Dr. Charles Overstreet, Extension Nematologist, Louisiana Cooperative Extension Service, Louisiana State University, P.O. Box 25100, Baton Rouge, LA 70894-5100, Phone (504) 388-2186, FAX (504) 388-2478
Major Nematode Species: Reniform and root-knot nematodes continue to cause major damage to Louisiana cotton. Reniform nematodes are the most important parasitic pest in the state. Lance nematodes also account for serious damage each year, but they have not yet caused loss levels as high as those attributed to reniform nematodes.
A survey of 21 parishes in 1998, shows shifts in distributions and densities of reniform nematodes (in silty loam soil) with increased populations in two parishes and decreased populations in three. Root-knot nematodes (in sandy soil) remained relatively stable with population densities increasing in three parishes and decreasing in three parishes. It was observed that where reniform nematodes invade areas infested with root-knot nematodes ... reniform nematodes tend to be dominant.
Population densities of lance nematodes increased in two parishes and decreased in seven parishes.
Other Nematode Species: Surveys in 1994-1995 reported the following nematode species: lance, spiral-H, spiral-S, lesion, stunt, stubby root, pin, cyst, dagger, and ring. Populations of most of these species were below threshold levels.
1998 Yield Loss Estimate Valued at $390/Bale: 7.0% of the cotton crop was lost to nematode damage ... 54,819 bales ... valued at $21,379,410.
Seven-year Average Yield Loss Estimate from 1992 through 1998: Annual average of 5.86% of the crop was lost to nematode damage ... 78,426 bales ... valued at $29,698,254.
1999 Activities to Consider in Latter Part of Growing Season: University specialists say the reniform nematode population peaks in July. Soil sampling should begin that month and continue through December. Reniform nematode damage is an economic threat growers can fight effectively. State researchers and advisors strongly recommend nematode management programs that integrate cultural practices and chemical controls to reduce nematode populations below damaging levels. Survey information on the distribution of nematodes does not support grower complacency, or a wait-and-see attitude. Cultivars and crop rotation are among the cultural practices some growers use successfully. For short term control, nematicides applied in early season proved protection for plants allowing them to develop healthy root systems.
1998 Research Activity: Four trials were conducted to determine the effects of nematicides; and several tests were done with cotton varieties to determine levels of resistance to reniform nematodes.
For details of test results, contact Jennifer Gimpert.