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Diagnosing Dooryard Citrus Problems1
Larry K. Jackson2Citrus is grown in many areas of Florida and in most situations can be cultivated with only routine care. However, the Florida climate is conducive to many different insects, diseases and other disorders in the dooryard situation where many different types of plants are grown in close proximity may promote certain problems. Diagnosis of the many problems which can afflict citrus is often difficult, so this publication has been prepared to assist dooryard growers with this task. The various problems have been separated by where they may be located - the fruit (Table 1 ), the leaves (Table 2 ), or other portions of the tree (Table 3 ). Then, a general description is given and brief suggestions for control are provided. More accurate diagnosis can be made when fresh specimens of the problem can be taken to local IFAS County Extension offices or to local garden supply centers.
Many of the problems are non-pest and spraying is not warranted. Even certain pest problems can be dealt with biologically and sprays are often unnecessary. If chemical control measures are warranted it is important to follow label instructions explicitly to prevent harm to the applicator, the tree or the environment.
Tables
Table 1.
Table 1. Problems of Fruit. Usual Cause When Usually Noticed When Usually Occurred Control Symptom: Fruit drops prematurely Physiological disorder or disease. Various causes. Most acute at bloom, during June, and near harvest. Throughout season Follow recommended cultural practices. Comment: Some early drop is normal since trees often over-bear. Premature fruit drop (PFD) disease may sometimes affect very young fruit, resulting in drop with calyx remaining on stem. Symptom: Fruit is rusty or brown with smooth texture. Citrus rust mite When fruit sizes and begins to mature. Usually during fruit development. Check for rust mites and spray if needed. Comment: Primarily a cosmetic problem. Symptom: Splitting of fruit Physiological disorder Prior to and during harvest season. Just prior to fruit maturity. Avoid water stress, follow fertilizer recommendations. Comment: Not reversible. Follow recommended practices next season. Symptom: Smooth brown or tan irregular blemishes on peel. Mechanical damage from abrasion. Near harvest Usually when fruit is small. No control available. Comment: A cosmetic problem Symptom: Black, smutty covering of fruit Sooty mold fungus Prior to and during harvest. Summer Control insects which cause problem. Comment: The fungus grows on exudates from scales, whiteflies and aphids. Symptom: Granulation, drying of juice sacs. Physiological disorder At harvest Near harvest Regular irrigation. Good cultural practices. Comment: Problem is worse on young or vigorous trees. Symptom: Thick peel Physiological disorder At harvest Near harvest Follow good cultural practices. Comment: Worse on trees which are young or overfertilized, recently pruned. Symptom: Raised scabby bumps on fruit Citrus scab fungus Anytime fruit is on tree Shortly after bloom Preventive spray program Comment: Affects only certain varieties Symptom: Brown, pinhead-sized raised lesions on fruit about 1/16" diameter. Melanose fungus Summer till fruit harvest. Late spring Preventive spray program. Remove dead wood. Comment: Sprays will not reverse damage, must be prevented. Symptom: Grapefruit rind pitting Greasy spot fungus At or near harvest Summer Preventive spray program. Comment: A cosmetic problem Symptom: Raised specks or spots of various colors, usually less than 1/10", removable. Scale insects (there are many types). Anytime Summer, fall Spray if population warrants control. Comment: High populations affect tree vigor. Symptom: Premature coloring, black decay in fruit core. Black rot fungus Late fall Early fall Remove affected fruit. Comment: An infrequent problem Symptom: Premature coloring, very small puncture wounds, some fruit drop. Plant/stink bug injury Late summer, early fall Late summer, early fall Watch for insects and spray if necessary. Comment: An infrequent problem Symptom: Tan, leathery decay with foul odor. Brown rot fungus Near harvest and postharvest Just prior to harvest Preventive spray may be helpful if problem is recurrent. Comment: An infrequent problem. Spray will not reverse existing damage. Symptom: Crease-like, depressed lines in fruit peel. Physiological disorder (creasing). Prior to or during harvest Summer Follow good cultural practices. Comment: An occasional problem of certain varieties. Symptom: Discolored, often necrotic sunken areas of damage to peel. Chemical burn Anytime Anytime Usually results from improper spray rates or application. Comment: Sprays must be applied properly observing all label instructions. Symptom: White, cottony masses usually located around stem. Mealybugs or cottony-cushion scale insects. Anytime Summer Spray should be applied if population warrants. Comment: Only an occasional problem. High population may cause fruit drop. Symptom: Black, raised bumps on fruit stem about 1/8" diameter. Black scale insects Near harvest Late spring Spray should be applied if population warrants. Comment: High populations can cause fruit drop. Symptom: Holes in fruit of various sizes, depths. Chewing insects, birds or rodents. Near harvest Near harvest Observe to determine cause of problem. Comment: Control measures will depend on nature of problem.
