Diseases of watermelon (
Root-knot nematode
The Root-knot nematode, Meloidogyne incognita, infects all cucurbits and many other plants. This nematode is widespread in Arizona, but is usually found in sandy or sandy loam soils. It is an obligate parasite that must complete its life cycle in a plant host, but eggs are persistent and can remain inactive in the absence of a host and/or fallow for months or years.
As M. incognita larvae enter the plant root, feed and mature, the surrounding cells of the plant root increase in size and divide causing swellings, often referred to as galls, on the roots. The flow of nutrient and water is restricted, and plants wilt quickly when water becomes limiting. If plants are infected when young, they are often severely stunted and chlorotic. Infected vines rarely die, but are generally not productive.
Because of the nematodes wide host range, control is difficult. Cotton, sorghum, corn, and beans, among many other crops, are all hosts and should not be rotated with watermelon when M. incognita is a problem. Rotations to alfalfa and oats, which are not hosts, are effective, especially in multiple year rotations. Preplant soil fumigation with 1,3 Dichloropropene or metam-sodium is also effective in reducing early infections. Soil solarization is an option for small areas that can be effectively tarped for at least 6 weeks in summer. More information on control strategies and solarization can be obtained from:
http://cals.arizona.edu/yavapai/anr/hort/byg/archive/soilsolarization.html
http://edis.ifas.ufl.edu/pdffiles/CV/CV11200.pdf
February 10, 2003