Key lime trees (Citrus aurantifolia Swingle) are also known as Mexican or West Indian lime trees. This species has a lower yield than regular lime trees and produces smaller, lighter-colored fruit. The trees are also small and seldom grow taller than 12 feet, which makes them ideal for home gardeners. Few pests target key lime trees except the citrus snow scale. However, key lime trees are vulnerable to the same pests as other citrus trees.
Citrus Snow Scale
Citrus snow scale (Unaspis citri) specifically attacks key lime trees. This scale insect is a kind of aphid also known as orange chionaspis, orange snow scale, white louse, white louse scale and white snow scale. Although not currently present in California, it’s on California’s invasive species list, and there is a moderate risk this pest could come into the state. Citrus snow scales are 1.5 to 2.25 mm long and primarily cause damage to the trunk and large branches. However, it’s also found on the fruit, leaves and twigs. Introducing beneficial parasitic wasps such as Aphytis lingnanensis and Encarsia species helps control outbreaks.
Citrus leafminer, Phyllocnistis citrella, damages the leaves of citrus trees by tunneling between the upper and the lower surfaces of the leaf. During this moth's larval stage, it attacks all kinds of citrus trees and can be found as far north as the San Joaquin Valley. Citrus leafminers target tender young leaves and rarely cause enough damage on mature backyard key lime trees to cause serious harm. Pesticides don’t control the citrus leafminer. Instead, set pheromone traps or release parasitic wasps (Cirrospilus and Pnigalio species).
Citricola scale insects, Coccus psuedomagnoliarum, represent a serious problem for citrus trees in the San Joaquin Valley. A serious citricola scale infestation reduces the size of fruit and significantly reduces yield the following year. Like other scale insects, these pests suck sap from the tree and then exude a sugary substance called honeydew onto the leaves and fruit. Honeydew attracts black sooty mold, which compromises the quality of key lime fruit. Broad-spectrum insecticides, such as organically approved petroleum oil sprays you can get at a garden center, control citricola scale better than biological controls. Inland, avoid applying petroleum oil sprays in temperatures above 95 degrees Fahrenheit or if relative humidity falls to 20 percent or below. If you live in a coastal area, avoid applying petroleum oil sprays if the temperature is higher than 85 degrees Fahrenheit or the relative humidity is below 30 percent.
Citrus Fruittree Leafroller
The citrus fruittree leafroller (Archips argyrospila) is a green caterpillar. These pests are called leafrollers because they form nests by wrapping leaves or blossoms together with silken threads. When the new larvae emerge from the nests, they feed on new growth, which provides entry sites for damaging organisms. If not treated, the fruit drops off the key lime tree within one to two weeks. To control this pest, release the parasitic wasp species Trichogramma or spray with Bacillus thuringiensis, which is acceptable for use in organic orchards.
Your Planting Articles
- California Invasive Species Advisory Committee: Unaspis citri
- University of Texas Cooperative Extension: Home Fruit Production -- Limes
- University of California Statewide Integrated Pest Management Program: Citrus Leafminer
- University of California at Riverside Center for Invasive Species Research: Citricola Scale, Coccus psuedomagnoliarum
- University of California Statewide Integrated Pest Management Program: Citrus Fruittree Leafroller
- University of Florida IFAS Extension: Key Lime Growing in the Florida Home Landscape
- University of California Statewide Integrated Pest Management Program: Citrus -- Precautions for Using Petroleum Oil Sprays
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