Integrated management of Meloidogyne incognita, the most economically damaging pathogen of cotton in the south-eastern United States

Authors: Davis, Richard; KEMERAIT, ROBERT - University Of Georgia

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/18/2021
Publication Date: 11/25/2021
Citation: Davis, R.F., Kemerait, R.C. 2021. Integrated management of Meloidogyne incognita, the most economically damaging pathogen of cotton in the south-eastern United States. In Sikor, R.A., Desaeger, J., Molendjik, L.P.G., editors. Integrated nematode management: state-of-the-art and visions for the future. Wallingford, UK: CABI International. p. 87-93. https://doi.org/10.1079/9781789247541.0013.
DOI: https://doi.org/10.1079/9781789247541.0013

Interpretive Summary: The Southern root-knot nematode, Meloidogyne incognita, causes greater economic damage to cotton in the southern US than any other single pathogen. Cotton is a major crop in all southeastern states. In 2019, M. incognita was estimated to reduce cotton yield by 7.0% in Georgia, 5.0% in Florida, 4.0% in South Carolina, 3.0% in Alabama, and 2.0% in North Carolina. Meloidogyne incognita is the most common root-knot nematode species in the Southeast and it can potentially be found anywhere cotton is grown in those states. Meloidogyne incognita has a wide host range that includes many potential rotation crops, common weeds, and cover crops. Peanut is not a host for M. incognita, but other common rotation options are hosts. Symptoms of damage on cotton may include stunting, wilting, and root galling, with interveinal chlorosis of leaves possible on severely damaged plants. In the southeastern coastal plain, up to five generations of M. incognita may be produced on cotton, and up to 2 generations may be produced on susceptible plants growing between cotton harvest and planting the following spring. The nematode survives the winter as eggs or J2 in the soil or in roots of susceptible plants. The basis for nematode management decisions is predictive sampling for comparison to action threshold levels. The greatest number of nematodes will typically be found in samples collected at the end of the season (October). Nematodes may be nearly undetectable in soil samples collected in mid-winter or spring. The action threshold in Georgia for M. incognita is 100 J2/100 cm3 soil. Crop rotation is effective in managing M. incognita if poor or non-host crops are used. A single year of growing a non- or poor-host crop effectively reduces M. incognita levels, but nematode levels quickly rebound when cotton is again grown. About half of the cotton hectarage in Georgia is rotated to some other crop after one year of cotton, about 40% is rotated after two years of cotton, and about 10% is never rotated out of cotton. The two most commonly used rotation crops in Georgia are peanut (a non-host for M. incognita) and corn (a good host). Nematicides are the primary method of nematode management in southeastern cotton production. Up to 75% of the cotton hectarage in Georgia is estimated to have one or more potentially damaging species of plant-parasitic nematode; however, about 20% is treated with a nematicide. Resistant cultivars are very effective in suppressing M. incognita and suffer far less damage than susceptible cultivars even under very high nematode pressure. In contrast to nematicides, resistance provides season-long suppression of M. incognita thereby providing benefit for a following crop. Up to 8% of the cotton hectarage in Georgia is planted with a resistant cultivar. Nematode management zones (MZ) divide fields into sections that are relatively uniform within a zone but different among zones, so sampling and managing each zone separately can more accurately target nematode management, especially with nematicides, thereby increasing profitability.

Technical Abstract: The Southern root-knot nematode, Meloidogyne incognita, causes greater economic damage to cotton in the southern US than any other single pathogen. Cotton is a major crop in all southeastern states. In 2019, M. incognita was estimated to reduce cotton yield by 7.0% in Georgia, 5.0% in Florida, 4.0% in South Carolina, 3.0% in Alabama, and 2.0% in North Carolina. Meloidogyne incognita is the most common root-knot nematode species in the Southeast and it can potentially be found anywhere cotton is grown in those states. Meloidogyne incognita has a wide host range that includes many potential rotation crops, common weeds, and cover crops. Peanut is not a host for M. incognita, but other common rotation options are hosts. Symptoms of damage on cotton may include stunting, wilting, and root galling, with interveinal chlorosis of leaves possible on severely damaged plants. In the southeastern coastal plain, up to five generations of M. incognita may be produced on cotton, and up to 2 generations may be produced on susceptible plants growing between cotton harvest and planting the following spring. The nematode survives the winter as eggs or J2 in the soil or in roots of susceptible plants. The basis for nematode management decisions is predictive sampling for comparison to action threshold levels. The greatest number of nematodes will typically be found in samples collected at the end of the season (October). Nematodes may be nearly undetectable in soil samples collected in mid-winter or spring. The action threshold in Georgia for M. incognita is 100 J2/100 cm3 soil. Crop rotation is effective in managing M. incognita if poor or non-host crops are used. A single year of growing a non- or poor-host crop effectively reduces M. incognita levels, but nematode levels quickly rebound when cotton is again grown. About half of the cotton hectarage in Georgia is rotated to some other crop after one year of cotton, about 40% is rotated after two years of cotton, and about 10% is never rotated out of cotton. The two most commonly used rotation crops in Georgia are peanut (a non-host for M. incognita) and corn (a good host). Nematicides are the primary method of nematode management in southeastern cotton production. Up to 75% of the cotton hectarage in Georgia is estimated to have one or more potentially damaging species of plant-parasitic nematode; however, about 20% is treated with a nematicide. Resistant cultivars are very effective in suppressing M. incognita and suffer far less damage than susceptible cultivars even under very high nematode pressure. In contrast to nematicides, resistance provides season-long suppression of M. incognita thereby providing benefit for a following crop. Up to 8% of the cotton hectarage in Georgia is planted with a resistant cultivar. Nematode management zones (MZ) divide fields into sections that are relatively uniform within a zone but different among zones, so sampling and managing each zone separately can more accurately target nematode management, especially with nematicides, thereby increasing profitability.