Dr. Pat Phipps, Virginia Tech, 6321 Holland Rd., Suffolk, VA 23437, Phone (757) 657-6450 ext. 120 or 143, FAX (757) 657-9333, email pmphipps@vt.edu
Significant Nematode Species: Five species pose an economic threat to Virginia cotton – southern root-knot, reniform, lance, lesion, and stubby root nematodes. All of these species, except reniform, are widely distributed throughout the cotton production area of Virginia, which consists of 10 counties/cities in the southeastern coastal plain of Virginia. Reniform nematode has currently been confirmed in causing significant damage to cotton only in Southampton County, Virginia. Diagnostic samples and field surveys in 2003-2004 have indicated an increase in problems caused by southern root-knot nematode in cotton. This increase appears to be linked with the reduction in peanut acreage and more continuous cropping of cotton. Currently, peanut is the only major crop in the region that is not a host of the nematode. Soybean and corn are major crops in the region that are hosts of southern root-knot.
2004 Estimate of Yield Loss to Nematodes: 3.7% of cotton yield was lost to nematode damage ... 5736 bales ... valued at $1,992.025 assuming a value of $0.72/lb, based on results of on-farm tests, diagnostic samples, and soil surveys.
2003-2004 Research Activities: Field testing is focusing on defining the susceptibility of commercial cotton varieties to southern root-knot nematode, and evaluations of chemical control. Significant differences have been detected in variety susceptibility to southern root-knot nematode over the past four years. Varieties showing significantly less root damage in 2004 included DP434RR, SG215BG/RR, DP444BG/RR, ST5599BR, and ST5242BR. Variety selection and Temik 15G increased yield significantly, and the use of Temik 15G at 5 lb/A in-furrow increased yield an average of 0.17 bales/A ($59/A). Evaluations of chemicals in field trials have included experimental compounds, Temik 15G in-furrow and banded over rows, soil fumigation with metam sodium, and seed treatments with abamectin and other chemicals. Temik 15G at 5 lb/A in-furrow continues to be the most widely used treatment for control of nematodes in Virginia.
2005 Activities for Cotton Producers to Consider: The practices of growing cotton continuously, reduced tillage, and planting in stale seed beds poses the highest risk for developing severe nematode infestations. The rotation of peanut with cotton helps curb the buildup of southern root-knot and reniform nematode in fields. Effective nematode control requires a combination of practices which include crop rotation, tillage to reduce overwintering of nematodes infested roots, variety selection, and chemical controls.