Severe Defoliation of Vegetative Maize Plants Does Not Reduce Grain Yield: Further Implications with Action Thresholds

It is commonly perceived that early defoliation of maize (Zea mays L.) is a significant risk for maximum grain yields. However, several studies designed to assess biotic and abiotic factors that reduce leaf area reported contrasting results. When maize suffers defoliation before developing its seventh leaf (V7 stage), plants can often compensate without impacting grain production. Seventy-five percent of 20 reviewed publications that offer empirical information indicated severe defoliation did not affect maize yield when plants were less than V7. We present field results for six maize hybrids, lines, and a landrace with severe (75%) defoliation one, two, or three times before reaching V7, in Maryland. Results showed that despite multiple, severe defoliation, there were no significant differences in grain yield (P > 0.05). Despite seven amounts of defoliation, yields for each defoliation amount did not differ from yields for intact plants. One early defoliation at V2 significantly produced more grain than did the nondefoliated check (P < 0.05). Results confirm the ability of maize to compensate or over-compensate for vegetative-stage defoliation. Results are also discussed in relation to recent reviews of previous studies. It is imperative to reconsider unnecessary recommendations to apply insecticide against maize defoliators when maize plants have yet to develop the seventh leaf.