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Be vigilant in monitoring late-planted corn

Agriculture.com Staff 05/30/2007 @ 12:45pm

Thanks to an Easter freeze and May's unusually heavy rains and flooding, some corn in Kansas and other areas was planted or even re-planted late this year.

"That does not necessarily mean we won't have a good corn crop," said Kansas State University plant pathologist Doug Jardine. "It does mean that growers should be especially watchful for such problems as cold weather crown stress, crazy top downy mildew, gray leaf spot and southern rust."

Some corn plants could develop signs of cold weather crown stress over the next few weeks, said Jardine, who is the state leader for K-State Research and Extension plant pathology. Corn that has been struggling to grow in waterlogged soils can be prime candidates for this problem because their roots may have been deprived of oxygen.

Plants that have developed cold weather crown stress may appear stunted. They can have symptoms of potash, phosphorus or zinc deficiency, even if there are enough of those elements in the soil. When split open, the plants will have crowns that are dark brown or black.

Such plants can still yield a crop, he said, but will be more susceptible to drought stress and stalk rot later in the growing season.

In corn that was waterlogged shortly after emergence, another problem to watch for is crazy top downy mildew, Jardine said. Evidence of that disease may not be apparent until the tasseling stage, when affected plants will grow a leafy structure (crazy top) rather than tassel out.

"Crazy top results in sterile plants," Jardine said. "Even if just 5 percent of a farmer's corn has crazy top, that's a 5 percent yield loss."

Gray leaf spot and southern rust may be more of a factor in Kansas this year than usual, the scientist said.

"Typically, corn in Kansas is far enough along in its development when these two diseases appear that economic yield loss does not occur. With corn lagging behind because of the delayed planting, however, these diseases may affect the corn earlier in its development this year, causing more significant yield reductions."

Again, the best way to assess the risks is to walk the fields, Jardine said. If gray leaf spot and southern rust are detected early enough and in enough of the crop, a fungicide application may be in order.

Thanks to an Easter freeze and May's unusually heavy rains and flooding, some corn in Kansas and other areas was planted or even re-planted late this year.

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