Cypress Canker Control with Fungicides

Cypress canker caused by Seiridium cardinale was controlled by benomyl and chlorothalonil but not by tribasic copper sulfate. Cypress canker has been present in California since 1927 where it has caused considerable damage to planted Monterey cypress, Cupressus macrocarpa (6). The popularity of this California native range and usually canker disease appears, but some uninformed people still plant it out of its native rane and usually canker disease appears, detracting from the beauty of the tree or weakening the tree to the extent that it dies. The disease can be equally severe on X Cupressocyparis leylandii (unpublished observation). The fungal pathogen, originally named Coryneum cardinale, is now known as Seiridium cardinale (5). Wagener and Dimock (8) recommended spraying bordeaux mixture shortly after the start of the rainy season and an additional spray during the winter or early spring. They also suggested painting a thin bordeaux on wounds. Govi et al (1) evaluated nine fungicides for control of the disease on C. sempervirens. Benomyl and dichlofluanid were the most effective and other products including bordeaux and copper oxychloride gave good results. Parrini et al (4) found that benomyl, thiophanate-methyl, oxycarboxin, thiram, dichlofluanid and captan reduced infection; benomyl and thiophanate-methyl were the most effective fungicides evaluated. None of the fungicides evaluated by Govi and Tunioli (2) had any curative activity; benomyl and dodine provided the best protective control. In 1980 Marchetti and D'Aulerio (3) reported that copper oxychloride and benomyl proved to be the most effective fungicides, while carbendazim and fenarimol gave poorer results. With the exception of the Wagener and Dimock (8) research, the fungicide trials have been on C. sempervirens. The purpose of the research reported here was to determine the most effective fungicides for use in managing the disease on C. macrocarpa and C. leylandii. Materials and Methods Conidia were produced on propyleneoxidesterilized needles of Sequoia sempervirens imbedded in 1.5% water agar in petri dishes. Conidia were washed from the plates and adjusted to give 1 X 10/ml. Fungicides were incorporated into melted potato-dextrose-agar (PDA). One ml of conidial suspension was applied to the surface of the hardened agar in 9 cm plastic petri dishes. Germination counts were made 24 hr following inoculation. Circular discs 4 mm in diameter cut from 10-day-old PDA plates were placed in the center of 9 cm plastic petri dishes containing solidified PDA in which the fungicides were incorporated. The diameter of growth was measured 10 days later. Incubation of all plates was in a fluorescent lighted laboratory where the temperature varied from 21-22 C. Cypress trees were grown in a sand-peat potting mixture in 20 X 22 cm plastic containers. Greenhouse-grown plants were fertilized daily with the irrigation water and the plants grown outof-doors were fertilized using 14-14-14 slow release fertilizer. Plants were 70 to 90 cm high when sprayed and inoculated. Trees were wounded in the main stem by making ten incisions 1.0 to 1.5 cm long in the stem extending into the xylem. After wounding, 5 plants for each treatment were sprayed to run off with the fungicides. Chlorothalonil was applied at 1.35 g/liter, benomyl at 0.3 g/liter and tribasic copper sulfate (53% Cu) at 6.0 g/liter. The control trees were sprayed with water. In the first trial conducted in February 1981 with C. leylandii, wounds were inoculated by spraying a conidial suspension 24 hours after fungicide application. The trees were out-of-doors and were covered with polyethylene bags for 48 hours following inoculation. Disease evaluations were made in May, 90 days following inoculation. The second trial was initiated in September Journal of Arboriculture 10(7): July 1984 213 1982 in the greenhouse where the temperatures ranged from 20 to 26 C. C. macrocarpa trees were wounded as before and the same three fungicides were sprayed following wounding. The sprays dried in one hour and the wounds were then inoculated as before. The plants were covered with polyethylene bags for 48 hours. Disease evaluations were made 77 days after inoculation.