A moderate amount of root knot resistance is associated with fusarium resistance in varieties developed in the Southeast and selected on wilt- and nematode-infested soils. In the process of selecting for fusarium resistance and high yield in segregating progenies; moderate resistance to root knot is obtained without specific effort on the part of the breeder. This resistance contributes to the fusarium resistance and to the yield of such lines. High resistance to root knot is not present in any upland varieties. However, there are considerable differences between the most susceptible and the most resistant ones. Varieties combining both fusarium resistance and moderate root knot resistance are Stonewilt, Coker too wilt, and Plains. Several varieties considered susceptible to root knot are Rowden, Miller, Deltapine, Bobshaw, Stoneville, Empire, and Pandora.

A SEARCH for high resistance to root knot was made at the Alabama Agricultural Experiment Station in 1951. A number of the world cotton species and many types and varieties were planted, and the roots were later examined for size and abundance of galls. Several sources of resistance were found, the most promising of which were Gossypium barbadense var. darwinii and two wild cottons from Mexico. The latter two introductions from Mexico are much like upland (G. hirsutum) but are not productive. These three were crossed and back-crossed to productive upland varieties. The segregating progenies will be selected for root knot resistance and further backcrossed. Eventually high root knot resistance in combination with desirable agronomic characters will be obtained. Improved root knot resistance will increase the yields of varieties grown on infested soils and should also improve the resistance to fusarium wilt.

THE USE OF BALANCED FERTILIZERS to maintain a vigorous growth of cotton plants is an important cultural practice to prevent losses from cotton Wilt. Potash tends to reduce wilt losses.

Nitrogen and phosphorus tend to increase wilt within certain limits. The proper balance of nitrogen, phosphorus, and potash gives the maximum yields and best control of wilt when no one of the three elements is deficient. Cotton rust, or potash deficiency, was early confused with cotton wilt. George F. Atkinson discovered that ample application of potash prevented the occurrence of rust. Rust on cotton continued to cause serious losses and increased the losses from wilt until 1926, when American sources of potash were developed, which provided ample supplies at a reasonable cost.

NEMATOCIDES can control fusarium wilt and nematodes and thereby can double yields of resistant varieties and triple and quadruple the yields of susceptible varieties grown on soils heavily infested by both pathogens. In experiments in Alabama in 1947, I learned that wilt is controlled indirectly by destroying the nematodes. The yields are increased as a result of control of both the wilt and nematodes. On treated plots better stands are maintained, the plants grow off more rapidly, grow larger, and produce greater yields.

Most economical control is obtained by applying the material in the row at the rate of 6 to 8 gallons an acre a few days before planting. Materials giving satisfactory control are ethylene dibromide and a mixture of dichloropropene and dichloropropane. Their trade names are Dowfume W-40 and D D. Row application gives control of nematodes in a zone near the young plants. Once the plants are established and growing rapidly, later nematode infections do little damage to the crop. Annual applications are necessary if only the row application is made.

ROTATING COTTON with crops that reduce the amount of root knot is a cultural practice of value in reducing wilt losses and increasing yields. Crops that reduce root knot nematodes are grasses, sorghum, small grains, corn, peanuts, crotalaria, velvetbeans, alfalfa, and nematode-resistant cowpeas.

Several crops that are particularly susceptible to root knot tend to intensify wilt and nematode losses. Among them are cowpeas susceptible to root knot, annual lespedezas, sweet-potatoes, and tobacco.

Crops grown during mild winters for green manure sometimes increase populations of root knot to the extent of causing increased losses in the cotton crop that follows them. Blue lupine, Austrian winter peas, and vetch are examples. On the contrary, increased organic matter is beneficial in improving yields and reducing wilt losses.

Rotations help to control other diseases of cotton. An example is ascochyta blight of young plants, which sometimes becomes epidemic. Rotation is likewise of value against bacterial blight infections in the Southwest and irrigated valleys, where plant refuse is not decayed over winter.

The rotation of cotton with other crops has not become a widely used practice. Farmers are reluctant to follow some other crops with cotton, particularly peanuts and hay crops, which exhaust the soils of some minerals to the extent that yields of cotton may be reduced. Other reasons may have to do with the accessibility of the land to the house, weeds, and the tendency to select the most productive land for cotton.

ALBERT L. SMITH is a graduate of Oklahoma Agricultural and Mechanical College and the University of Wisconsin. He joined the Department of Agriculture as a pathologist in 1936 to work on cotton diseases and breeding for disease resistance. Most of his time has been devoted to studies on fusarium wilt and nematode disease of cotton. Plains, a wilt-resistant variety of cotton was developed by him and released in 1949. He is stationed at the Alabama Polytechnic Institute in Auburn.