Dr. Melvin Newman, Entomology and Plant Pathology Department, University of Tennessee, 605 Airways Boulevard, Jackson, TN 38301, Phone (901) 425-4718, FAX (901) 425-4720.
Major Nematode Species: Four species inflict observable damage to Tennessee cotton: reniform, spiral, lance and stunt nematodes. A reniform nematode alert is now in effect in the heart of the main cotton growing area in West Tennessee. The alert is based on extensive nematode soil sampling surveys started in 1997. Some of the counties involved include Crockett, Madison, and Gibson. In 1997 and 1998, soil samples from more than 80 fields in this area showed a growing population of reniform nematodes. There were 1,580 samples taken in 10 to 20-acre fields, representing 7% of the 450,000 acres of cotton grown in the state in 1997. Reniform nematodes were detected in 70 samples in Crockett, Gibson, and Madison counties. Nematode counts ranged from 1 to 268 per 200 cc of soil tested. (In 1996, reniform nematodes were found in only one field in this area). When diagnostic tests are completed on these samples, the distribution and density patterns of this pest can be better defined. Pending further survey results, the reniform nematode infestation in these three counties should be considered at a low density.
In 1998, 445,000 bales of cotton were harvested in 27 counties. Three counties -- Haywood, Crockett, and Tipton -- accounted for about 50% of the state's production. An additional 30% of the state's production came from four other counties -- Fayette, Lauderdale, Gibson, and Madison.
Other Nematode Species: Five other species that are found at below threshold population levels include: lesion, dagger, ring, cyst, and root-knot nematodes. Although root-knot nematode has been present in Tennessee for many years, it is the cause for least concern to the state's cotton growers.
1998 Yield Loss Estimate Valued at $390/Bale: 0.4% of the cotton crop was lost to nematode damage ... 2,512 bales ... valued at $979,680.
Seven-year Average Yield Loss from 1992 through 1998: Annual average of 0.23% of the crop was lost to nematode damage ... 1,778 bales ... valued at $675,724.
1999 Activities to Consider in Latter Part of Growing Season: If growers have not yet sampled their fields for nematodes, they are urged to do so as soon as possible. The best time to sample is soon after harvest. To sample a field, we recommend taking one probe for every acre. All samples from a field should be mixed well. Then a quart of soil should be taken from the mix ... placed in a plastic bag ... and shipped to the diagnostic center for analysis. Samples should be submitted to:
Tennessee Plant Pest Diagnostic Center, 5201 Merchant Drive, Nashville, TN 37211-5201, ATTN: T. S. Stebbins, Laboratory Diagnostician, phone (615) 832-6802. Call for analysis cost.
General guidelines for judging minimum threshold population levels for reniform nematodes are: Preplant Count -- 1,000 juveniles per pint of soil; Harvest Count -- 5,000 juveniles and adults per pint of soil.
Growers who know they have nematode problems should start immediately with a good nematode management program that incorporates both cultural and chemical controls for nematode suppression. Recommended cultural controls include crop rotation with grain sorghum and/or corn. There may be some soybean varieties that will also give good results. The most effective chemical control for Tennessee growers is Temik 15G applied in-furrow at planting time. Test results show that Temik provides protection for plants during the early growing season, which allows plants to develop healthy root systems.
1998 Research Activities: A test was conducted in 1998, in Madison county, to determine the effectiveness of Temik 15G on the suppression of reniform nematodes.
For details of test results, contact Jennifer Gimpert.