Aphids are tiny insects that suck the juices out of your lemon trees, which causes the leaves to wrinkle and turn off color. Although a few of these insects do not cause immediate harm, large infestations eventually stunt the growth of your tree. If you see these bugs or notice a sticky, sooty layer (honeydew) on your leaves, take action to protect your tree. Using a combination of tactics, stop the aphid infestation on your own lemon trees so that they continue to thrive.
Spray water on the tops and undersides of the lemon tree leaves to dislodge aphids on the foliage. Do this in the early morning so that the tree has time to dry during the day. Alternately, if you have a smaller tree, use a Q-tip and rubbing alcohol to remove the sticky areas on the leaves and stems that contain aphid eggs.
Apply a horticultural oil to the tree's leaves in late winter to stop any aphid eggs from hatching.
Spray an insecticidal soap when you spot aphids and be sure to cover the total surface area of the foliage. Allow the spray to dry out before applying water to your tree so that you do not remove this defense.
Introduce beneficial bugs including ladybugs, spiders and parasitic wasps to your yard. Many of these insects are available at garden supply stores.
Monitor your lemon tree and repeat steps 1 to 3 to control the aphid population as needed.