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PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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  MG Manual Reference
Ch. 4, pp. 21 - 22
[ Diagnostic Key: vegetables | specific vegetables; asparagus, bean, beet, carrot, cole crops, corn, cucurbits, eggplant, lettuce, onion, pea, pepper, potato, tomato | tree fruits| specific fruits; apple, stone, citrus | ornamentals | specific ornamentals; rose family, rose, palm, pine ]


KEYS TO PROBLEMS ON SPECIFIC FRUIT TREES

APPLE & PEAR Top

SYMPTOMS CAUSES CONTROLS
Black, sooty growth on leaves, stems, and/or fruit • Sooty mold (fungus that grows on honeydew substance secreted by aphids and other insects) • Identify insect then control as needed
Branch dieback; leaves may turn color early in fall; canker present at or below soil level on trunk • Crown rot (fungal disease) • Avoid areas with poor drainage; use registered fungicide; select resistant rootstocks
Bark on young branches is rough and pimpled; tissue beneath bark has brown spots • Measles, believed to be a nutrient imbalance • Amend soil as needed
Leaves wilt, curl, and cling to twigs; shoot tip may be curved into "shepherd's crook"; sunken, black or wine-colored cankers may be present on branches or trunk • Fire blight (bacterial disease) • Prune out and destroy affected branches; remove young suckers as they appear; plant resistant varieties
Pink-white worms bore into blossom end of apple; clusters of round, brown frass pellets inside fruit • Codling moth • Use registered insecticide as indicated by pheromone traps or degree days; clean up fallen fruit; wrap tree trunk with corrugated cardboard and destroy larvae as needed
White cottony masses found on suckers, trunk, and branch crotches; trees may show decline • Wooly apple aphid • There is no control for the below-ground stage of this root aphid; spray branches with hard stream of soapy water
Leaves skeletonized; common on pear; also found on cherry, plum, quince, and apple • Pear sawfly • Apply diatomaceous earth to foliage
Tree breaks off at graft union during strong winds • Poorly constructed graft • Purchase young transplants from reliable dealer
• Virus infection of graft union • Note that some of these viruses are transmitted by nematodes in the soil
Spots form on fruit under the skin; later, in storage, turn brown • Bitter pit, a physiological disease, caused by reduced uptake of calcium and fluctuating amounts of water • Maintain regular irrigation; rapidly growing young trees often show this symptom; the problem decreases with tree age

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