn growth and yield within fields with a range of injury. Following this frost, there was substantial debate regarding whether or not to clip plants in frost-damaged fields, to remove dead or deformed tissue above the growing point of plants. Our second objective was to evaluate clipping effects on plant growth and yield in growers' fields, in which field equipment was used to clip damaged corn. Literature SummaryField simulation of frost-damage to plants is difficult, therefore, frost injury yield effects are usually estimated using defoliation studies. But regrowth for plants in which both internal and external tissues have frost damage is probably different than for plants with primarily external leaf removal. A Wisconsin study observed corn regrowth and yield differences following a 23 June 1972 frost in a bowl-shaped field with a range in front damage. Nondamaged plants on highest land yielded 30% more and were advanced in maturity compared with damaged plants at the base of a slight slope. In previous studies, we found inconsistent results with post-frost clipping. Yields were increased by 40%, decreased by 30%, or not affected by clipping in different situations. These studies were conducted in small plots and clipped using scissors, rather than using field equipment practical for use by growers. Study DescriptionFrost-damage Several days after the 21 June 1992 frost, plots were established at five Wisconsin sites in which frost damage to corn with nine to 12 emerged leaves (four to seven emerged collars) ranged from major (65 to 100% of leaves damaged) to minor (less than 5% of leaves damaged) within individual fields. Damage varied within fields primarily due to slight topography differences, with greatest damage in low-lying areas. Clipping Clipping vs. not clipping within 3 to 5 d after the frost was compared within uniformly major-damaged fields at six sites. Growers performed clipping at heights of 4 to 12 in. using flail stalk choppers at five sites and a rotary lawn mower at one site. Applied QuestionHow did frost-damage influence corn regrowth and yield? Although nearly all plants recovered from the injury, plants with greatest damage were delayed in silking by 7 to 10 d and had reduced plant (16 to 25 in. shorter) and ear (12 to 20 in. shorter) height than those with least damage. Grain yields were reduced by frost-damage, with the extent of yield loss related to the percentage of exposed leaves which were damaged (Fig. 1). Yield losses from frost may have been particularly large in 1992, because the remaining growing season after the frost was extremely cool. But frost-damage in 1992 reduced yield to similar levels as in 1972, a warmer season that was more favorable for corn production (Fig. 1). Was there any benefit to clipping frost-damaged corn? Clipping reduced grain yield by 15 to 34% at three sites, resulted in no differences at two sites, and increased yield about 10% at one site. Based on these results and other studies, there is little consistent benefit to clipping frost-damaged corn. Fig. 1Relationship between percentage frost-damaged leaves (partially or fully-emerged) and percentage grain yield loss for corn grown in Wisconsin at five sites in 1992 and one site in 1972. Loss is expressed as frost-damaged yield as a percentage of minor-damaged (less than 5% leaves damaged) yield within sites.