Citrus Tree Pests & Diseases
Like all plants and trees, citrus trees can be affected by disease and insect damage. There are some disease-resistant citrus tree varieties, and they are the best option for preventing many issues. Proper citrus tree maintenance such as watering, pruning, spraying, weeding, and removing fallen fruit can help control most insects and diseases.
Citrus scab is caused by a fungus and it produces slightly raised, pink or brown scabs on fruit and leaves. As the infected areas progress, the scabs will change color to a dark grey, and often crack. The clear oval shaped type of spores are spread by splashing rain and die when they become dry. The spindle-shaped form remain viable for a short time, and in addition to moving with splashed rain, can also travel short distances by wind.
- Raised yellow or pink outgrowths on fruit or leaves
- Small growths on new shoots
Citrus Variegated Chlorosis (CVC)
CVC is a bacterial disease caused by a subspecies of the Xylella fastidiosa bacterium. CVC is transmitted between citrus trees by several species of large leafhopper insects called sharpshooters. The disease can also be transmitted by grafting. Symptoms of CVC are very similar to nutrient deficiency since both result in yellowing of leaves. Early leaf symptoms of CVC closely resemble a deficiency of zinc, with yellowing areas between the veins of young leaves. As infected leaves mature, lesions become visible on the underside of the leaves opposite the yellowing areas on the leaf surface.
- Yellow of young leaf surfaces
- Brown lesions on undersides of mature leaves
Citrus Black Spot
Citrus Black Spot is a disease caused by the fungal infection Guignardia citricarpa. Black Spot can reduce the quantity of fruit produced by a tree, as well as the quality of the fruit. Symptoms include black lesions on both the leaves and the fruit. All varieties of citrus are susceptible to citrus black spot fungus.
- Black spots on mature fruit
- Cracked or oozing black spots in advanced stages
Huanglongbing (HLB) or Greening
HLB, or Greening, is thought to be caused by bacteria carried by psyllid insects. Greening causes leaf discoloration that appears as mottling in various shades of light green to yellow. The leaf discoloration of Greening can be distinguished from nutrition deficiencies because it crosses leaf veins and creates asymmetrical patterns upon the leaf surface. Fruit may also be affected, discolored, and may drop. Greening causes leaves to fall, small new growth to die, the decay of feeder roots, decline of tree health, and eventually tree death.
- Asymmetrical leaf blotches
- Falling leaves
- Fruit drop
- Misshaped or discolored fruit
- Premature and random death of branches
- Removal of infected plants
- Foliar Micronutrient
Citrus Greasy Spot
Greasy Spot is a fungus spread by wind. The fungus thrives when periods of continual wetness saturate decomposing fallen leaves. The fungus will then migrate into trees through splashing rain or wind, and infect living leaves. The symptoms include leaves with yellow spots, raised brownish blisters, and eventually, black lesions that have a greasy appearance.
- Yellow leaf spots
- Brown blisters on leaves
- Black lesions that look greasy
- Foliar Micronutrient
Citrus Anthracnose is a fungal infection that creates round, flat tan spots that have a purple outline. The fungus grows on dead wood in the citrus tree canopy, and can travel short distances by rain splashing or overhead watering, where it can then infect new growth and young fruit.
- Premature stem dieback
- Leaf drop
- Post-harvest fruit decay
- Zinc sulfate, copper sulfate, and hydrated lime
Citrus canker is a bacterial disease caused by the bacterium Xanthomonas axonopodis. Canker creates lesions on leaves, fruit and stems, and can damage overall tree health and fruit production. Citrus canker is spread by wind-driven rain, and can be spread mechanically by transportation of trees, infected limbs, and fruit.
- Yellow lesions on fruit, leaves, and stems
- Brown lesions on undersides of mature leaves.
- Removal and destruction of infected trees
Citrus Leprosis, also called Nailhead Rust, Scaly Bark, or Nailhead Spot, is a virus transmitted by mites that causes lesions that are visible on both sides of the leaf. The lesions are round (ten to thirty millimeters across) and have a dark brown center where mites feed. The Citrus Leprosis virus is carried by the false spider mite (Brevipalpus) and since the virus can multiply within the mites, the mites can spread the virus to trees for the insect’s entire lifespan.
- Small, round dark brown lesions on both leaf sides
- Yellow halo around lesions
Citrus Bacterial Spot
Citrus Bacterial Spot is only known to occur within the nursery environment. There are three classifications of the disease: aggressive, moderately aggressive, and weakly aggressive. Only aggressive isolates are spread by wind-blown rain and overhead irrigation. All other strains can be transported among trees in a nursery by the process of moving vehicles and workers through the nursery grounds. Citrus Bacterial Spot mainly affects leaves, and infections of fruit are rare. It is easily confused with canker.
