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Vol. 17, No. 10
Article 8 of 10
May 25, 2007
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Scientists Find Crop-Threatening Levels of Root-Knot Nematodes in Southeast Missouri and Northeast Arkansas Cotton Fields By Allen Wrather Crop-threatening levels of root-knot nematodes (RKN) are present in some cotton fields in southeast Missouri and northeast Arkansas. During a recent survey, University of Missouri scientists found root-knot nematodes in 20 percent of the New Madrid County cotton fields, 27 percent of Pemiscot County cotton fields, and 43 percent of Dunklin County cotton fields. Reniform nematodes were very rare in Missouri. University of Arkansas scientists found root-knot nematodes in 70 percent of samples from Clay County, 32 percent of samples from Craighead County, 45 percent of samples from Green County, and 56 percent of samples from Mississippi County. Reniform was only in a few Mississippi County samples. Root-knot nematodes can cause severe injury to cotton. The symptoms of RKN injury will initially be visible 6-8 weeks after cotton emergence. The symptoms of root-knot nematode injury are stunted cotton plants, and these plants may wilt more quickly than healthy plants during a hot afternoon. Plants injured by these nematodes will also have swollen areas, galls, visible on infected roots. Be cautious about diagnosing the cause of stunted cotton because other factors such as low soil pH and drought may cause plants to be stunted. Ask your scout to tell you about areas in your fields where they observe this symptom and then determine the cause of the stunting. Growers suspicious of RKN problems in their cotton should dig up roots of stunted plants 6-8 weeks after emergence or soon after harvest and look for galls on the roots. Some but not all research results from southern states show that a side dress application of Temik and/or foliar application of Vydate from the first to seventh true leaf stage of growth will result in a cotton yield increase in fields with RKN. We do not have results from research in Missouri to support this. Cotton farmers can take precautions to avoid this problem next year. They should consider using a nematicide next year such as Avicta Complete Pak, Temik, or Telone in fields where RKN reduced yield. There are advantages and disadvantages to the use of each of these products. No cotton varieties are resistant to RKN, but Stoneville 5599 is tolerant. These nematodes will reduce yield of 5599 but not as much as they reduce yield of other varieties. Following these suggested procedures will give cotton farmers a better chance of producing higher yields and greater profits. For more information contact Allen Wrather at the University of Missouri Delta Center or check the Delta Center Web Page (aes.missouri.edu/delta).
Allen Wrather, Professor |
