Research workers have gotten widely different results in tests of fungicides. In British Columbia and England bordeaux mixture gave good control, and poor control was had with sulfur fungicides. In the United States, Egypt, Belgium, and Poland, opposite results have been obtained. The explanation might be that bordeaux mixture is ineffective when average maximum temperatures and other factors favor good rust development; when the average maximum temperature is above the favorable range or if other conditions are unfavorable for the rust, bordeaux is effective.

Research by Dimock in New York and Baker in California helps explain these discrepancies. They found that under semiarid conditions, bordeaux mixture fails to control either rust or the damage from desiccation caused by the rust; in humid and rainy conditions, however, serious plant damage is prevented because invasion of secondary fungi is controlled by bordeaux although rust is not controlled.

An example of apparent rust control was the effectiveness of both Bioquin 1 and bordeaux mixture at Ithaca, N. Y. Rust control with the two materials was poor there, but the secondary fungi, which invade through the rust pustules, were effectively controlled; and the plants remained relatively normal in appearance and bloomed profusely.

At Los Angeles the bordeaux-sprayed plants were severely damaged by desiccation of the rust-invaded tissues. Zineb gave excellent control at all places; rosin-lime-sulfur, good control; and wettable sulfur, poor control.

PHYLLOSTICTA BLIGHT, caused by the fungus Phyllosticta antirrhini, affects outdoor snapdragons. Occasionally it attacks those grown in greenhouses. Plants of all ages and varieties are susceptible.

The disease is characterized by large, circular, dark-brown or black zonate spots, which are small and cream-colored at first and darken as they age. Usually they become zonate because of an abundance of black dots pycnidia that develop in rings. Leaves attacked when young become distorted and curled; the whole leaf may die but clings to the stem. Dark-green, water-soaked spots form on the stem several inches from the tip. The spots spread rapidly and girdle the stem. In a few days the affected tissue shows a firm, dark-brown rot. These stem lesions soon become covered with numerous pycnidia, arranged over the surface in close circles. The stem lesions on a young seedling may girdle the plant near the base and cause rapid wilting and death.

Blight apparently occurs wherever snapdragons grow. In England it is more common as a stem disease than as a foliage disease. The fungus may overwinter in plant debris or on plants that live through the winter. The disease, like most leaf diseases, is favored by a moist atmosphere. Temperatures below 60 are unfavorable for the development of phyllosticta blight. Consequently it is most serious in summer.

Control consists of cleaning up all debris of snapdragon plants in the fall and spraying the plants during the growing season with bordeaux 4-4-50 (4 pounds of copper sulfate, 4 pounds of lime, and water to make 50 gallons). In the greenhouse, surface watering and temperatures below 60 are recommended.

BOTRYTIS BLIGHT, caused by Botrytis cinerea, frequently causes serious losses in greenhouse snapdragons and in coastal seed fields. It occurs most commonly in poorly managed greenhouses where the humidity is often excessive.

It causes the flower spikes to wilt. When one examines such spikes, he finds tan areas on the stem near the lowest flowers or the base of the shoot. Those areas enlarge rapidly, girdling the stem and causing the death of the spike. Infection takes place through old blossoms; through the glandular trichomes, which occur on the flowering part of the stem; through wounds; or through tissues previously attacked by other diseases, such as rust or powdery mildew. The gray-brown spore masses soon appear if humidity is high.

Control involves cutting the spikes as soon as they are marketable, removing infected parts, cleaning up all plant debris, and avoiding excessive humidities by proper control of greenhouse temperature and ventilation.

ANTHRACNOSE, caused by the fungus Colletotrichum antirrhini, is more destructive in the greenhouse in fall and spring than in winter. It is most conspicuous outside in August and September.

Many elliptical sunken spots are produced on the stem. Round dead spots appear on the leaves. At first the spots on the stems are dirty white, with a narrow, brown or reddish-brown border. Minute black acervuli appear later at the centers of the spots. The fungus may attack stems of all ages. Several large spots may girdle the plant at the base. A single large spot may cause death of a succulent terminal part. Anthracnose can be controlled out-of-doors by spraying with bordeaux mixture or other good fungicides, such as zineb, ferbam, lime-sulfur, or wettable sulfur. In the greenhouse, one can control it simply by keeping the foliage dry.

AMONG THE OTHER DISEASES of snapdragons are:

POWDERY MILDEW (Oidium species) has been confined to greenhouse-grown snapdragons in the United States. It is characterized by white powdery growth on both leaf surfaces and occasionally on young stems. It can be controlled by sulfur dust or a wettable sulfur spray plus a suitable spreader to insure complete coverage.

DOWNY MILDEW (Peronospora antirrhini) is most common on seedlings, on which it causes a characteristic paling and downward marginal curvature of affected leaves. The terminal-shoot growth is checked and the disease can cause the death of all aerial parts. The fungus sporulates on the lower surface of leaves as a white, sparse downy growth.

ROOT KNOT (Meloidogyne species) is evidenced as gall-like swellings on the roots. This nematode disease is controlled by soil sterilization.

STEM ROT AND WILT (Phytophthora cactorum) is characterized by a girdling of the stem at the root level, followed by wilting and death. The disease can be controlled by soil sterilization.

W. D. MCCLELLAN, a native of California, studied plant pathology at the University of California and Cornell University. He was on the staff of the University of Maryland and the Bureau of Plant Industry, Soils, and Agricultural Engineering before he became director of research for the Mid-State Chemical Supply Co. at Lindsay, Calif., in 1951.