Diseases of Beets

Glenn S. Pound.

Garden beet, or red beet, is grown the country over as a common garden vegetable. It is grown as a canning crop on large acreages of the Great Lakes area, especially in Wisconsin and New York. Large acreages for fresh-market shipments are grown as winter crops in the South and Southwest, especially Texas and California. The production of beet seed represents an entirely different culture and is centered primarily in western Washington, Oregon, and California.

INTERNAL BLACK SPOT boron deficiency or heart rot is a common ailment of garden beet in many parts of the world. Applications of boron to the soil generally give good control, but it is still probably the worst disease of garden beet in the Northern States, where most of our canning beets are grown.

Young leaves are the first to show symptoms. They become redder and narrower than normal and stunted. Sometimes the leaf blades roll downward and die early. Growth of adventitious buds follows a similar pattern, and a cluster of dead leaves is left at the crown. The most conspicuous symptom on garden beet is the spotting of the root. The spots are black, corky areas, masses of dead cells that might be very small or involve much of the roots. The spots inside cannot be detected at harvest without cutting, and canners often have to reject fields where the disease is prevalent.

The first effect of boron deficiency in beet is one of increased cell division and growth, followed by death of the tissues and a reduction in the conductive tissue of the plant. Stunting or even death of the entire plant may result.

Many soils, especially alkaline soils or soils high in calcium, are naturally deficient in boron. Over-liming thus tends to increase the disease. In other soils the boron may be fixed and unavailable to the plant. The application of 40 to 75 pounds of borax to the acre before seeding will control the disease. The borax can be applied with the fertilizer. Boron in excess is extremely toxic. If it is applied in fertilizer beside the row, one must be careful to keep the fertilizer 2 or 3 inches away from the seed.

Sometimes black spot develops even when borax has been added to the soil, notably on heavy soils and when growth resumes after a drought. Apparently the boron becomes unavailable in dry weather. In such conditions the application of 10 pounds of borax to the foliage as a spray once or twice in midseason gives good control,

Some variation in susceptibility exists among varieties. Long Dark Blood is one of the least susceptible.

BLACK ROOT (damping-off), a seedling disease of beet, may be caused by any of a number of fungi. Beet and its relatives are very susceptible to fungus attack as seedlings because of the rapid growth of hypocotyl cells at or slightly below the soil line.

Several fungi may produce black root. The major ones are Rhizoctonia solani, Phoma betae, Aphanomyces cochhoides, and species of Pythium.

The organisms differ in importance according to localities concerned. In some areas Pythium debaryanum has been described as the primary incitant of black root; in other areas Aphanomyces is the chief incitant. The fungi differ in the time they attack seedlings. Pythium is the chief cause of preemergence damping-off. Usually Pythium effects are during the first 2 weeks after seeding. Phoma is carried on beet seed and may also cause preemergence damping-off. Phoma is not common on domestic seed, however, and it is thus of much less importance than the other fungi, all of which commonly inhabit the soil.

Symptoms of black root vary slightly according to the fungus involved. Pythium attacks any part of the germinating and emerging seedling, especially the taproot and hypocotyl, and turns them soft and black. Seedling leaves wilt and the plants topple over. It usually occurs in the very young seedling stage and rarely occurs after the first true leaf is formed.

Rhizoctonia attacks slightly older seedlings. It darkens the affected area, but the lesions are less extensive than those caused by Pythium, brown instead of black, and dry instead of soft. They also have definite margins. The fungus also incites a crown rot of mature sugar beets.

Aphanomyces attacks seedlings as Pythium does, but much later. It seldom causes preemergence damping-off. It also causes tip rot, a rot of mature sugar beet.

Aphanomyces, Pythium, and Rhizoctonia all persist for a number of years in the soil. Close cropping of soil to beets increases the incidence of disease. A high level of soil fertility helps control black root, probably by producing rapid and sturdy growth of the seedlings. The disease is most severe in rainy seasons. Pythium attacks are most severe at temperatures of about 55 to 70 F.; those of Rhizoctonia at about 60 to 85 ; and those of Aphanomyces at about 65 to 90 .

Pythium can be controlled by such seed protectants as New Improved Ceresan, Arasan, Phygon, and copper oxide. They have less effect on Rhizoctonia and little or no effect on Aphanomyces because it attacks so late. Phoma can be eradicated from seed by treatment with hot water, but that may not be practical. L. D. Leach, of the University of California, has shown that spraying seed with a suspension of New Improved Ceresan greatly reduces the amount of seed transmission.

CERCOSPORA LEAF SPOT is the most common and most destructive leaf disease of beet and sugar beet. In the United States it is prevalent only in areas that are relatively humid or get regular rains during the growing season. In the Midwest it may be serious in rainy seasons and almost absent in dry seasons. It is generally much less serious on garden beet than on sugar beet. The fungus can attack Amaranthus, lambsquarters, lettuce, celery, sweetpotato, dock, soybean, spinach, potato, and other plants.