The causal fungus, Cercospora beticola, produces sclerotial masses in infected tissue, which probably are the source of overwintering inoculum. The spores, which are borne on the lesion surface, are wind-blown and provide the secondary inoculum. Spores may also be carried on the seed, but that source of primary inoculum is much less important than the debris of infected plants. When humidity is high, the spores germinate and send infection threads into the stomata to initiate the leaf lesions. Spores are not produced at low temperatures. Spread of the disease therefore is not great until midsummer. The fungus develops rapidly in the leaf for a short time until the plant develops a layer of cells, which wall the lesion off and limit its size. Hence the smallness and regularity of size of the spots.

The disease can be controlled by fungicidal sprays and dusts such as bordeaux mixture, fixed coppers, and the organic carbamates, but proper rotation is the most practical way. Resistant varieties of sugar beets have been developed. Among them are U. S. 215 x 216 and its derivatives.

DOWNY MILDEW is restricted almost entirely to Pacific coast areas. It attacks sugar beet, chard, and several species of wild beet, but not such related plants as spinach and lambs-quarters. It is more important on beet seed crops than on root crops.

The fungus, Peronospora schachtii, attacks plants in all stages. The leaves of seedlings are extensively yellowed and curl downward. Attacks on older leaves result in more restricted spots, which sometimes are ringed with darker pigmentation. If dry weather prevails after lesions begin, the spots may become dead and produce few spores. In wet weather the under side of the lesions becomes covered with spore-bearing growth of the fungus. The mycelium develops systemically in the cortex and invades the crown of the plant. Subsequent leaves are infected as they expand, and the entire crown becomes a rosette of small, distorted, mildewed leaves.

When crown-infected roots are planted the following spring for seed production, the floral stalk is systemically invaded and shows marked symptoms. Growth is severely retarded and distorted. Leaves are curled and thickened. Occasionally adventitious buds develop to give an effect of witches'-broom. Infected floral parts are swollen and distorted. Various affected parts may be covered with the downy fungus growth.

Downy mildew is serious only in cool weather when there are frequent showers or heavy dew or fog. Conidia germinate best at about 40 to 45 F., although germination will occur in range of 35 to 85 .

Sexual resting spores (oospores) are produced abundantly in infected tissue. Probably they carry the fungus over long periods of unfavorable conditions. The organism also is carried in seed which may initiate the disease in the spring. The chief source of primary inoculum, however, especially in seed-growing areas, is the over-wintering roots that were infected in the steckling beds. Adequate control measures have not been worked out but in the culture of steckling beds prevention of the disease by foliage fungicides is important.

MOSAIC and curly top are the worst virus diseases of beet in the United States.

Mosaic occurs in many other parts of the world, notably Europe, England, Australia, and New Zealand. It is conspicuously associated with seed production of beet and sugar beet, because of the cultural methods used in seed production. Beet roots for seed mostly are grown in steckling beds and transplanted to the seed row after overwintering either in the steckling bed or in pit or warehouse storage. Since steckling beds are planted some 2 or 3 months before seed harvest, there is an overlapping period between crops during which the virus is transmitted from seed plants to seedlings.

Because of a marked restriction in host range, overwintering in wild hosts is of little importance and the disease is of little importance in areas growing market beets only. The virus infects most species of the Chenopodiaceae the goosefoot family. Hosts in other families are pigweed, chickweed, zinnia, shepherds-purse, yellow sweetclover, and crimson clover. It can be found commonly on lambsquarters, pigweed, and spinach in beet-seed-growing areas.

Symptoms on beet consist of a transparency of the veins followed by many small rings that have red centers or are solid yellow spots with reddish borders. Concentric rings alternating pigmented and light areas are characteristic. Young leaves often show a Conspicuous, irregularly etched pattern along the veins. Infected plants usually develop an excessive amount of anthocyanin pigment and are thus easily detected in the field. With age, seed plants may develop considerable necrosis of leaves; defoliation then is severe. Leaves of infected plants often are leathery and markedly stunted and distorted.

Sap from infected beet plants loses its infectious properties when it is diluted 2,000 times, or allowed to age at room temperature for 2 or 3 days, or heated for 10 minutes in a water bath at 140 F.

The virus is transmitted from diseased to healthy plants by a number of aphids, notably the bean aphid (Aphis fabae) and the green peach aphid (Myzus persicae). The virus is not infectious enough to be spread on equipment. It is not seed-borne or soil-borne.

In seed-growing areas a marked measure of control can be had by growing the steckling beds in areas isolated from infected seed fields.

GLENN S. POUND is associate professor of plant pathology in the University of Wisconsin and collaborator with the Bureau of Plant Industry, Soils, and Agricultural Engineering of the Department of Agriculture. He is a native of Arkansas and has a bachelor's degree from the University of Arkansas. After receiving his doctorate from the University of Wisconsin in 1943 he spent 3 years at Mt. Vernon, Wash., studying diseases of vegetable seed crops in the Pacific Northwest. Since 1946 he has been engaged in research on vegetable crop diseases.