The Meyer lemon is actually not a "true" lemon. Imported from China in 1908 by a USDA worker, the Meyer lemon resembles a large orange. A fairly small and thornless tree, this citrus is cultivated as a substitute for real lemons as it is more tolerant to cold temperatures. Because it was prone to the citrus tristeza virus, however, it was banned in the United States until the 1970s brought a new, disease-resistant variety. This new variety can still be plagued by parasites, so it is wise to be sure that you know the signs of parasitic infection on your tree.
Types of Parasites
There are a wide variety of parasites that create problems with Meyer lemon trees. Citrus red mites are small spiders that drink sap from the tree's leaves and fruit, causing the foliage to turn yellow at that spot. Tiny aphids suck the juice out of stems and leaves. They can be very difficult to spot as their grayish-green bodies blend in with the foliage. Thrips are long and range from light orange-yellow to white in color and can be found on or under the tender young leaves and fruit. Scales are very small insects that do not move and that appear as a brownish scaly growth on foliage.
Identifying a Parasitic Infestation
Identifying a parasitic infestation can be difficult since each insect leaves different evidence. Because citrus mites are hard to spot, damage to the plant may be the first hint you have that you have an infestation. Look for yellowed spots, foliage turning bronze and webbing over a significant part of the tree. Silvery, scabby scars on your citrus fruit suggest that your tree may be infested with citrus thrips. Yellowed, dropping leaves and stems that feel sticky often harbor a colony of aphids. The destructive orange dog caterpillar chews leaves and stunts the tree, resulting in small, malformed fruit. Scaly growth accompanied by dying or dropping foliage is a sure sign of scales.
Most of the time trees can survive an infestation if the parasites are removed before the tree sustains too much damage.
While the method for treating parasitic infestations sometimes depends on the type of pest, there are a few things that apply for all. Prune all affected leaves and branches, sterilizing the shears between cuttings to prevent spread. Remove all pruned foliage from the area, either bagging it in plastic bags for disposal or burning it. Spray the tree with a broad-spectrum insecticide, making sure that it is suitable for use in your area and for the type of parasite you are trying to eradicate. Make sure to continue inspecting and treating until the parasites are completely gone. Some pests, like aphids, also respond well to organic, insecticidal soaps and oils, such as neem oil.
Preventing an Infestation
At the beginning of the growing season, spray the entire tree with a broad-spectrum pesticide, repeating treatments periodically throughout the season as directed by the product. Inspect your Meyer lemon tree frequently looking for any signs of damage, and continue to practice good garden hygiene.
Because some of these parasites, such as aphids and thrips, can easily spread to other trees and plants, be absolutely sure to carefully inspect your entire garden, especially nearby young plants that might be particularly susceptible. Sterilize any garden tools or pruning shears after using them on the infected tree by dipping them in a solution of one part common household bleach to nine parts water before using them on any other plant. This will prevent the parasites from transferring from your Meyer lemon to other areas of your garden.