Root-Knot Nematodes on Vegetables and Ornamentals
Root-knot nematodes cause galls on tubers and roots, leading
to stunted, wilted plants that are often off-color. Due to the
wide host range, managing root-knot nematodes means
taking the field temporarily out of production, and tilling it
periodically until populations are reduced.
Root-knot nematodes (Meloidogyne sp.) are microscopic roundworms that live in the soil and infect plant roots. There are more than 70 species described that occur around the world. Some species infect hundreds of different crops and weeds which makes it very difficult to manage them. The northern root-knot nematode (Meloidogyne hapla) is most common in Utah, along with a few other species that feed on vegetables and ornamentals.
Root-knot nematodes pass through four juvenile life stages before they become adults. The female second stage juvenile penetrates the root at the tip and moves up the root until it finds a suitable feeding site. There it establishes itself permanently, goes through the other two juvenile stages, and then changes its shape from worm-like to lemon-like.
When the nematodes become obese they frequently break through the root and deposit egg masses into the soil. One female root-knot nematode can produce several hundred eggs during her lifetime.
Male nematodes are not needed for reproduction in most root-knot, or Meloidogyne, species. The presence of male nematodes in the soil is a sign that the nematodes have been present in the field for a while. Not all Meloidogyne species have males, and their occurrence can depend on environmental conditions.
Above-ground symptoms of infection with root-knot nematodes often resemble symptoms of nutrient deficiency. Plants are yellow, small, stunted and wilt easily. Roots of affected plants often have galls. The galls, which contain the female nematodes, form due to hormones released by the females. The plants will transport more nutrients to the galls, providing more nutrition to the nematode. On root crops like carrots, the nematodes can cause forking and galls on the carrot.
If nematodes have been diagnosed in your field, management practices should be diligent due to the wide host range. Keeping the area fallow and weed-free and periodically roto-tilling it during the summer can help reduce the nematode populations over time to a level that allows vegetable or ornamental production. In a few years, however, nematode populations may build up again to a level where they cause significant damage. Samples with symptoms of root-knot nematodes can be sent to Claudia Nischwitz at the Utah Plant Pest Diagnostic Lab for confirmation.
-Claudia Nischwitz, Extension Plant Pathologist