There are very few lemon tree problems that are life-threatening. Lemons trees are afflicted with the same diseases and pests as other citrus trees.
If you recognize the symptoms of the most common problems you can take the corrective actions to minimize their negative impact on your lemon tree’s fruit quality. Trees should be examined frequently for pests, diseases, and disorders.
It is very easy to bruise the peel of the fruit on a lemon tree. Releasing peel oil causes serious oil spots on the lemon’s surface. Oil spotting can shorten the life of the fruit. To prevent oil spotting, delay picking fruit until late morning or afternoon, after rain or when the fruit is wet and handle the fruit gently to avoid bruising.
Common Lemon Tree Diseases
Citrus tristeza: The virus, citrus tristeza, causes seedling yellow, severe stem pitting, or quick decline on rootstock and results in reduced crops or loss of trees. It is generally spread by aphids, and when it was discovered that ‘Meyer’ lemons were asymptomatic hosts for this aggressive virus, many growers were told to destroy their trees to prevent large scale infection of commercial crops. The ‘Improved Meyer’ strain is disease resistant.
Asian citrus leafminer: attacks the new flushes of growth and causes stunting and distortion of the leaf. Each growth flush is vulnerable to attack.
Young Tree Decline: symptoms include dead wood, sparse foliage and reduced growth. Affected trees will wilt sooner during a dry spell than healthy trees. A certain amount of dead wood is natural in the normal development of a citrus tree.
Citrus greening: causes infected trees to yellow and decline. Fruit can develop a lopsided shape if trees are infected with citrus greening.
Citrus canker: a highly contagious bacterial infection of citrus trees causing yellow halo-like lesions or scabs on the leaves, fruit and twigs of citrus trees. Severe infections can cause blemished fruit, leaf loss, fruit drop and die back.
Root Rot: also referred to as Brown Rot. The 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 disease can also cause decaying and browning on the fruit and also die-back and yellowing on the foliage.
Greasy spot: a fungus disease of citruses. Telltale symptoms include yellowish-brownish blister spots on leaves, often on the underside of the leaf. As the disease progresses, the spots will develop into oily looking blisters
Sooty mold: a fungus that causes blackening of the leaves of citrus trees.
Disease-like Insect Infestations
Aphids: can be light grey-green, green-yellow, black or brown. Symptoms are easily detectable on the leaves and include the appearance of multiple puckered marks and yellowing and twisting of the leaves. Aphids cause the leaves of lemon trees to appear deformed.
The citrus whitefly: This is an insect that 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. The tree’s leaves begin to curl and appear to be covered with a sticky, sooty mold substance.
The Orangedog Caterpillar: a large caterpillar about 1.5 to 2 inches in length. Its body is a brown color. An easily observed symptom that the Orangedog Caterpillar has infested a tree is the leaves throughout the tree appear to be partially eaten or chewed from the outer edges.
Citrus Thrips: The most visible sign of infestation are leaves that are distorted, shriveled, curled and usually a silver grey color. The fruit may be streaked, scabbed or a silvery color. The damage continues throughout the growing season and is most noticeable during hot, dry weather when the tree is already under stress.
Brown soft scale: These are small, non-mobile insects that attach themselves to the wood, foliage and sometimes the fruit. Scale is most common on the new woody growth. When adult scale is attached to the tree, it often appears as waxy or crusty bumps on the tree. It is often 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.
Citrus bud mite: a small-elongated insect with a tapered posterior and four legs near the mouth. The bud mite is difficult to detect but large infestations may be visible by closely examining fruit buttons.
Citrus red mite: 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.
Snails: chew holes into leaves and cause the fruit to be scarred or pitted. You can also see silvery trails winding around the trunk and branches near the soil. You can also detect snails by lifting the lower branches or inspecting under the leaf debris under the tree.
Photo by Darwin Bell, Creative Commons Attribution License