How To Identify And Treat Citrus Tree Diseases And Insects

Citrus Tree Diseases

Greasy Spot

Greasy spot is a fungus, known as Mycosphaerella citri, that affects the leaves of citrus trees and thrives in tropical and subtropical climates. The fungus appears as yellow, dark brown, or black lesions that initially occur on the underside of mature citrus leaves. As the fungus develops, the spots become visible on the leaf top. Citrus tree leaves affected by Greasy Spot will fall prematurely, which adversely affects tree health and yield. Once established, citrus Greasy Spot can also infect the fruit and produce rind blotch, more common on grapefruit trees. Collecting and removing fallen leaves can help control Greasy Spot. You can also spray with Liquid Copper Fungicide in June or July, with a second spray application in August or September. This will help protect late summer growth from the onset of the Greasy Spot fungus.


Melanose is a fungal infection of young citrus fruit caused when spores produced by the asexual stage of the disease (Phomopsis citri) grow in dead tree wood and twigs, and then spread to leaves under cool, wet conditions. From there, the fungus can infect young citrus and create blemished fruit. The disease affects grapefruit more readily, but is not limited to grapefruit alone. Melanose is a cosmetic citrus disease that affects the appearance of the fruit, but not the fruit quality or ultimate citrus tree health. The disease is generally more severe in trees over ten years of age. Punctual pruning is an effective way to prevent Melanose, especially when dead twigs and branches are caused from freezing temperatures. Liquid Copper Fungicide spray during temperatures below 94 degrees Fahrenheit can prevent Melanose, but may cause existing blemishes to darken. Strobilurin-containing fungicides are also effective to control Melanose, and can be applied at any time.

Citrus Canker

Citrus Canker is a bacterial infection caused by the pathogen Xanthomonas citri. This pervasive citrus tree disease creates circular lesions, or scabs, on citrus fruit, leaves, and twigs. Newer lesions are yellow, and more mature Citrus Canker lesions become brown. Citrus Canker is highly contagious and can be transmitted by wind-blown rain, or mechanically by pruning equipment, ladders, vehicles, and clothing. Citrus Canker causes necrotic dieback, tree decline, premature fruit drop, and blemished fruit. There are a variety of sprays designed to protect citrus trees from Canker infection, such as Liquid Copper Fungicide as a preventative treatment. However, already infected trees should be removed and destroyed to prevent further contamination from the contagious Citrus Canker disease.

Root Rot

Root Rot (also known as Brown Rot or Collar Rot) is a citrus tree disease caused by the soil-inhabiting fungus, Phytophthora. Root Rot symptoms include dark brown or black patches of hardened bark on the tree trunk, mainly at the base. It is also common for ooze to seep from the affected area. As citrus Root Rot advances, tree bark dries, cracks and dies. The infected area is then left as a dark sunken crater, or indention. As Root Rot progresses, it can cause the fruit to become brown and slowly decay. Leaves may also turn yellow and drop. Root Rot fungus exists in the soil and thrives in wet conditions, such as periods of flooding or excessive rainfall. The disease can then migrate to the tree from splashed or windblown dirt. To prevent citrus tree Root Rot, remove all decaying material such as leaves, dead weeds, and fallen fruit from the ground surrounding the tree base, and prune lower limbs to at least two feet above the ground. Spraying citrus trees including limbs and trunks with fungicide will also control Root Rot.

Sooty Mold

Sooty mold is a black leaf fungus that is the symbiotic result of mold forming on leaves where honeydew secretions from insects like whiteflies, aphids and mealybugs provide the ideal nutrition and harborage for the fungus to grow. Therefore, controlling those insects is the most efficient way to control Sooty Mold on citrus. Spray citrus trees with insecticide formulated to control whiteflies, mealybugs, and aphids, and be sure to spray both the top and undersides of the leaves. To control and eliminate established Sooty Mold, spray the tree with Liquid Copper Fungicide.

Citrus Tree Insects & Pests

Citrus Whitefly

The Citrus Whitefly (Dialeurodes citri) is a small fly that is dependent on new citrus foliage growth for development and reproduction. Citrus Whiteflies feed on the underside of citrus tree leaves, and will take flight in swarms when an infected branch is disturbed. Whitefly larvae create honeydew when sucking sap from leaves, which in turn creates Sooty Mold, and attracts other insects. Several generations of Citrus Whitefly can propagate over a single growing season. Since adults fly, it is difficulty to control an entire Citrus Whitefly population. Therefore, insecticide spraying to control Whitefly juveniles is the most effective means of treating infected citrus trees.