Table 2. Problems of Leaves and Twigs. Usual Cause When Usually Noticed When Usually Occurred Control Symptoms: Black, soot-like covering on leaves. Sooty mold fungus Anytime Mainly spring, summer Need to control pests which cause problem. Comment: The fungus grows on exudates of scales, whiteflies & aphids. Symptom: Distortion, curling and/or cupping of leaves. Aphids and/or citrus leafminer Anytime Mainly spring, summer when leaves were tender Control insects on plant. Cannot reverse damage. Comment: Controlling insects will prevent the problem but will not repair existing damage. Symptom: Scratched, silvery appearance to leaves. Spider mites, usually citrus red mite Anytime Mainly spring, fall Control spider mites. Comment: May cause leaf drop in fall with severe infestations. Symptom: Leaves cut, chewed or notched. Chewing insects such as grasshoppers, crickets, weevils. Anytime Anytime but usually during warmer months Difficult- probably best removed by hand Comment: Usually not a serious problem. Symptom: Leaves distorted, often with bumpy, scabby lesions. Scab fungus Anytime During spring growth flush period. Requires well-timed sprays or use resistant varieties. Comment: Must be prevented, spray will not correct. May be on fruit, twigs also. Symptom: Dark brown pinhead-sized pustules with sandpaper texture on leaf surface. Melanose fungus Anytime Late spring - early summer Preventive spray program. Remove dead wood. Comment: Sprays will not correct. May attack fruit & twigs also. Symptom: Dark tar-like spots on leaves usually less than 1/8" in diameter. Greasy spot fungus Anytime Summer Preventive spray program. Remove fallen leaves under tree. Comment: Sprays will prevent, not correct exiting problem. Severe cases will defoliate. Symptom: Raised specks or spots of various colors usually less than 1/10", removable. Scale insects (there are many types). Anytime Summer, fall Spray when population warrants control. Comment: High populations affect tree vigor. May also attack fruit, twigs. Symptom: White, cottony masses on leaves, twigs, fruit. Mealybugs or Cottony-cushion scale insects. Anytime Spring, summer Hand removal or spray if warranted. Comment: Usually not serious except on small plants but may cause fruit drops. Symptom: Small (1/16") translucent discs under leaves with white flying insects present. Whiteflies Summer Late spring, summer Spray if population warrants control. Comment: Sooty mold may be more of a problem than whiteflies. Symptom: Leaf necrosis at tip or margin. Maybe some drop, twig death. Salt accumulation from water or fertilizer. Anytime Anytime Check water supply, reduce fertilizer. Comment: Irrigate with fresh water to leach salts from roots. Symptom: Red or yellow raised spots about 1/12" on underside of leaves. Aschersonia friendly fungus which attacks whiteflies. Anytime Summer Do not control as this is a friendly fungus. Comment: This fungus attacks the immature whitefly. Symptom: Leaf drop, often followed by twig dieback. Root damage, most often due to flooding. Anytime Anytime Avoid excess water. Comment: If flooding has occurred, tree may need to be removed, replaced. Symptom: Pale green leaves, often undersized. Fertilizer deficiency, possible root damage. Anytime Anytime Follow fertilizer recommendations. Check for root, trunk damage. Comment: Check trunk near soil line for fungus lesions. Symptom: Pale green leaves with darker green veins. Nutrient deficiency -- usually microelements. Anytime Anytime Nutritional spray needed. Comment: Follow fertilizer and nutritional spray recommendations carefully. Symptom: Leaf yellowing, necrosis, some leaf drop. Spray Burn--May be salt or chemical Anytime Anytime Wash off excessive residues. Avoid excess rates of spray. Comment: Salt spray is often a problem near the ocean.
Table 3. Problems of Limbs, Trunk or Entire Tree. Usual Cause When Usually Noticed When Usually Occurred Control Symptom: White, snow-like specks on bark of limbs, trunk. Citrus snow scale Anytime Anytime Remove mechanically or use chemical sprays. Comment: Severe infestations may cause limb loss, fruit drop. Symptom: Tree declines, small yellowish leaves, bark lesions near soil often present. Foot rot fungus Anytime Anytime Remove any organic material near trunk, disinfect area. Comment: Cure will be difficult. May need to contact Extension office or local nursery. Symptom: Tree declines without outward obvious symptoms. Blight, virus disease, nematodes, or weevils. Anytime Anytime No control available for these problems. Comment: Diagnosis of actual problem will likely be difficult. Local Extension office may be able to help.
Footnotes
1. This document is Fact Sheet HS-34A, a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised: May 1992. Reviewed: January 1994. Revised: September 1995.2. Larry K. Jackson, emeritus professor, Horticultural Sciences Department, Citrus Research and Education Center (CREC), Lake Alfred, FL, a branch campus of the University of Florida, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
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