|Vories, Earl - Earl|
Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2010
Publication Date: 11/1/2010
Citation: Wrather, J.A., Stevens, W.E., Vories, E.D., Kirkpatrick, T.L., Mueller, J.D., Mauromoustakos, A. 2010. The use of root gall ratings to determine high risk zones in cotton fields infested by Meloidogyne Incognita. Crop Science. 50(6):2575-2579. Interpretive Summary: Parasitic nematodes were found in cotton fields in Missouri and other areas at high enough populations to reduce yield. Chemicals to control nematodes, called nematicides, are quite expensive, so cotton farmers need a reliable, accurate, and inexpensive method for determining the potential threat within individual fields for site specific application of nematicides. Evaluation of cotton roots at harvest for injury (galling) may be an acceptable and less expensive alternative to soil analysis for determining nematode population distribution in fields and a study was conducted to determine the relationship between yield of cotton and root galling severity. There was a significant correlation between root galling severity and cotton yield, indicating galling severity may be a useful indicator of the potential threat to crop performance. Root galling provided an immediate indication of the distribution of the nematodes and the severity of the crop damage without soil sampling and laboratory analysis. Development of these procedures will benefit farmers by reducing their nematicide costs and will benefit everyone by identifying the precise areas where nematicides are needed and eliminating application to other areas.
Technical Abstract: Cotton farmers need a reliable, accurate, and inexpensive method for determining the potential threat of root-knot nematodes (RKN) to cotton within individual fields for site specific application of nematicides. Evaluation of cotton roots for RKN galling at harvest may be an alternative to soil analysis for nematodes for mapping RKN distribution in fields. A study was conducted to determine the relationship between yield of cotton and root galling severity the year prior to planting, the percent of roots that should be examined for galling within a field site or grid to estimate galling severity, and the estimated costs/acre for rating root galling severity compared with that of conventional soil sampling. There was a significant negative correlation between root galling severity in October and cotton yield the next two years, indicating galling severity may be a useful indicator of the potential threat of RKN to crop performance for more than one year. However, a density map based on root galling would not be useful for six years because the map of RKN density at this site changed dramatically during this time. The half width confidence interval (HWCI) for an estimate of root galling severity to true galling severity declined as the percent of plant roots examined increased. The estimated costs for assessing galling severity, $172 ha-1, were much less than for assessing soil population density of J2, $946 ha-1. Root-knot nematode density maps based on root galling severity may be an alternative to development of density maps based on soil analysis for nematodes. Galling severity ratings were more reliable for estimating RKN actual damage potential to cotton than soil population density of this nematode in this study. Root galling provided an immediate visual indication both of the distribution of the nematodes within the field and the severity of the nematode-induced crop damage without the need for soil sampling and laboratory analysis. Unfortunately, maps based on galling severity will only be useful guides for site-specific application of nematicides or other remediation tactics if root-knot nematode is the only economically important cotton parasitic nematode present. More accurate and less labor-intensive/expensive ways are needed to identify within-field areas where the risk of nematode-induced yield loss is high.