Lemon trees, like other plants, have problems with bugs and diseases which can affect the growth of the plant. Without proper care and in certain environments, the lemon tree can become especially susceptible to bugs. These bugs can drive down the productivity of the plant and even destroy part or all or it. The more knowledgeable you are about the identity of these bugs, the sooner you can eliminate them from your lemon tree.
Aphids are small, green bugs which attack young leaves and shoots in the spring. They suck the sap from the leaves, causing them to distort and curl. A large aphid infestation can stunt the growth of young lemon trees, but most established trees grow right through aphid invasions. Check new growth for aphids and remove them from the plant, as most damage will occur before you even notice if you leave them to feed.
Spider mites and rust mites feed on the fruit and leaves of the plant, leaving brown areas or stripes. Spider mites, which look like little spiders, feed on the leaves in the dry spring and fall months, giving them an etched look. The leaves may then become distorted or drop off the plant. Rust mites are wedged-shaped and appear during the humid summer months. They cause both the leaves and fruit of the lemon tree to turn brown. These pests are small and in order to see them, you may need a magnifying glass.
When young, scale attach to the leaves and stems of the citrus plant. They suck the juices of the plant, causing leaf and fruit drop on the tree. Scale bugs look like small, colored raised spots and if you try to scratch them they will come off the plant easily. If you have a small infestation, simply wipe them off the tree. For large infestations, apply a chemical spray when the immature mites are just born.
Grasshoppers, crickets, katydids and caterpillars sometimes feed on the leaves of the lemon tree and create fruit drop. Caterpillars especially, during summer and early fall, can feed on the leaves of the lemon tree until all the leaves are gone. To eradicate, simply pull the chewing insects off the leaves with your fingers or tweezers.
Citrus leafminers are tiny, light-colored moths whose larvae feed on the young leaves of lemon trees. As they feed, they create meandering tunnels through the leaves that grow larger as the bugs grow larger. This slows the growth of the plant, but will not usually kill it. It can, however, create an opening for diseases such as citrus bacterial canker.
The citrus nematode is a parasite which makes a home in the roots of the lemon tree. The female creates a sort of web in the roots where she lays her eggs. When the eggs hatch, the young nematodes attack the roots for sustenance. This causes the plant to wilt and become generally unresponsive to water and fertilization. The citrus nematode can eventually kill the lemon tree if not treated. Treatment, however, is expensive and your best bet against this pest is prevention.