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Thursday, Jan. 19, 2017

Hot, dry weather always a concern

Posted Tuesday, August 9, 2011, at 9:57 AM

The heat and dry weather is a concern for crop producers. Crops are now on the defensive. This can be seen in the rolling of corn leaves and flipping of soybean leaves. Crops south of I-70 seem to be more severely affected than crops north of I-70. As you go further south from I-70 there are patches in both corn and soybean fields where plants are dead as well as fields in general suffering from severe drought stress.

What can be controlled to reduce stress on the crop? Insects are still active with the heat favoring the development of grasshoppers and spider mites. Reports of grasshopper damage to soybean have been received. Dry weather and dry-down of grasses in field borders and waterways will force grasshoppers into growing field crops. Grasshopper numbers often occur on a 4-5 year cycle and this looks like a peak year for grasshoppers in most areas of Missouri. Treatment is justified in corn when 7 or more grasshoppers per square yard are present and foliage is being severely damaged. After pollen shed, control may be necessary if grasshoppers are damaging foliage above the ear zone. Treatment is justified on soybeans when defoliation reaches 30% before bloom, 20% bloom to pod fill, or when 5 to% of pods are damaged and hoppers are present. In grass pastures, treatment is justified when grasshopper numbers reach or exceed 7 grasshoppers per square yard. The smaller the grasshoppers are when treated the better chance of control.

Spider mites thrive under dry hot conditions, so keep monitoring for them. Look for damage first along edges of fields as they tend to move in from grass areas.

Normally by this time of year, we are looking for late season soybean diseases to show up. At this point, we are not seeing a lot of foliar diseases developing. The hot, dry weather does not favor the development of leaf diseases. Plants dying from stress compounded by root systems damaged by Phytophthora, Rhizoctonia or Fusarium root rot may be more common. If soybean cyst nematodes (SCN) are present in soybean fields, this may be adding to the stress on soybean plants. This would be a good year to sample for SCN. The prolonged period of hot, dry weather may result in reduced sudden death syndrome symptoms this year. In areas in which drought has been severe, charcoal rot may be damaging or killing soybean plants. Also, the current threat of soybean rust in Missouri is extremely low.

If you have any alfalfa, the potato leaf hopper has been reported and may cause damage to alfalfa plants. Heavily damaged plants may die, especially seedling alfalfa.

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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.
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