The distinctive white flowers and shiny green leaves of the lemon tree make it a nice addition to any garden. But like all citrus trees, they can easily attract a variety of insects, including black ants. Understanding why the ants are drawn to the tree is the key to solving the problem.
Ants Follow Aphids
All deciduous trees and shrubs, including lemon trees, attract aphids that feed on the sap. Aphids are tiny green bugs, easily spotted by examining leaves and branches closely. They secrete a sweet substance known as honeydew, which is a favorite food of ants. Clearing the tree of aphids is the only way to permanently stop the black ant infestation.
Simple Aphid Control
There are several simple ways to get the aphids off the tree. Dislodge the aphids using a garden hose with as much pressure as possible and thoroughly spray the leaves and branches. This will dislodge most of the aphids, and they will quickly become food for ground-dwelling insects. Repeat the hosing down as often as needed until the aphids are gone. Another method for small trees is to add a few drops of dish soap to a spray bottle of water. Shake well and spray the undersides of the leaves. The soap will kill them fairly quickly.
Using insecticides to control aphids is not really necessary, because they can easily be eliminated with nontoxic methods. However, if the infestation is severe and persistent, try a natural pesticide such as neem oil or a mild insecticidal soap. As with any pesticide, natural or chemical, be sure to follow the instructions closely to avoid applying too much. Always apply early in the morning or late at night to avoid spraying helpful insects such as bees.
An excellent way to control aphids and stop the ants that follow them is by encouraging beneficial insects to live in your garden. Ladybugs have voracious appetites for aphids and other nuisance insects. If ladybugs are in short supply in your garden, try planting some herbs that will attract them. Cilantro, dill, fennel and yarrow are just a few of the herbs that ladybugs enjoy.
Horticultural glue is another way to keep black ants and other crawling insects off your lemon tree. It is available at most garden centers; one container is usually enough for five to 10 trees. Lemon trees have sensitive bark, so be sure to wrap the trunk before applying the glue. There are several specially made wrapping products available, but even simple masking tape will do the trick. Wrap the tape around the trunk starting about 2 feet off the ground. The tape should be 3 to 4 inches high and covered with a 2- to 3-inch band of glue.