Table 2. Diagnosis of common citrus problems

Symptom First noticeable Primary cause Occurs Control and/or comments
1. Premature rind coloring late summer plant bugs mid-summer Rarely serious enough to control
2. Creases in rind harvest physiological spring Follow irrigation and fertilization recommendations
3. Necrotic spots on rind, lower part 2 or 3 weeks after spraying spray burn after spraying Excess spray accumulates near bottom of fruit
4. Thick rind, puffy fruit, sheepnose harvest excess vigor since bloom Follow good cultural practices, typical of off-bloom fruit
5. Rust colored or brown rind anytime citrus rust mite since bloom Does not affect eating quality, use miticide only if necessary
6. Silvery to tan irregular, smooth blemishes harvest wind scar March-April Not necessary, quality unaffected
7. Small, brown spots on rind, rough texture, may tearstreak harvest melanose fungus March-April Affects grapefruit only, remove dead twigs inside canopy
8. Removable, small, colored, raised spots on rind summer to harvest scale insects summer Spray only if problem is extensive on the bark
9. Cottony masses near fruit stem summer to harvest mealybug or cottony cushion scale summer Rarely serious, hard to control
10. Black, sooty covering harvest sooty mold since bloom Whiteflies, blackflies, mealybugs and other insects, usually gone before problem is noticed
11. Fruit drop since bloom physiological since bloom Read “Productivity and Maturity” section
12. Fruit splitting on-tree September physiological summer Dry weather followed by good rain, proper irrigation lessens the problem
Leaves and twigs
1. Leaf cupping and curling after new flush aphids during each flush Not serious, check new growth as it emerges
2. Silvery, scratchy appearance to leaf summer, fall spider mites spring to fall Could cause excessive fall leaf drop, spray if necessary
3. Small, brown spots, sand-papery texture spring-summer melanose fungus after growth flush Affects grapefruit, usually after spring rains; remove dead twigs
4. Irregular, oily spots on foliage summer to winter greasy spot fungus summer Remove fallen leaves, particularly in summer
5. Raised, irregular tar-like spots underleaf anytime sunburn anytime Not serious
6. Removable, small, colored spots on leaves or bark anytime scale insects summer Spray only if infestation is extensive
7. Fish-scale-like scales underleaf, translucent; small, white, flying insects spring to fall whiteflies spring to fall Leads to sooty mold; rarely requires control
8. Spirals of eggs or small black insects underleaf anytime blackfly anytime Leads to sooty mold; insecticides do not work, parasites normally in control
9. Black sooty coverings on leaves anytime sooty mold anytime Control causal insects or wash off with soapy water
10. Leaf yellowing, drop and twig dieback anytime root damage anytime Usually too much water, poor drainage
11. Leaf yellowing, tipburn marginal necrosis, drop anytime salt burn anytime Leach soil, be careful with fertilizer
12. Leaf yellowing, yellow area confined to veins anytime foot rot, water damage anytime Determine cause and correct, if possible
13. Marginal necrosis, leaf cupping, curling spring flush wind burn during spring flush Usually not serious, windbreaks may help
Limbs, trunk or entire tree
1. Tree looks sick, sparse, yellow-veined foliage, dead bark on trunk near ground anytime foot rot anytime Remove dead tissues, disinfect and treat with pruning paint; follow recommended cultural practices
2. Hardened gum exudate on bark of trunk or limbs anytime gummosis anytime Follow good cultural practices, no control, not usually life-threatening
3. Young tree seemingly loses all its leaves quickly, fruit hangs on anytime foot rot anytime Check for foot rot (dead bark) completely around trunk at and above the bud union


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