I treated an entire isolated planting at St. Francisville, La., with 400 pounds of cyanamide an acre in 1942. Petal blight appeared later and failed to become as severe as in previous years. I could not determine whether infection originated from apothecia that escaped the treatment or from conidia from another planting. I observed no injury in azaleas and no lasting injury in other plants.

Dr. Brierley pointed out that two factors weigh against the practical use of a material suppressing apothecial formation: The danger of injury to azaleas or other plants grown in association with them and the need for application on a community-wide basis to accomplish significant reduction of the disease.

During the azalea seasons of 1944 and 1945, Cynthia Westcott represented the Department of Agriculture at Spring Hill, Ala. She assembled a number of new and old fungicides. These she tested in the laboratory and garden as protectants against conidia) infection. Two offered good Control of petal blight with a minimum of discoloration or injury to the flowers. They were: (1) Dithane D-14 (nabam), 1 1/3 quarts; zinc sulfate, 1 pound; lime, one-half pound; and Triton B-1956, 1 fluid ounce to 100 gallons of water; and (2) Phygon (2,3-dichloro-1,4-napthoquinone), 1 pound to 100 gallons of water.

Applications were made three times a week. Satisfactory control resulted on sprayed flowers even when only half a plant was sprayed and infection was severe on the other half.

Those preparations were used in 1946 in a number of parks, estates, and gardens. All reported excellent control, but some found objectionable injury to the flowers. I followed Dr. Westcott at Spring Hill in 1946. I tested other fungicides, wetting agents, concentrations, and frequencies of application, and studied the nature of the flower injury.

Nabam (Dithane D-14 and Parzate Liquid) and zineb (Dithane Z-78 and Parzate) have been outstanding fungicides against petal blight in comparison with other materials. Di-thane D-14 and Parzate Liquid sprays were prepared at the strength Dr. Westcott used. Dithane Z-78 and Parzate were used at the rate of 1.4 pounds to 100 gallons. A reduction in the concentration was considered desirable to reduce spray residue on the flowers and possibility of injury. Dithane D-14, 0-9 quart; zinc sulfate, 0.67 pound; lime, 0.34 pound; and Triton B-1956, 1 fluid ounce to 100 gallons, was found satisfactory. The quantity of zineb (Parzate and Dithane Z-78) was successfully reduced to 0.97 pound to 100 gallons.

Santomerse S (2 fluid ounces in 100 gallons) or Dreft (4 ounces in 100 gallons) were found to be satisfactory wetting agents to replace Triton B-1956 in making the Dithane D-14 spray. The wetting agents cause the spray to spread over the flowers in a film instead of forming drops that roll off. Lime is not essential in the spray.

Tests were conducted for 4 years with Dithane D-14 and for 2 years with Phygon, using one, two, and three applications a week. Spraying three times a week gave consistently better results than spraying twice, although many gardeners would have been satisfied with the control obtained with the latter. One application a week was unsatisfactory.

Dr. Westcott found some injury to azalea flowers by Phygon, but did not consider it objectionable in view of the control obtained. In later tests and in the hands of some gardeners, the injury proved objectionable, particularly after three or more applications of the material. Injury consisted of bleaching and burning of the flowers from the margin inward. It was present to a lesser extent when the concentration was reduced beyond that affording satisfactory control. Some other quinone compounds produced similar injury. We no longer recommended Phygon.

In preparing the Dithane D-4 spray, Dr. Westcott used zinc sulfate containing 25 percent metallic zinc. Some growers who reported injury following the Dithane D L4 spray recommendations were using the same amount of 36 percent zinc sulfate. Comparisons of sprays prepared with equal quantities of the 25- and 36-percent material showed that injury resulted from the latter spray under conditions which tended to dry out the flowers. A reduction in the amount of 36 percent zinc sulfate reduced the injury. If the flowers were deficient in water for a longer period, injury was produced by Dithane D-14 sprays containing any concentration of zinc sulfate. A slightly greater water deficiency resulted in injury to unsprayed flowers. Spray injury consisted of burning and drying of the petals from the margins inward. Because large amounts of water are lost through the flowers and injury is severe with low water content, azaleas in flower should be watered during dry periods. Varying the zinc sulfate contents of the sprays had no effect on the control of petal blight. If no zinc sulfate was added, injury also resulted although control was obtained with three applications a week.

Use of dusts was investigated because of the ease of application, particularly in small gardens. Six-percent dusts of zineb (Parzate and Dithane Z-78) gave satisfactory control but were not as effective as the sprays. Use of dusts is recommended for small gardens not equipped to spray.

Applications of a protectant fungicide should begin at the first evidence of the disease usually about the time early varieties (such as Elegans) are in full bloom or when midseason varieties (such as Formosa or Pride of Mobile) are beginning to bloom. Applications may be less frequent when all the flowers have opened and are covered with a fungicide. Spraying should be in the form of a fine mist directly into the flowers, but should not be continued until there is runoff of the material. In a number of show gardens, parks, parkways, estates, and home gardens, one of these control methods is used as a regular procedure.

D. L. GILL is associate pathologist in the Bureau of Plant Industry, Soils, and Agricultural Engineering. He studied at Louisiana State University and Cornell University. From 1935 to 1941 Dr. Gill taught ornamental horticulture at Louisiana State University. He has been with the Department of Agriculture since 1941, conducting research on diseases of azaleas, camellias, and other ornamental plants in Southeastern States. He is stationed at the Georgia Coastal Plain. Experiment Station at Tifton, Ga.

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