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Citrus canker on FoliageCitrus canker is a highly infectious bacterial disease that was introduced to Florida from Japan in 1912. Small round lesions surrounded by a yellow halo are found on leaves and fruit. It is easily spread by insects, birds, people or equipment. There is no cure and infected trees are usually destroyed. - Greening or huaglongbing, was first reported in southern China in 1919 and confirmed in Florida in 2005. Transmission is by the Asian citrus psyllid insect. Adults have a brown mottled body and are 3 to 4 mm long. They can be found on the undersides of leaves. The disease can also be spread through grafting. The most common symptom is blotchy, yellow mottled leaves.The mottling develops in random patterns that can appear on only one side of the leaf. Fruit may be lopsided. Citrus greening is easily misdiagnosed as a nutrient deficiency. Remove infected trees and control psyllids with a broad spectrum insecticide. Trees should not be sprayed while bees are present. Infected trees should be removed.
- Melanose is a fungus disease that primarily, but not exclusively, attacks grapefruit. The scabbed fruit rind does not affect fruit quality. The fungus propagates on dead wood and infects older trees more severely. Control of the disease is by pruning dead wood. Treat trees with a fungicide.
- Greasy spot is a fungus that can be diagnosed by the appearance of yellowish brown blister spots often found on the undersides of leaves. Spray trees with a liquid copper fungicide in June or July. To help prevent the spread of the fungus, remove fallen leaves and destroy them.
- Sooty mold causes a blackening of citrus leaves. The mold develops with the help of the honeydew secretions of insects such as aphids, whiteflies, and mealy bugs. Spray the trees with liquid copper fungicide to control the fungus and an insecticide to control the insects.
- Alternaria produces brown spots surrounded by a yellow halo on fruit, leaves and twigs. Control is by choosing disease-free stock. Overwatering and excessive use of nitrogen fertilizers favor its spread. Spray trees with a copper fungicide, especially during periods of wet weather.
- Citrus scab appears as pale orange, raised warts on leaves. Badly infected leaves become distorted. On twigs and fruit, a similar corky growth develops. The fungus spores develop and spread during periods of warm, wet weather. Spray with a copper fungicide.
