Use of Root Gall Ratings to Determine High Risk Zones in Cotton Fields Infested by Meloidogyne incognita

Farmers growing cotton (Gossypium hirsutum L.) need a reliable, accurate, and inexpensive method for mapping areas of potentially high risk from root-knot nematodes (RKN) [Meloidogyne incognita (Kofoid & White) Chitwood] within individual fields for site-specific application of nematicides. Evaluation of postharvest cotton roots for galling severity due to RKN may be an alternative to soil analysis for nematodes for developing these maps. The main objectives of this study were to determine the relationship between yield of cotton and root galling severity the year before planting, and the estimated costs per hectare for rating root galling severity compared with that of conventional soil sampling using a 15-m grid spacing. There was a significant negative correlation between root galling severity in October and cotton yield the next 2 yr, indicating galling severity may be a useful indicator of the potential threat of RKN to crop performance for more than 1 yr. The estimated costs for assessing galling severity, $183 ha−1, were much less than for soil analysis for nematodes, $968 ha−1 Unfortunately, maps based on galling severity will only be useful guides for site-specific application of nematicides if RKN is the only economically important cotton parasitic nematode present. More accurate and less expensive ways of sampling for RKN are needed to identify within-field areas where the risk of nematode-induced yield loss is high.