Corn in Mississippi
When do corn borers reduce corn grain yield?
There may be some confusion regarding the potential for corn borers to reduce grain yield by damaging corn at various growth stages during which they infest corn.
Corn
borers, as their name indicates, tunnel into vegetative tissue causing
considerable vascular damage to the plant. All three corn borer generations
typically encountered during a season are capable of reducing corn grain
yield by causing physical stalk damage which can result in unharvestable
plants. This may be caused by killing the growing point during the whorl
stages (deadheart), stalk lodging, ear droppage, or stalk girdling.
However, the corn borers' tunneling activity also substantially damages the plants' ability to utilize energy and water necessary for physiological growth and development. This stresses kernel development causing physiological grain yield reduction. Corn is most sensitive to limited energy during early reproductive stages immediately following pollination. Therefore, mid-season infestations of second generation corn borers (which typically occur beginning during late June or early July) can result in severe physiological grain yield reduction. Most literature and Mississippi field samples indicate a grain yield reduction of about 8% per borer tunnel per plant. This yield reduction is unrecognizable by observation (hidden damage) and exclusive of the harvest loss described in the previous paragraph.
This physiological yield reduction may be avoided during third generation infestations if the corn reaches physiological maturity before vascular damage occurs. However, late maturing corn typical in northeast Mississippi may not reach physiological maturity before the third generation occurs, exposing these plants to moderate physiological yield loss and considerable stalk girdling which will result in lodging. Furthermore, if wet weather delays harvest, corn borers may also have ample time to girdle stalks, causing substantial lodging.