Citrus Leaf Pests

Oranges are only one member of the citrus family.

Citrus trees, whether planted in large numbers in an orchard or singly in backyards, always add beauty to the landscape. Citrus trees grow between 6 and 30 feet tall depending on the species. The most common citrus trees in the United States grow in USDA Hardiness Zones 8 through 10. Some hardy citrus trees, like citrange and the Changsha mandarin, can grow in Zone 7 as well.

Pest Identification

Citrus plants can have several pest and disease problems. Some pests cause large amounts of damage to a plant, even though they mostly affect the foliage and not the fruit. Grasshoppers, aphids, and the citrus leafminer all damage citrus leaves. According to the University of Florida, the eastern lubber grasshopper and the American grasshopper cause the most harm to crops. Eastern lubber grasshoppers grow to 2 to 2 1/2 inches long, and are bright yellow with black-and-red markings. Aphids have pear-shaped bodies, and are just under 1/4 inch in size. The adult citrus leafminer moth also only grows to around 1/4 inch long, but it has silvery scales on its front wings that help to identify it.

Pest Life Cycles

Eastern lubber grasshopper eggs lay dormant through the winter and hatch in the spring. The American grasshopper spawns two generations of young every year, and adults survive winter by taking shelter in areas with dense plant growth. Female aphids mature very quickly, and can sometimes lay eggs within five days after hatching. When an aphid infestation grows too large for a plant to sustain, aphids with wings will develop and spread to new plants. Female citrus leafminer moths can lay 30 to 75 eggs in their 11-day life span. Eggs will hatch sometime between day 2 and day 10, and the larva immediately begin to feed.

Damage

Grasshopper damage to citrus leaves occurs primarily due to adolescent nymphs, immature grasshoppers. Nymphs typically feed in the mid- to late morning, and excessive feeding can cause defoliation on young trees. Aphids feed on new growth, which causes the leaves to curl. Curled leaves cannot produce enough energy for the tree. Sooty mold also grows on the excretions of the aphids, known as honeydew. According to the University of Arizona, the citrus leafminer damages citrus leaves during its larva stage. Tiny larva feed on the inside of the leaves, creating small tunnels or mines that give them their name.

Chemical Control

Chemical control of grasshoppers requires 50 to 100 gallons of spray for every acre. Most of the chemical spray should be applied to the bottom 2/3 of the trees' canopy. Along with chemical spray, isolation is also needed to remove aphids. Spray should be used on young foliage before any leaf curling begins. Chemicals used to control citrus leafminers include abamectin, imidacloprid, and spinosad. Research the effects of each chemical before use.

References

• Sunset: Citrus Trees
• University of Florida: Grasshopper, Katydid and Cricket Pests of Florida Citrus: T. R. Fasulo and R. F. Brooks
• University of Arizona: Citrus Leafminer: David Kerns, Glenn Wright, and John Loghry
• University of Florida: Aphid Pests of Florida Citrus: T. R. Fasulo and S. E. Halbert