If you have an indoor lemon tree, you probably treasure it for its glossy leaves and bright yellow fruit. But in order to keep your lemon tree healthy, you should monitor it for common insect pests that sometimes attack citrus trees. Insect infestations can be detected in several ways: you may see evidence of the tiny bugs themselves, the sticky residue they produce, or the ants that sometimes accompany them. Shrivelled, curling, browning and falling leaves can also be a tip-off to the presence of insects. If your lemon tree has any of these signs, you should act quickly to control the pests.
Move the lemon tree outside, during mild weather, to expose the tree and its pests to predatory insects that can help decimate their population. According to the Colorado State University Cooperative Extension website, spiders, lady birds and praying mantises are some of the beneficial insects that may approach your lemon tree to feast on the harmful bugs.
Make a non-toxic insecticidal soap solution by mixing 2 tsp of Castile soap to a gallon of water. Douse the lemon tree with it to control the three main pests that affect citrus plants: aphids, scale and spider mites. Leave the soap solution on the tree for three days to give it time to work, then rinse well with water.
Spray the round, waxy bumps that indicate scale infestation with superior-quality horticultural oil to suffocate them, if they persist after the soap treatment. Make sure the spray makes contact with the bumps directly.
Use a spray mister to completely mist the entire lemon tree in order to control any spider mites that may have survived the insecticidal soap treatment. Spider mites, indicated by tiny, pale grey webs on the undersides of leaves, can't tolerate humidity.
Use yellow sticky cards to trap and kill aphids--tiny, tear drop-shaped greenish or brownish insects--on your lemon tree.
Set out ant baits near your lemon tree to kill ants, which actually "farm" scale insects and aphids on lemon trees, moving them from place to place on the plant and then consuming the sticky substance, or honeydew, the bugs produce. If the ants persist, you may need to spray the undersides of your tree's leaves with an insecticide containing pyrethrin, a natural repellent made from chrysanthemums.
Eliminate ant-attracting honeydew by cleaning it off with a cotton swab soaked in rubbing alcohol, then rinsing your lemon tree thoroughly with water.
Read labels carefully if using insecticides, and follow directions exactly. To avoid burning your lemon tree, don't swab it with rubbing alcohol when it is in bright sunlight.