Infections on the current season's canes result in many instances in shallow white lesions, in some of which the fungus passes the winter and renews growth in the spring to extend the boundaries of the cankers. Some of the tiny white cankers fail to enlarge the following spring; others may remain inactive for another year or two and then become active. Just what determines whether such a lesion is to become active, and when, is not yet known.

Temperature and moisture relations of the brown canker fungus have not received much critical attention. Observations on the fungus outside in early spring and in cultures in the laboratory would indicate that it is active at relatively low temperatures. The pycnidiospores survived for 4 months at 62 F. in a dried culture in the laboratory. Water is necessary for the production, dissemination, and germination of the spores.

The occurrence of brown canker in epidemic severity usually has been associated with injury to the canes. Injuries made by the careless use of the pruning shears or other tools may serve as infection points. When the disease was noted in test gardens of the Department of Agriculture in April 1927, the records indicated that the unusually severe hailstorm of the previous July had been an important factor. The cankers were predominantly located about the wounds produced by the hailstones. Brown canker flourished in gardens in California following the severe winter of 1932-33, when cold weather injured varieties such as the softwooded Golden Emblem; Ville de Paris, Los Angeles, Angele Pernet, Souvenir de Claudius Pernet, and others. Reports from Georgia and other places where extremes of temperature and late spring frosts prevail indicate that injuries from freezing may increase the amount of brown canker.

The overwintering of the fungus in cankers on such roses as R. setigera and R. multiflora that may be growing in nearby hedges or plantings somewhat removed from the rose garden is often an item of importance. Such roses seem to thrive despite the disease and they usually get little attention. The mycelium in the cankers on such hedge plants may be a source of spores for the more formal planting in the garden and make eradication of the disease more difficult.

A control program for brown canker may also help combat the more prevalent but less injurious stem canker caused by Coniothyrium fuckelli and perhaps also brand canker caused by C. wernsdorffiae.

Such a program should include the following: Normally vigorous plants maintained so by attention to drainage, exposure, winter protection, and fertilization; prompt removal and destruction of all dead, dying, and weak parts of plants; systematic spraying and dusting for disease and insect control; care to avoid injury to stems, even small breaks in the epidermis; care in pruning and blossom cutting to avoid leaving stubs, crushing stems, or doing any more damage to the plant than is absolutely necessary; and careful scrutiny of any large, old plants (such as those of R. setigera and R. multiflora), which are back in the shrubbery and may be neglected.

Since wounds serve as infection courts for the canker fungi, it is desirable to handle the plants so as to prevent breaks in the epidermis. Wounds on the rose do not heal quickly. The maintenance of the plants in a vigorous condition may help in the formation of callus. Wounds heal more readily during the early growing season, so there is probably advantage in pruning just before, or just after, growth starts. Care, a pair of sharp shears, and clean cuts immediately above strong eyes will enable one to avoid leaving stubs that so frequently serve as infection courts.

Heavy pruning probably is to be preferred to light pruning insofar as brown canker is concerned. That practice will eliminate many of the initial cankers. Frequent inspection, with the prompt removal and destruction of all ailing plants and plant parts, is advisable if one has a canker problem. A single overlooked canker may supply the spores for general infection through the entire garden.

Regular spraying or dusting, as for black spot or rust control, will assist in canker control in that it will prevent many of the new infections that would otherwise occur. With proper conditions of temperature and moisture, infection can take place directly through uninjured tissue and it is such infection in particular that a fungicide will prevent. But spraying and dusting must be part of a program in which general vigilance and skillful handling are combined with practices making for a clean garden and vigorous growth.

Both copper- and sulfur-containing fungicides are effective in preventing infections by the fungus of brown canker. Maybe the new fungicides effective against black spot will also serve for brown canker. Either spraying or dusting will give protection. Application should begin in the early spring as soon as new growth starts and should be made often enough to provide protection throughout rainy periods and to keep the new growth covered. On the average, an application once a week will be needed from early spring until the plants are dormant.

Frequently the fungus is brought into the garden on infected plants from the nursery. That emphasizes the importance of patronizing reliable nurserymen and of giving new plants a careful examination to be sure they are free from blemishes and infection before being accepted. Particular attention should be given to incipient cankers at the cut made just above the main bud in removing the top of the stock that constitutes the root. Many first-year failures result from infection at this point.

L. M. MASSEY is professor of plant pathology, New York State College of Agriculture, Cornell University. He went to Cornell as a graduate student assistant in plant pathology in 1912 and was granted the doctor's degree in 1916. He served as head of the department of plant pathology at Cornell from 1922 to 1950. He has worked with rose diseases since 1917. Dr. Massey was president of the American Rose Society in 1940 and 1941 and was awarded the Society's Gold Medal in 1947 for invaluable research on rose diseases and distinguished service to the Society.