How can I manage nematodes in potatoes?
Answer: Nematodes are microscopic roundworms found in many habitats. Nematodes are the most abundant multicellular organisms on Earth. Most are beneficial members of their ecosystems, but a few are economic parasites of plants. The Columbia, Stubby, and Northern Root Knot nematodes are common in Western organic potato systems and are the leading cause of soil fumigation in commercial potato production in the Northwest.Root knot nematode feeding reduces the vigor of plants and causes blemishes on tubers. Infection of tubers by the Columbia and stubby root knot nematode often results in the formation of galls that appear as knobs or swellings on the tuber surface and affect marketability. Root knot nematode larvae invade roots or tubers, establish feeding sites and develop into the adult stage. Adult females are swollen, sedentary and lay eggs in a gelatinous matrix on or just below the root surface. These eggs hatch and larvae invade other roots and tubers. Feeding by root knot nematode eliminates the possibility of exportation since infected potatoes are banned in many countries.There are recent promising developments with biofumigation using brassica mustard cover crops in a rotation before potatoes. Brassica crops such as rapeseed and mustard contain active chemicals called glucosinolates. The breakdown of these chemicals has been shown to suppress some soilborne diseases, nematodes and weed seeds. The best strategy for the ultimate suppression of soilborne diseases and nematodes is selecting a species of mustard that produces large amounts of biomass and glucosinolates.Also, before incorporating, chop the green manure with a rotary mower or a high-speed flail chopper. The breakdown of the biofumigant seems to be better in moist soils, so irrigate following incorporation or time incorporation to occur with a rain. Jack Brown, a plant breeder specializing in brassicas at the University of Idaho, has released two biofumigant varieties: Humus rapeseed and IdaGold mustard. Each variety contains elevated levels of glucosinolates. For more information on these varieties, see the ATTRA publication Nematodes: Alternative Controls. To learn more, consult the ATTRA publication Potatoes: Organic Production and Marketing. This publication outlines approaches to organic and sustainable potato production. Practices include fertility and nutrient management; organic and biorational pest management for insects, diseases and weeds; and storage and marketing.