In countries where freezing weather does not occur and the cane grows throughout the year, the fungus is always active. Where freezes occur, however, there may be periods of weeks or months when no living portion of the plant is above ground. Then the fungus survives in trash or crop refuse in the planted seed pieces or on stubble from the previous crop. In the spring when growth starts, infection of the new leaves occurs from such overwintering sources. Apparently the fungus does not survive in the soil.

After the fungus invades the tissues of the stalk, the mycelium may spread sidewise and up and down from cell to cell. More rapid longitudinal spread may occur by migration of the spores through the vascular bundles.

Varieties differ in the extent and rapidity of the spread of the spores in this way, because some have many bundles that are continuous through the nodes from one internode to the other. In other varieties few bundles are continuous. In varieties with a large number of continuous bundles, the spores may spread through the entire stalk; if the bundles are discontinuous, the fungus may be checked for a time at the nodes. Thus it happens that some varieties whose tissues have little resistance may not be seriously damaged by the disease because of the checking of longitudinal spread through the nodes. This type of resistance offers less protection, however, if the variety is highly susceptible to infection at the nodes, or if the stalk is seriously damaged by the stalk borer, since the tunnels of this insect in successive internodes offer a ready means of separate infection.

Injury to seed cuttings by red rot is not limited to conditions of excessive soil moisture that often prevail in heavy soils, but they do favor greatly the development of the disease. Often the severity of red rot then is also associated with injury by pythium root rot. If the rootlets arising from the seed cutting are destroyed by root rot during germination, the development of the new shoot may be retarded. If red rot has invaded the seed piece, the spread of the disease during the period of delayed establishment of the new plant may kill the young shoots. Thus the degree of injury from red rot may be greatly influenced by the susceptibility of the variety to root rot. A variety that is susceptible to red rot but resistant to root rot may be less injured than one that is only moderately resistant to red rot but very susceptible to root rot.

A common source of infection of the stalk by red rot is through the tunnels of the moth borer. Frequently the degree of injury to mill cane by the disease depends on the extent of infestation by this insect particularly in areas like Louisiana, where during the relatively short growing season infections of the stalk (other than those that occur from insect injury) do not have time to develop sufficiently to cause important damage to the cane before it is milled. Red rot damage to seed cuttings also is often increased by borer damage and in some varieties may relate directly to the extent of infestation by the moth borer.

Infection of the underground parts of the stem after harvest, from which the stubble or ratoon crops arise, may occur through the tunnels of the sugarcane weevil (Anacentrinus subnudus). At times germination of the buds on the stubbles may be impaired by the combined effects of insect and disease injury.

As a seed-rotting disease, red rot is hard to control. Because infection of the stalk to be used for seed has occurred to a great extent before the time of planting, the fungus is largely beyond the reach of fungicides that control many seed-borne diseases of other crops.

Heat treatments that might reduce or eliminate the infection in the stalk are not economically feasible for large-scale use. Furthermore, the fungus is extremely variable; it comprises many parasitic races that apparently are being continually increased by mutation or hybridization. Thus there can be no certainty of the permanence of resistance because of the possibility of the development of virulent, specialized races on initially resistant varieties.

Also, red rot as a seed-rotting disease is favored by the very conditions that retard germination and growth of the cane plant. The balance may be thrown so far in favor of the parasite that ordinarily resistant varieties may at times be seriously damaged by the disease.

Finally, breeding for resistance to red rot is handicapped by the lack in parent material of the high degree of resistance or immunity that is available for some other diseases, such as mosaic or root rot.

Effective control, however, depends on the planting of resistant varieties. Progress has been made in developing resistant varieties under the breeding program of the Department in cooperation with State agricultural experiment stations. The varieties C. P. 36/ 105, C. P. 44/101, and C. P. 44/155, Important commercial varieties in Louisiana, are resistant to red rot, as is C. P. 36/111, recommended for sirup Production in Mississippi and other areas of the Gulf States.

Where it is feasible to do so, red rot injury can be avoided to a great extent by planting cane at a time that favors early germination and establishment of the new plants. In Louisiana, for example, part of the acreage commonly is planted in August, when high temperatures usually result in quick germination and establishment of stands. That practice avoids the danger of the injury that accompanies planting in fall, when there may be little growth for several weeks.

Improvement of drainage and the use of resistant varieties in heavy or inadequately drained soils lessen the hazards of injury. The use of seed cane that is as free as possible of borer infestation is desirable to avoid loss from both insects and red rot.

E. V. ABBOTT is a pathologist in the division of sugar plant investigations, Bureau of Plant Industry, Soils, and Agricultural Engineering, and superintendent of the United States Sugar Plant Field Station, Houma, La.