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PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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  MG Manual Reference
Ch. 4, pp. 23 - 24
[ 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

STONE FRUITS Top

SYMPTOMS CAUSES CONTROLS
Swellings and abnormal growths present on roots and/or trunk at or just below ground level; trees appear stunted and lack vigor • Crown gall (bacterial disease) • Chemical controls have not been effective; if this disease has been a problem in the past, replant with resistant species
Purple spots appear on upper surfaces of cherry leaves; leaves develop holes and turn yellow; fruit may also be spotted • Cherry leaf spot (fungal disease) • Resistant cherry varieties include Meteor and Northstar; use registered fungicide spray
• Shothole fungus • Use registered fungicide spray
Gum oozes from holes at base of trunk or lower branch crotches; sawdust may be evident • Peach tree borer • Use paradichlorobenzene (moth) crystals around base of tree; use registered insecticide on bark only; monitor with pheromone traps
Blossoms and young twigs wilt and decay during bloom; sunken cankers may develop on twigs; circular brown spots which develop tufts of gray spores during moist weather form on fruit • Brown rot (fungal disease) • Remove all affected fruit on tree and on ground; prune out any twig cankers
Many small round holes in twigs and branches • Shothole borer • Remove and destroy all dead or dying wood
Sunken, distorted areas on fruit, cat-facing • Various plant bugs • Control weeds and brushy areas around fruit trees

CITRUS Top

SYMPTOMS CAUSES CONTROLS
Poor fruit development (small number of fruit on tree) • Biennial bearing • Older citrus trees tend to become alternate bearers
• Frost injury • Frost recovery triggers more vegetative growth and less fruit
Young leaves curled and distorted; clusters of insects on undersides of leaves • Thrips • Does only cosmetic damage; no control needed
Fruits splitting in the fall • Heat, water stress
• Sun
• Heat, water stress
Peeling bark and gumming near soil line • Fungal disease • Pull soil away from trunk; keep water from touching trunk; clean off the infected bark and treat with Bordeaux as a paste
Gumming up the trunk or on major branches of grapefruit • Rio Grande gummosis • Not a disease, simply a symptom of old age on grapefruit; no treatment needed
Fruits with single small hole; the fruits filled with beetles and flies • Bird damage • Scare birds away or use netting; neither is too effective; the insects are a secondary problem
Navel oranges black at the flower end and down the core Alternaria (fungal disease) • No control; disease is worse during certain weather conditions
Few fruits on navel orange • Heat stress • Navels are extremely sensitive to heat and at first heat of summer most of the fruits may fall off

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