Aphids are tiny insects and nearly all individuals are egg-laying females that produce live young. Males are only needed to produce over-winter capable eggs, so hatching and growing Aphids can create rapid infestations. Because of this, Aphid populations can grow quickly and cause serious damage. Aphid outbreaks are especially fond of succulent new growth. Aphids attack the tree by sucking the sap from leaves. An affected citrus tree will quickly form curled leaves, leaf yellowing, colonies of aphids, and the attendant dripping honeydew will become visible. This can attract ants, as well as Sooty Mold. Eventually leaves will die, and twigs will rot and fall off. Aphids can be controlled using insecticides and insecticidal soap on infected areas, and treating both tops and undersides of leaves, and all branches and twigs.

Citrus Thrips

When a tree is infected with Citrus Thrips the most visible sign of the infestation is curled, enclosed, or shriveled leaves. Citrus Thrips are tiny orange, yellow, or even black insects that can attack trees at any age. Thrips attack young leaves and juvenile fruit and feed on the citrus tree sap. Adult Citrus Thrips lay eggs in the fall and the juvenile insects hatch in spring. To control Citrus Thrips spray the tree with Garden Insect Spray with Spinosad. Repeat spray applications may be required every two weeks. Keep the tree well irrigated and property fertilized, because a vigorous tree is less susceptible, although not immune, to Citrus Thrips.

Orangedog Caterpillars

The Orangedog Caterpillar is a large, brown, green, and white caterpillar about two inches long. The markings create a clever mimic of bird droppings, and an effective deterrent to predators. The Orangedog Caterpillar is the juvenile stage of the black and yellow swallowtail butterfly, common throughout Florida and the tropics. The adult butterfly lays her eggs on new citrus leaves and, as the eggs hatch and new caterpillars emerge, they consume leaf flesh. In sufficient numbers Orangedogs can defoliate an entire tree. To control the Orangedog Caterpillar, physically remove and destroy the caterpillars by hand. When disturbed, the caterpillars may push out two red horn antennas from just behind their head that emit a strong, foul smell. Severe Orangedog Caterpillar infestations can be controlled by spraying with an insecticide that contains either Spinosad, or Bacillus thuringiensis (BTK). Both insecticides are made from naturally occurring bacteria. Spray the entire tree. It is possible that a second spraying may be required in a month or so, depending on the severity of the infestation.


Snails will eat leaves, fruit rinds, and sometimes, citrus tree bark. Snails can be detected visually, or by spotting the damage created as they feed. Snails use leaves on the ground for breeding grounds and as cover. Therefore, to control snails, it is important to remove fallen leaves and fruit from around and under the trees. Also, it is a good idea to prune any low branches that may touch the ground, to keep snails from easily accessing citrus tree interiors. Slug and Snail Bait can be applied to the soil surface to control snail growth and movement.

Brown Soft Scale

Brown Soft Scale is caused by a small insect that attaches itself permanently to citrus tree branches, trunks, leaves, and fruit. Brown Soft Scale insects suck sap from the tree and cause leaves to yellow then drop. Brown Scale also produces honeydew secretion that is conducive to the growth of Sooty Mold.

To control Brown Soft Scale insects, spray horticultural oil to suffocate the scale and eggs. Crawling nymphs only emerge in early summer, so trees can be treated with insecticides at that time to prevent further infestation.

Citrus Bud Mites

Citrus Bud Mite is a tiny, elongated insect that mainly attacks lemon trees located in coastal areas. The lemon blooms are very susceptible because the Citrus Bud Mite attacks the delicate blossom and new leaves, feeding on sap. To control Citrus Bud Mites spray the tree with insecticide such as Bug Buster or Trounce.

Citrus Red Mites

Like Citrus Bud Mites, Red Mites are tiny insects that feed on new growth and sometimes even fruit. The Citrus Bud Mite is red or purple and often inhabits the underside of mature leaves, or the delicate folds of emerging foliage. Severe infestations can cause leaf drop, low yields, and poor tree health. To control Citrus Bud Mites spray trees thoroughly with insecticides such as Bug Buster or Trounce.