Weekly in-season Updates
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INFORMATION |
October 2, 2006 Talkin’ Cotton J.C. Banks
We have been observing several fields in Oklahoma that show symptoms of a condition known as premature senescence syndrome. Leaves in the top of affected plants first show a yellowing between leaf veins, which quickly changes to a yellowing and bronzing of leaves throughout the plant followed by defoliation of the leaves. This condition was described by Dr. Robert Lemon and Dr. Mark McFarland of Texas A&M University in 2003 on cotton in South Texas that had been through an extended drought period and received late season rainfall. It is triggered by a deficiency of potassium in the plant, which allows the pathogens Alternaria and Cercospora to attack the weakened plant. Cotton plants that have a good boll load have a high requirement for potassium to support fiber development. Normally the root system is large enough to mine potassium from the soil, but any condition that limits root growth will limit potassium uptake. This can be a lack of soil moisture, or even a perched water area in irrigated soils that limits root growth to the top few inches of the soil profile. Under these conditions, the plant cannot take in enough potassium to support the needs of developing bolls. The Alternaria and Cercospora are secondary leaf pathogens, and they attack the weak plants and cause defoliation. Normally the cotton is near the end of boll development and even though the field looks bad, there will not be a large effect on yield, although micronaire might be lowered. There will be some plants in the field that are taller and are not affected as much as others, but usually upon examination, these plants are not supporting a heavy boll load. There is no chemical treatment that will be effective on this syndrome, but affected fields should have a boll opener and a desiccant applied if needed, and harvested when the plants are dried down and bolls are open.
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