Rain drops splash spores from the soil onto the plants, from leaf to leaf, and from plant to plant. Infection is favored by moderate temperature and high moisture. The fungi become more easily established in tissues affected by some kind of injury. There are no obvious symptoms of anthracnose infection in summer.

Essentially, the organism exists as a saprophyte in injured tissues. It may also live on honeydew on leaf surfaces. During dry periods it remains dormant and survives for long periods as mycelium in tissues or appressoria attached to the surface. With the return of wet periods it builds up to epidemic proportions and becomes destructive on the bolls.

Infections on the boll gain entrance through the corolla, through bacterial blight lesions or insect wounds,through the sutures separating the loculi, or directly through the uninjured surface. The lint and seed of bolls beginning to open are invaded directly to produce tight lock without invasion going through the boll wall.

Anthracnose seedling blight can be readily controlled by seed-treatment disinfectants. Beginning in 1936 uniform seed-treatment tests were conducted across the Cotton Belt by members of the cotton disease council of the southern section of the American Phytopathological Society. An average increase of 30 percent in emerged seedlings was obtained from application of dust disinfectants. After testing a large number of materials, the committee recommended the use of organic mercury compounds (5 percent Ceresan and Ceresan M) and zinc pentachlorophenate (Dow 9 B). Those two volatile materials largely eliminate surface-borne anthracnose spores and give some protection to the young seedling in the soil. The council has also recommended the use of slurry treaters to replace the dust applicators. The slurry application largely eliminates the obnoxious dusts and reduces the danger to workers handling seed in processing plants.

Anthracnose boll rot, tight lock, and fiber deterioration still are serious problems. Losses are greatest in the Coastal Plain where cotton opens earlier and during the September storm period.

Earlier recommendations for control of anthracnose boll rot included 1-year rotations to eliminate winter carryover of the organism on crop refuse and the selection of planting seed from healthy bolls or from noninfested fields. It was found that the seed-borne fungus died out or was greatly reduced if the seed were stored for 18 months. Thus 2- or 3-year-old planting seed were recommended. Fall plowing was found beneficial for destruction of the stalks and other crop refuse before spring planting where rotations were not possible. Those measures, while effective, were not generally practical or widely adopted by growers.

Defoliation can be the most effective method of reducing boll rot losses from anthracnose and other rots.

Good defoliation is obtained when calcium cyanamide is applied as a dust at the rate of 30 pounds an acre. Removal of the leaves permits rapid drying of the bolls and lint after rains and dews and reduces boll and fiber losses. Other practices of value in reducing boll damage are the planting of varieties with smaller leaves and open-type growth, limiting vegetative growth of the cotton plant by reducing nitrogen applications, controlling insects that damage bolls, and controlling grass and weeds that hinder air circulation.

Varieties have different degrees of resistance to the pink boll rot phase of anthracnose. Somewhat resistant varieties are Toole, Dixie, Dillon, Express, Rowden, Cleveland, and Deltapine. Other varieties considered susceptible are Cook, Half and Half, Hi-Bred, Lone Star, Wilds, Triumph, Trice, and Stoneville. The lack of recent severe infestations of anthracnose boll rot has prevented a classification for resistance of newly introduced varieties. The diminution in anthracnose boll rot may be attributed partly to the discontinued production of many of the older susceptible types in favor of the newer, less vegetative, earlier, resistant ones.

Resistance to anthracnose seedling blight has not been investigated thoroughly. As considerable success has been achieved in controlling seedling blights with dust disinfectants, an intensive effort has not been made to obtain resistant varieties. It is generally agreed that all commercial varieties are quite susceptible in the seedling stage.

ASCOCHYTA BLIGHT, commonly called wet-weather blight or wet-weather canker, is the most sporadic of all cotton diseases. The causal organism is Ascochyta gossypii.

The distribution of ascochyta blight parallels the distribution of anthracnose. It occurs in all cotton States from Virginia westward to the 40-inch rainfall line in eastern Texas and Oklahoma. In 1950, a relatively wet year, it was reported prevalent in central Texas and as far west as Lubbock. The most serious occurrences of the disease have been in the Piedmont areas of the Carolinas and Georgia and in the northern parts of Alabama, Mississippi, and central Arkansas.

Losses from the blight result primarily from reduction or loss of stands in the young plant stage. These losses were generally not recognized by pathologists until 1947. From 1947 through 1950, a 4-year period of relatively heavier rainfall years, losses were common and serious in areas involving the northern parts of the Carolinas, Georgia, Alabama, and Mississippi. Serious losses occur during periods unfavorable for plant growth brought about by moist, cool weather. Plants 3 to 8 weeks old are particularly susceptible. The more spectacular but less damaging stem canker has occurred sporadically at infrequent intervals since 1914. Additional but minor losses are caused by leaf blighting and partial defoliation of older plants and boll rotting.

