|Fire blight||Flower clusters are killed and turn dark drown to black. Dead leaves and aborted flower parts remain on the tree. Long, slightly sunken cankers are seen where the dead wood meets the live wood. In the spring, slime may ooze from the canker if the weather is warm and wet. No fungal fruiting structures are found in the canker.||Erwinia amylovora||During dormancy when the weather is dry, prune infected branches, cutting at least 4 inches below the base of the canker. Disinfect pruning tools frequently. Use fertilization practices that do not promote excessive succulent growth. Remove root suckers and water sprouts while they are small. Remove unwanted plants that are susceptible to the disease from near cultivated plants.|
|Cedar-hawthorn rust||Orange-yellow spots form on leaves. Severely affected leaves fall prematurely. Green fruit is deformed.||Gymnosporangium globosum||Plant resistant hawthorns including cockspur thorn, yellow fruited thorn, Crataegus intricata, and Crataegus pruinosa. Apply a fungicide at 10-day intervals beginning just as flower bud break occurs. Do not plant close to junipers.|
|Cedar-quince rust||Petioles, twigs, and thorns swell and become distorted. Fruit is covered with spore horns during the summer. Orange-yellow spots form on leaves, which, if severely affected, fall prematurely.||Gymnosporangium clavipes||Apply a fungicide at 10-day intervals beginning just as flower bud break occurs. Do not plant close to junipers.|
|Leaf blight and fruit rot||Leaves wilt, turn brown, and die in the spring. Flower clusters die. Fruits turn brown, mummify, and fall.||Monilinia johnsonii||Remove and destroy fallen mummified fruits before bud break occurs.|
|Leaf spot||Many small, reddish-brown to gray leaf spots develop, sometimes with dark-brown borders. Spots may be so numerous that they merge. Infected leaves yellow quickly and fall by August. On twigs, slightly raised, brown, irregular spots form. English hawthorn (Crataegus oxycantha) and Pauls Scarlet (Crataegus oxycantha pauli) are very susceptible.||Diplocarpon mespili (Entomosporium, asexual stage)||Rake and destroy fallen leaves. Apply a fungicide during bud break and at 10-day intervals during wet weather. Two or three applications may be sufficient. Cease spraying if the weather dries.|
Cedar rust on fruit, leaves and twigs of hawthorn.
Leaf spot caused by Diplocarpon (Entomosporium).
Fire blight of flowers.
Slightly sunken fire blight canker on larger branch.
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