- Yellow lesions on leaves
- Copper and pruning
Citrus Melanose is an infectiousfungus that lives on dead or decaying plant material. Infections of Melanose are caused when a substantial amount of the fungus is present on dead twigs or branches that are wet for an extended period of time, such as twenty-four hours or more, caused by either rain, or overhead watering. The fungus creates small brown spots on leaves. TheMelanose spots evolve to exude a red-brown gum, and become raised bumps that stand above the surface of the leaf. As the fungus progresses, leaves take on a rough feel due to the numerous bumps. Severe Citrus Melanose infections result in the dieback of young shoots.
- Small brown spots on leaves
- Brownish-red gum on leaves and stems
- Raised bumps on leaves
Citrus Alternaria Brown Spot
Citrus Alternaria Brown Spot is a fungus spread mainly by wind-driven spores. Spores grow on mature, wilted twigs and mature leaves and produce brown lesions on leaves and fruit. Citrus Alternaria Brown Spot can also be transported by the activities of pruning, picking, and transporting trees. Citrus Alternaria Brown Spot can affect the fruit quality as it creates pits, holes, and leaking depressions as the fungus lesions mature on the fruit. Tangerine varieties are particularly susceptible to Citrus Alternaria Brown Spot.
- Brown spots on fruit
- Depressed and leaking spots in advanced stages
- Strobilurin Fungicides
Citrus Phytophthora, also called Root Rot, is a type of mold that thrives in locations of constant moisture and high temperatures. Citrus Phytophthora enters the tree through the roots, and causes small roots and growing root tips to rot and die. Citrus Phytophthora can cause leaves to turn yellow and drop due to the resulting lack of nutrition caused by the damaged roots. Infected trees may also display bark peeling at the trunk base, and a brown to red resin oozing from the tree base. The mold also makes the roots susceptible to damage from root-feeding weevils.
- Peeling lower bark
- Brownish-red resin on trunk
- Leaf yellowing
- Use of resistant rootstock
- Irrigation management
Citrus Pseudocercospora, also known as Phaeoramularia Fruit and Leaf Spot (PFLS) or Angular Leaf Spot, is caused by the fungus Pseudocercospora angolensis. The spores require moisture to propagate and are spread by both wind and mechanical means such as transportation of infected trees or the movement of leaves when pruning and removing branches. The fungus produces flat, light brown to red lesions that have grey centers and mainly affect leaves but can also appear on fruit. The lesionsoften appear amid a field of leaf yellowing.
- Light brown to red lesions with grey centers
- Leaf yellowing
Citrus Psorosis is a citrus disease caused by multiple viruses of the family Ophioviridae. Citrus Psorosis produces an escalating array of symptoms that include yellow spots on leaves, low fruit yields, small circles surrounded by sunken grooves on fruit rinds, and eventually, scale and sticky deposits forming on bark along with deep grooves or pits in trunks and large limbs. The Citrus Psorosis virus may reside in a tree for up to ten years without any noticeable symptoms. The disease is largely transferred through bud grafts, and as such, has been greatly controlled through the application of industry bud material inspection and certification programs.
- Yellow spots or irregular blotches on leaves
- Circles with sunken grooves on rind
- Deeply grooved trunks or pitted branches
- Prevented by proper budwood certification
- Severely infected, older trees removed and destroyed
Sweet Orange Scab
Sweet Orange Scab is a fungal infection of citrus fruits caused by the fungus Elsinoe australis. The fungus affects the appearance of mostly fruit rinds, and less often, young twigs and leaves. The disease does not affect the quality or taste of the fruit, but may cause some fruit to drop prematurely, particularly on younger trees. The spores require moisture to reproduce and are often spread during rain.
- Unattractive scab-like outgrowths on fruit rind exterior
- Sometimes similar scabs appear on twigs and leaves
- Copper Spray
Citrus Tristeza, also known as Quick Decline or QD, is a virus carried and delivered to citrus trees by aphids. Aphids such as the brown citrus aphid contract the virus when feeding on a QD infected citrus tree. The Citrus Tristeza virus can also be spread or, in effect, multiplied through the process of grafting stock for new trees. Many strains of the Citrus Tristeza virus exist, and their effects range from slight, ineffectual damage to rapid decline of tree health and a resulting death.
- Cupping of leaves
- Leaf vein corking
- Leaf flecking
- Pitting of stems
- Deep pitting of trunk
- Treatment and control of Aphids
- Careful inspection for QD symptoms when grafting