The earliest infections are produced primarily from spores that overwinter on the old plant refuse in the field and are splashed by rain or blown to the leaf surfaces. The spores also over-winter on planting seed that is not treated with a disinfectant.

Earliest symptoms are small, circular white spots on cotyledons and leaves. The lesions enlarge, often coalesce, become brown and roughened, and often fall out, leaving a ragged appearance. Cotyledons and leaves often are defoliated and the young stems are left bare. Additional infections girdle the stems and kill the terminal buds and adjacent stem tissues; the result is loss of stands. From June to August, conspicuous stem cankers occur at the branch axils and center about the stipules. Cankers are from one-half inch to an inch long, dark brown, and ragged at the edges. Sometimes the stems or branches are killed by cankers, but usually stem cankers cause minor damage.

Stem cankers occur only during periods of several consecutive days of cloudy, wet weather. With the return of dry, hot weather, the disease is checked and canker symptoms are quickly obscured by new growth. During wet weather in July and August, older leaves frequently become infected. The lesions may spread quickly and consume most of the leaf area, so that there is extensive defoliation, particularly of the lower leaves. Boll rot lesions are rough, circular, and brownish. Invasion of the seed and lint complete destruction of the boll.

Excellent control of ascochyta seedling blight is had by seed treatment and crop rotation. Primary infections originating from seed-borne spores are largely eliminated by seed treatment with disinfectants. Rotation eliminates the overwintering inoculum that originates in the cotton plant refuse from the previous crop, and excellent control of seedling disease phases is obtained. Partial, but generally satisfactory, control is obtained by plowing old stalks and leaves under deeply in the fall and planting flat to leave such material buried. Other practices that reduce the amount of old plant refuse left on the surface of the soil at planting time may be beneficial.

We have little information on resistance in varieties. Studies made at the Georgia Agricultural Experiment Station in 1947 indicate Empire, Deltapine 15, and Stoneville 2B have slightly more resistance to stem canker in older plants than several other commercial varieties. No varieties have enough resistance to withstand the seedling blight attacks, which are the most destructive phase of the disease.

BACTERIAL BLIGHT of cotton was first described in 1892 by George F. Atkinson in studies conducted at the Alabama Agricultural Experiment Station. He named the disease angular leaf spot and found a bacterium to be the causal agent. The thin-walled parenchyma cells of leaves, stems, and bolls are attacked. The stems may be girdled and show the "black arm" symptoms. Spread of the bacteria along the leaf veins is commonly called vein blight. Lesions on bolls are commonly called boll rot or boll blight. The common name bacterial blight has been adopted to include all those symptoms. The causal organism is Xanthomonas malvaceorum.

Bacterial blight is prevalent in all cotton-producing areas. It may have originated in India, the center of origin of Old World cottons. It apparently has been associated with cotton in the United States from the beginning of cotton culture. The disease is worst in the subhumid and semiarid areas of the Cotton Belt where the rainfall varies from 10 to 30 inches. Epidemics occur almost every year in the High Plains of west Texas, in the Pecos and Rio Grande Valleys of New Mexico and Texas, and in Arizona and Oklahoma. The disease has been of minor importance in California. In the mid-South and Southeastern States the occurrence is universal, but damage is less serious and more sporadic. Winds of cyclonic intensity accompanied by rain sometimes cause epidemics of the disease over large areas in the Southeast.

Losses result from reduction in stand, defoliation of leaves, stem blighting, shedding of small bolls, boll rotting, and reduction in grade from lint staining. The American-Egyptian irrigated varieties of the Southwest may become complete crop failures during serious outbreaks. In 1949 the yield reduction was estimated at 35 to 50 percent on 40,000 acres in New Mexico. For upland varieties in the United States as a whole the damage is from 1 to 2 percent of the crop. The southwestern upland crop, from Oklahoma westward to Arizona, is consistently affected to the extent that bacterial blight is considered the major disease problem. Besides lower yields largely due to leaf defoliation, the yellow bacterial slime stains the fibers and lowers the grade and price received by the grower. In the South and Southeastern States the blight bacteria provide primary lesions on bolls through which the boll-rotting Diplodia, Alternaria, Glomerella, Fusarium, and other fungi gain entrance and rot the seed and fiber.