Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2005
Publication Date: 9/30/2005
Citation: Robinson, A.F., Akridge, R., Bradford, J.M., Cook, C.G., Gazaway, W.S., Kirkpatrick, T.L., Lawrence, L.W., Lee, G., Mcgawley, E.C., Overstreet, C., Padgett, B., Rodriguez-Kabana, R., Westphal, A., Young, L.D. 2005. Vertical distribution of Rotylenchulus reniformis in cotton fields. Journal of Nematology. 37(3):265-271. Interpretive Summary: There are many kinds of microscopic worms called nematodes that feed on the roots of cotton and other crops, debilitating the plants and markedly decreasing yields. The direct losses to U.S. cotton farmers caused by nematodes each year are estimated by the National Cotton Council to exceed $300,000,000. The reniform nematode is one of the most destructive to cotton production in the U.S. As a standard practice, agricultural consultants make nematode management recommendations to cotton farmers based on the nematodes found in the top foot of soil. Cotton roots usually grow much deeper than 12 inches, however, and we found in previous studies in south Texas that reniform nematodes feeding on these deep roots can reduce the yield potential of a cotton crop by 33%. To get a better idea how important an effect deep reniform nematodes might be having in other cotton production regions in the United States, we collected soil cores 4 feet deep from 20 carefully selected cotton fields in Texas, Louisiana, Arkansas, Mississippi, Alabama and Georgia, and analyzed the vertical distribution of nematodes, cotton roots and soil texture. We found that maximum nematode density below the top 12 inches at 19 out of 20 fields was greater than the standard threshold for nematode management. In fields with certain kinds of soil, the highest concentrations of nematodes in the soil were below the top foot even though most roots were above it. In these cases there likely is especially heavy damage to the deep roots that plants depend on as the soil dries down between rains and irrigations. This knowledge will be an important key to improving cotton crop management decisions where the reniform nematode is present.
Technical Abstract: The possible impact of Rotylenchulus reniformis below plow depth was evaluated by measuring the vertical distribution of R. reniformis and soil texture in 20 symptomatic fields on 17 farms across six states. The mean nematode population density per field, 0-122 cm deep, ranged from 0.4 to 63 nematodes/g soil and in 15 fields more than half of the R. reniformis present were below 30.5 cm, which is the greatest depth usually plowed by farmers or sampled by consultants. In 11 fields where measured, root density was greatest in the top 15 cm; however roots consistently penetrated 92-122 cm deep by midseason and in five fields in Texas and Louisiana the ratio of nematodes to roots increased greatly with depth. Repeated sampling during the year in Texas indicated that up to 20% of the nematodes in soil below 60 cm in the fall survived the winter. Differences between Baermann funnel and sugar flotation extraction methods were not important when compared with field-to-field differences in nematode populations and field-specific vertical distribution patterns. The results support the interpretation that R. reniformis below plow depth can significantly impact diagnosis and treatment of cotton fields infested with R. reniformis.