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Citrus Insects & Diseases

Citrus Diseases

Citrus Canker

Citrus canker is a highly contagious bacterial infection of citrus trees causing yellow halo-like lesions or scabs on the fruit, leaves and twigs of citrus trees. Severe infections can cause leaf loss, blemished fruit, fruit drop and die back. The canker bacterium spreads easily and quickly on air currents, insects, birds and on humans by means of clothing and infected implements. There are a variety of sprays designed to protect against infection including using Liquid Copper Fungicide as a preventative treatment, especially when citrus canker has been detected in the area. Unfortunately, already infected trees are generally destroyed quickly to slow down the spread of the bacteria.

Melanose

Melanose is a fungal infection of young citrus fruit, primarily but not exclusively grapefruit. The scabbed fruit rind does not affect fruit quality but it is unsightly. The disease is generally more severe in older trees over 10 years of age. As the fungus propagates in dead wood, prompt pruning is an effective way of combating this disease. Liquid Copper Fungicide say can also be used as a treatment.

Greasy Spot

Greasy spot is another fungus disease of citruses. Telltale signs include yellowish-brownish blister spots on leaves, often on the underside of the leaf. As the disease develops, the spots develop into oily looking blisters. Greasy spot can cause significant leaf loss, particularly during winter and can also infest citrus, particularly grapefruit, rind. To control Greasy Spot, regularly collect and remove any fallen leaves, thus reducing the source of new spores. Spay the tree with Liquid Copper Fungicide in June or July. A second spray application may be needed to be applied in August or September to protect late-summer growth.

Sooty Mold

Sooty mold is a fungus, which causes the blackening of the leaves of citrus trees. The mold forms on the leaves as a result of honeydew secretions from insects such as whiteflies, aphids and mealybugs. Insect control is the most effective way to prevent the incidence of this disease. To control the insects and prevent the secretion of their honeydew discharge, spray the tree with Bug Buster Insecticide. When spraying the tree ensure that both the top and undersides of the leaves are adequately sprayed. A second treatment spray may be required about 10 to 14 days later depending on the severity of the insect infestation.

To control and eliminate the mold growth that has already developed, spray the tree with Liquid Copper Fungicide. Generally one application of Liquid Copper is adequate for sooty mold control, but a second application about 14 days later may be required in major outbreaks.

Root Rot

Root Rot also referred to as Brown Rot or Collar rot is a tree disease caused by the soil-inhabiting fungus from the phytophthora species. Symptoms of this disease are dark brownish patches of harden bark on the trunk of the tree. It is common for ooze to seep from the dark brown infected area. Over time, as the disease advances the bark dries, cracks and dies. The infected area is then left as a dark sunken canker. The disease can also cause browning and decaying on the fruit and yellowing and die-back on the foliage. The disease causing fungus inhabits the soil and is most prevalent in wet soil and during periods of excessive rain. The fungus then attacks the fruit as it is splashed up on the tree by rain or irrigation spraying.

To control for brown rot it is important to remove all leaves and damaged fruit when it falls to the ground; prune of all lower branches off the tree so that the tree branches are more than 2 feet from the ground; spray the tree with a fungicide, when the disease is identified and again the following spring to prevent reinfection. There are two fungicides that can be used to control for the Brown Rot fungus: Agri-Fos and Captan.

Insect Pests

Aphids

Aphids, when in small numbers, do little damage to a tree, however, under favourable conditions the aphid population can grow very rapidly and cause serious damage to a citrus tree during the growing season. The aphids attack the tree by sucking the sap out of the leaves. The symptoms are very visible on the leaves in the form of multiple puckered marks, yellowing and the twisting of the leaves, which gives the appearance of deformed leaves. As the severity of the aphid infestation increases, leaf drop and twig and branch die back can be seen.

Often during an aphid infestation, the leaves appear to be dripping sap from the underside of the leaves. This is actually an excretion from the aphids and is called honeydew. It often drips onto other leaves, other plants and on to the ground. The honeydew then becomes an attractant to ants, which feed on it. In most cases the ants are only symptoms of the honeydew and are not actually attacking or hurting the tree.

Aphids can be controlled using newer and safer insecticides, rather than older more harmful chemicals. For major outbreaks spray the tree with either Bug Buster or Trounce. The spray should be directed at the undersides of the leaves and other areas of visible feeding and insect concentrations. Normally only one or two spray treatments are required to achieve control. For less severe infections or as a preventative treatment, spray the leaves with Insecticidal Soap in the early summer and as needed.

Citrus Whitefly

The citrus whitefly is a tiny white winged insect that is about 1/12 of an inch in length. It is most commonly found feeding on the underside of the tree’s leaves. When the branches are shaken, the Citrus whitefly will rapidly take flight and can be seen fluttering around the tree. In addition to feeding on the citrus tree, the whiteflies also lay their eggs on the underside of the leaves. When the eggs hatch, the juveniles are small oval, almost transparent larva, which attach themselves to the underside of the leaves and begin sucking the sap from the leaves. As a result, the tree’s leaves begin to curl and appear to be covered with a sticky, sooty mold substance.

The mold like substance is actually honeydew that is excreted by the whiteflies because they are not able to metabolize all of the sugars contained in the leaf sap. The honeydew can often be seen dripping from the tree’s leaves and becomes an attractant to other insects such as ants.

