Heads Up! Pest Alerts

Several cases of lower stalk lodging have been seen in corn in the Green River Area. The worst field is 90% lodged, with a number of fields showing areas with over 50% lodging. Corn producers are advised to check the lodging potential of their fields. A simple way to do this is to walk through the field and, keeping your hands at chest height, push stalks 8-10 inches from vertical. If 10-15% of the stalks lodge, schedule the field for early harvest before a strong wind results in severe lodging.

The following is a preliminary summary of our findings from the fields we visited. Producers should understand that lab analyses of the samples collected are still pending. There was a general pattern of stalk weakening in the fields examined. The majority of the stalks in all fields examined were weakened by factors other than insect damage. Evidence of stalk rot diseases was present, yet that evidence did not appear to be very consistent in the field inspections.

In a white corn field examined, severe pith deterioration along much of the stalk length and moderate to severe root rot. Several infectious stalk rots may have been present, including anthracnose, Fusarium stalk rot, and Gibberella stalk rot. However, I suspect physiological stalk weakening is the primary factor here, given the severity of the pith and root deterioration and the lack of consistent symptomatology of infectious stalk rots in the field. Lab analyses are pending.

In several fields of yellow corn, no more than approximately 15-20% of plants were weakened by southwestern corn borer. Most plants that had lodged had broken in places where the stalk exhibited localized areas several inches in length with slightly moderately deteriorated pith, with relatively little discoloration and no evidence of insect feeding. These may be sites of Fusarium stalk rot, physiological stalk rot, or Gibberella stalk rot (lab work pending).

It is unclear at this time whether the majority of the stalks were weakened from physiological stress or from infectious stalk rots. However, since physiological stalk weakening can often predispose plants to infectious stalk rots, all cases of lodging ought to be evaluated for stress factors, regardless of whether infectious stalk rots are found in our analyses.

The weather conditions reported this growing season set the stage for stalk weakening. Conditions favorable for high yields create a large ear that requires large amount of photosynthate. The overly cloudy weather during grain fill provides for reduced photosynthesis, so a high-yielding corn plant will draw reserves from the stalk, leading to stalk weakening. Factors that might then enhance this problem further include: excessive plant population, excessive N in relation to potash, high N levels early in the season followed by N loss through leaching or denitrification, inadequate levels of potash, low stalk strength ratings of hybrids planted, and severe leaf disease. Producers should evaluate these factors to see if there are ways to reduce the risk of lodging in future years.

Paul Vincelli
Dept. of Plant Pathology
University of Kentucky

	Original document: 1 September 2000 Last updated: 1 September 2000