Stalk rot in Corn
As corn matures and seed fill progresses, the plant will mobilize or move sugars from the stalk and leaves to fill the kernels. This process is referred to as stalk cannibalization and causes disintegration of the pith cells. This process in turn results in weakened stalks which are susceptible to physiological stalk lodging and stalk rots. Stalk rots, depending on the season, can lead to a 5 to 20 percent loss of yield potential. Stalk rot tends to involve more than one causal organism. Stalk rots are favored by good growing conditions early in the season, followed by stress after pollination. Stresses can include a lack of moisture, nitrogen deficiency, foliar disease, hail damage and prolonged cool cloudy weather conditions. Extended periods of dry or wet weather prior to pollination, followed by abrupt changes for several weeks after silking, favor the development of most stalk rots. Fields need to be scouted for signs of stalk rot and harvest targeted for fields where stalk rots are developing.
Common stalk rots to watch for:
Anthracnose Stalk Rot: Symptoms usually occur just before the plant matures. A shiny black discoloration develops late in the season as blotches or streaks on the stalk surface, especially on lower internodes. Internal stalk tissue may become dark and soft, extending several internodes. Often the entire plant is killed and several internodes are rotted. Lodging typically occurs higher on the stalk than other rots.
Diplodia stalk rot: With diplodia stalk rot, the lower intern odes become straw-brown, spongy and dry. The pith tissues disintegrate, leaving vascular strands intact.
Fusarium stalk rot: Stalks prematurely turn brown and are susceptible to breakage. When stalks are split, a whitish-pink to salmon discoloration may be visible.
Gibberella stalk rot: Affected plants may wilt with leaves turning a dull gray-green. The lower stalk softens and becomes straw colored as plants die. The inside of a rotted stalk has a pink to red discoloration.
As the harvest season progresses or especially if it is delayed due to weather conditions, fields should be scouted for symptoms of stalk rot. Different fields, different hybrids and different management practices should be evaluated separately. There are two methods to evaluate for potential stalk rot problems. The squeeze test involves squeezing or pinching each stalk a couple of nodes above ground level. Healthy stalks are firm and cannot be compressed. If over 10 to 15 percent of the stalks are rotted, significant lodging is possible. The second method is a push test. Select 10 plants in a row and push each stalk 45 degrees from upright. If more than 10 to 15 percent of stalks lodge or feel spongy, then the field should be harvested earlier.