Springtime in the garden means planting, weeding, watering and keeping a sharp lookout for aphids. Aphids are especially attracted to succulent plant growth, so you need to check your garden frequently when the plants are growing rapidly. Once aphid populations are high and they have begun to distort and curl leaves, it’s often harder to control them because the curled leaves protect the pests from sprays or natural enemies. I’ve seen aphid-curled plum and apple trees already this spring.

Aphids tend to show up first along the upward edges of the garden, or close to other aphid infested plants. Many aphid species infest the undersides of leaves first, so be sure to turn leaves over while you’re checking you garden. On tall trees, you may need to clip off leaves from several areas to look for aphids.

When you find aphids, check for evidence of natural enemies like lady beetles, lacewings, syphid fly larvae and the mummified skins of parasitized aphids. It’s very important to learn to recognize aphid mummies, as they indicate that tiny parasitic wasps have been laying their eggs inside the aphids. The wasp larva hatches and feeds inside the aphid, killing it shortly before pupating. The skin of the dead aphid turns crusty and golden brown or black, a form called a mummy. In a short time the adult wasp chews an exit hole, and emerges from the aphid’s body. The generation time of most parasites is quite short when the weather is warm, so once you begin to see aphid mummies on your plants, the aphid population is likely to decline quickly.

There are also some fungus diseases that infect aphids, especially when it’s warm and humid. Entire populations of aphids may be killed by these diseases when conditions are right. While aphids thrive under mild temperatures, populations of many species are reduced by the hot summer weather conditions in the Central Valley. If you have any of these natural controls at work, it may mean that the aphid population may crash rapidly, so you need to watch it closely.

Check your fruit trees for ants; large numbers of ants climbing up and down tree trunks usually means there are aphids infesting the tree. Ants are attracted to the honeydew produced by the aphids. You may be able to control aphids in your trees by controlling ants. If you plan to use pesticides for ant control, be sure to seek out and treat the ants’ nests in the ground near the tree. Or, you can place sticky barriers around the tree trunk to keep the ants from reaching the aphids. Unprotected by the ants, the aphids may then be attacked by natural enemies.

You can help prevent aphid infestations, especially in vegetables, by removing weeds where aphids may be building up. Also, check your transplants for aphids and remove them before planting. If you notice a few curled leaves on your fruit trees, the best control may be to simply prune out and dispose of the infested shoots and leaves.