Over the growing season, several generations of whiteflies can emerge. To effectively control Citrus Whiteflies spray the tree with Bug Buster or Trounce. It is hard to achieve full control of the adult flies, but several sprayings of the tree with either Trounce or Bug Buster will significantly reduce the juvenile population and in doing so the overall population.

Orangedog Caterpillars

The Orangedog caterpillar is a large caterpillar about 1.5 to 2 inches in length. Its body is a brown color. The caterpillar attaches citrus trees by eating the tree’s leaves. A good indicator that the Orangedog Caterpillar is attacking a tree is leaves throughout the tree appear to be partially eaten or chewed from the outer edges.

The caterpillar is the juvenile stage of the black and yellow swallowtail butterfly that is common in most areas of Florida. The adult butterfly lays her eggs on new citrus leaves and as the eggs hatch and new caterpillars emerge, they can very rapidly defoliate an entire tree in on a few days.

To control the Orangedog caterpillar, physically remove and destroy the caterpillars by hand. It is important to note that the caterpillars when disturbed will push out two red hornlike antennas from just behind their head that emit a strong repugnant smell. If the infestation is intense or physically removing the caterpillars is not possible, the Orangedog caterpillar can be controlled by straying the tree with Garden Insect Spray with Spinosad or BTK Biological Insecticide Bacillus thuringiensis (Bt). Both of these products are safe to use around the home and garden and are made from a naturally occurring bacteria. Be sure to completely spray the tree. With the BTK a second spraying will likely be required in about 7 to 10 days. With the Garden Insect Spray with Spinosad a second spraying may be required in 3 to 4 weeks, depending on the severity of the infestation.

Citrus Thrips

When a tree is infected with Citrus Thrips the most visible sign of the infestation are shrivelled leaf buds and leaves that are curled, distorted and often a silvery grey color. The fruit may be scabbed, streaked or a silvery color.

Citrus thrips are tiny orange or pale yellow insects that attack citrus as well as many other types of fruit trees. They mainly attack young leaves and juvenile fruit and feed on the tree’s sap. The adult thrips lay their eggs in the fall and the juvenile thrips emerge the following spring and begin feeding on the new leaves and fruit. The damage continues throughout the growing season and is most noticeable during hot, dry weather when the tree is already under moisture stress.

To control Citrus Thrips spray the tree with Garden Insect Spray with Spinosad. A few repeat spray applications may be required every 14 to 21 days to achieve full control. Garden Insect Spray with Spinosad is safe to use around the home and garden and is approved for organic gardening. It is also important to keep the tree well irrigated and property fertilized, (see TreeHelp Annual Care kit for Citrus) to help maintain the tree’s vigour.

Brown Soft Scale

Brown soft scale is a common problem on citrus trees, as well as many other types of trees. Soft scale insects are small, non-mobile insects that attached themselves to the wood, foliage and sometimes the fruit. Scale is most common on the new tender woody growth. When adult scale is attached to the tree, it often appears as crusty or waxy bumps on the tree, often it is mistaken for part of the tree’s own growth, but it is actually an insect. The scale sucks sap from the tree and causes the leaves to turn yellow and drop. Often a sticky substance can be found near the scale or on the leaves. This is a secretion from the scale called honeydew and often acts as an attractant for ants or as a growing source for sooty mold.

In the spring or mid-summer, small, almost invisible nymphs emerge from under the female shells and move to infect new areas of the tree. This is the only time in the life cycle of scale that the insect moves.

To effectively control scale insects and limit damage, Horticultural Oil should be sprayed on the tree. The Horticultural oil serves to suffocate the scale and eggs. In the spring or early summer if the crawling nymphs are present, spray the trees with Bug Buster to prevent the new nymphs from further infecting the tree.

Citrus Bud Mite

The citrus bud mite generally attacks lemons, particularly in coastal areas. It is a small-elongated insect with four legs near the mouth and a tapered posterior. As the incidence of this insect peaks in summer, summer and fall lemon blooms are most at risk. The bud mite is difficult to detect but large infestations may be visible by closely examining fruit buttons. To control Citrus Bud Mites spray the tree with Bug Buster or Trounce.

Citrus Red Mites

Like most mites, the citrus red mite is an extremely tiny pest, only 1/50th of an inch long and red or purple in color. These mites infest leaves and fruit. Intense infestations during hot, dry weather can cause leaf drop. To control Citrus Bud Mites spray the tree with Bug Buster or Trounce.

Snails

When snails are present it is common to see holes chewed into leaves and the fruit may be pitted or scarred. You may also see silvery trails winding around the trunk and branches near the soil. Lifting lower branches and inspecting under leaf debris under the tree can also detect snails.

To control for snails, a proper sanitation program around the tree is important. Clean-up and remove all leaf debris under the tree. The leaves on the ground become a good breading and hiding place for snails. Prune and remove any low hanging branches, especially lower braces that may be touching the ground. In addition to a proper sanitation program place Slug and Snail Bait on the ground around the tree trunk. A series of circular rings around the trunk is the most effective placement. Placing a physical barrier on the tree trunk, such as a TreeHelp Bug Band, will also prevent the snails from migrating up the tree trunk and eating the leaves.