Corn foliage diseases showing up
This is shaping up to be another “interesting” year for corn and other field crops in Missouri and most of the Midwest. Prolonged periods of wet weather and then flooding delayed planting or led to replanting. Overall the corn crop is behind normal although not as far behind normal as it was at this time last year. There is also a wide range in growth stages of corn across the state. We have not received many samples or calls related to corn foliage diseases but with the most recent bout of wet weather, it is likely that corn foliage diseases may begin to show up in fields.
So far the samples that have been submitted have had anthracnose leaf blight on the lowest leaves, especially in fields with corn on corn (see May 24 issue of the Integrated Pest & Crop Management Newsletter for more detailed information on anthracnose of corn). However, corn growth over the last week to 10 days has been incredible. Plants that were at the 2-3 leaf stage around June 5 are now 3-4 feet tall. The anthracnose lesions which were so evident on the first true leaf and the oldest, smallest leaves on plants in early June are in some cases now hard to find. The small leaves at the very base of the plant have sloughed off or are sloughing off and lesions are not very prevalent on the leaves that have emerged with the rapid growth over the last week to 10 days.
Gray leaf spot, common rust and southern rust are the foliage diseases most likely to occur on corn in Missouri over the next few weeks. Northern corn leaf blight does not occur every year but may occur in wet or cool, wet years so that would be another foliage disease to look for when scouting fields. I have had some questions about the bacterial leaf spot, Holcus leaf spot. Although this disease would be likely to occur after hail storms or rain storms with hard, driving winds, I have not seen any samples that were positive for Holcus leaf spot yet this year.
Generally speaking with the corn foliage diseases, the later in the season (especially the longer after pollination) that the foliage disease becomes established, the lower direct yield losses will be. Highest yield losses occur if diseases such as rust or gray leaf spot develop prior to pollination. Also, most of the corn foliage diseases are favored by extended periods of free moisture on the leaf surfaces. This moisture can be from rain, overhead irrigation or heavy dews that stay late in the day. Fields with poor air movement, river bottom fields or shaded portions of fields may also have higher levels of corn foliage diseases.
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