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Thursday, July 31, 2014
Recent cold snap ideal for corn diseasesPosted Monday, June 6, 2011, at 4:41 PM
Recent growing conditions, such as cold weather, temperature fluctuations, excess moisture and saturated soil conditions have stressed the plants as well as provide near ideal conditions for disease development.
There are several leaf spot and leaf blight diseases that can develop on young corn plants. The following summary of symptoms can help distinguish between the more common diseases.
1. Anthracnose leaf spot usually occurs early in the season on the lower leaves of young corn plants. Anthracnose lesions tend to be brown, oval to spindle-shaped lesions with yellow to pinkish to reddish-brown borders.
Lesions may range from 0.2 to o.6 inch in length. Lesions may merge or coalesce to kill larger areas of leaf tissue. Lesions may be concentrated towards the leaf tip. Generally the disease stops as drier, warmer weather develops and is not considered a significant problem. Under conditions favorable for the disease later in the season, anthracnose may actually move up to the ear leaf and can also cause top dieback and stalk rot later in the season. High temperatures and extended periods of wet weather favor anthracnose.
2. Holcus leaf spot lesions are usually oval to elliptical and range in size from 0.25 to 1.0 inch. Initially they are dark green and watersoaked. Later they become dry and turn light brown with a reddish margin. Holcus leaf spot is caused by bacteria and is spread by wind-driven rain or splashing rain, so outbreaks frequently occur several days after a rainstorm or storm with strong driven rains.
3. Stewart's bacteria wilt symptoms on young corn plants will include linear, pale green to yellow streaks that tend to follow the veins of leaves and originate from feeding marks of the corn flee beetle. Lesions may extend to length of the leaf. Plants may appear stunted or somewhat distorted. With the more recent warm weather, corn in many parts of the state has really taken off, so symptoms of Stewart's bacterial wilt are beginning to develop on these rapidly growing plants. Most field corn hybrids have enough resistance to Stewart's bacterial wilt that additional management is not necessary.
4. Crazy top of corn is caused by the downy mildew fungus when young plants are subjected to saturated soil conditions or water accumulating in whorls or leaf sheaths. The disease causes a deformation of plant tissues including excessive tillering, rolling of leaves, and proliferation of the tassel until it resembles a mass of leafy structures and stunting of corn plants. The disease is seldom severe enough to cause significant losses.
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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.