Nematodes damage plant roots by puncturing root cells to feed on plant nutrients. This damage reduces the availability of moisture and nutrients to the plant, resulting in wilted, stunted, and yellowing plants (Figure 1).1
Plants damaged by root-knot nematode are often grouped in patches of the field with no pattern. Reniform nematode usually occurs throughout the field but may not cause damage in every area that it is present.2
Fields planted in cotton year after year may have a higher incidence of nematode damage. Rotating to a non-host is recommended, but knowing the nematode species is paramount when selecting a rotation.3
Nematode damage to cotton costs producers millions of dollars per year, but lower yields are often directed toward wet or dry areas of the field, or fertility, insect and disease problems.2
Although nematodes can be found across soil types, damage is more likely to be found in coarser textured soils like sandy loams.3 Southern root-knot nematodes in clayey soils with a higher water holding capacity have been observed to have lower egg hatch and motility, reducing potential damage.4
Nematode damage late in the season can lead to premature death, defoliation and maturity (Figure 2).2
Root-knot nematode causes galling of the roots, which can be observed when an infected plant is carefully removed from the soil (Figure 3).2
Root-knot nematode damage greatly increases the incidence of Fusarium wilt. It is likely that root-knot nematodes are present if plants are infected with Fusarium.1
Soil sampling should be conducted to confirm the presence of nematodes and identify the species. For more information about how to soil sample, refer to 6004_Q1: How to Sample Soil for Nematodes.
1 Overstreet, C. and Xavier-Mis, D. 2016. Nematode problems on cotton. Louisiana State University. https://www.lsuagcenter.com/profiles/coverstreet/articles/page1460046020798.
2 Understanding cotton nematodes. National Cotton Council of America. https://www.cotton.org/tech/pest/nematode/ucn.cfm.
3 Mueller, J., Kirkpatrick, T., Overstreet, C., Koenning, S., Kemerait, B., and Nichols, B. 2012. Managing nematodes in cotton-based cropping systems. Cotton Incorporated. https://www.cottoninc.com/wp-content/uploads/2015/12/2012-Managing-Nematodes.pdf.
4 Koenning, S.R., Kirkpatrick, T.L., Starr, J.L., Wrather, J.A., Walker, N.R., and Mueller, J.D. 2004. Plant-parasitic nematodes attacking cotton in the United States. The American Phytopathological Society. Plant Disease Vol. 88 No. 2. https://apsjournals.apsnet.org/doi/pdfplus/10.1094/PDIS.2004.88.2.100.
Web sources verified 07/03/19.