U.S.A. Midwest farmers are seeing more stalk rot this year than most years. Weather during the growing season is the most likely the cause. Early season moisture established good growing for much of the corn growing areas. Rain was more than average for many areas, although others were excessively dry. Most of the summer was warmer than normal as well. Plants responded to the heat by moving to flowering quicker than in some summers. Extra water resulted in more shallow roots but also good extension of the silks and high kernel numbers. Weather after flowering also varied with warmer than normal temperatures, high humidity and scattered rain showers in much of the upper Midwest.
Humid warm nights favored the fungi causing gray leaf spot and tar spot. Areas with frequent rain during the month after flowering developed significant northern leaf blight on corn. Each of these diseases destroyed significant photosynthetic tissue in susceptible corn hybrids. Weather during that period also tended to be cloudy, reducing the rate of photosynthesis. Warm nights increased the cellular respiration rate more than the cool Midwestern nights that are more common in these areas. 2018 summer weather in much of the US corn belt resulted in high kernel numbers, photosynthetic stress after flowering due to leaf disease and cloudy weather. Competition for use of reduced levels of sugar between translocation to the kernels, and cytoplasmic respiration in all plant tissues frequently resulted in degradation of roots and eventual root rot. This was followed by plants wilting. Many fungal species invaded the dying stalk tissue created the obvious symptoms of Fusarium, Gibberella, Diplodia or Anthracnose stalk rots.
Hybrids that showed a high incidence of stalk rot in 2018 probably would have been OK if this specific weather pattern had not occurred. Correctly predicting the 2019 weather will be helpful in deciding on the best hybrid, tillage, plant density and other inputs for that season. This is not an easy task.
Visit us at the ASTA in Chicago, Dec 9-12 (booth G207)
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.