There are no statistics for the world wide damage caused by nematodes, but it has been estimated that in the USA alone the damage done to crops is at least several hundred million dollars per year. The use of soil fumigants for nematode control during the past several years has often produced dramatic proof that nematodes in the soil can make the difference between a good crop and one not worth harvesting. Yield increases of 25% to 50% after soil fumigation are common. Experiments with soil fumigation have also made it evident that severe nematode damage can occur on a great variety of crops, including tree crops. The underground parts of plants, roots, tubers, corns, and rhizomes are more apt to be infected than above ground parts. Damage to plants attacked by nematodes is due primarily to the feeding of the nematodes on the plant tissues. The most common types of nematode damage are manifested as rotting of the attacked parts and adjacent tissue or the development of galls and other abnormal growths. Either can interfere with the orderly development of the plant and cause shortening of stems or roots, twisting, crinkling or death of parts of stems and leaves, and other abnormalities. The various kinds of nematode damage interfere with the growth of plants. Reduction in the size of the root system by rotting or galling restricts its efficiency in obtaining the food and water the plant must get from the soil. Root knot galls distort the tissue that has the function of conducting food and nutrients to the upper part of the plant. Damage to stems and leaves also interferes with normal growth. Consequently the yield of crop plants is reduced. Crippled plants cannot produce a high-quality crop. With some crops such as carrots and white potatoes, galls and rot caused by nematodes can make culls out of what would otherwise be saleable produce.