Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
We have seen a few processing sweet corn varieties in our variety trials that are showing leaf scald symptoms in the upper canopy (see photos below). Most of the varieties in the trial had little or no leaf scald.
This type of leaf scald is a physiological disorder and is not caused by a disease pathogen. Newly emerged leaves in the upper canopy of susceptible varieties that are the most exposed will be the most likely to scald.
Leaf scald occurs most commonly when temperatures are in the high 90s. At these air temperatures, crop leaf temperatures may rise to a critical level where plant cells are damaged and they desiccate quickly, leaving the scalded appearance. Upper leaves are the most exposed to radiation from the sun and therefore the most susceptible. Drying winds and low humidity will make scald more severe. Any interruption in transpiration during this period will increase leaf temperature even more and make scald more severe.
Three rows of a variety showing scald flanked by unaffected varieties.
Variety on the right affected by scald, variety on the left unaffected.
Close up of scalded leaves.
Scald is a very rapid tissue death. Leaf scorching, especially on margins, is more common and related to water stress, soil moisture deficits, or root system problems where inadequate water cannot be taken up. This is often most prevalent on larger leaves. Leaf tissues that are furthest from the veins (the margins and areas between the veins) are the first ones affected by the lack of water, leading to this scorch.
Leaf scald and scorch can also be cause by disease organisms in some vegetables. Most commonly we see this with bacterial and fungal disease organisms that affect vascular systems of plants. Verticillium wilt would be a good example. In Nebraska, Colorado, and some Midwestern states, Goss’s wilt in corn causes upper canopy leaf scorching. This is a bacterial disease that is not present in the East. However, Stewart’s wilt is common in our area in susceptible sweet corn varieties and will cause scorch-like symptoms. Use of resistant varieties is the best control for vascular diseases that cause scorch.