JoAnne Skelly: Do aphids overwinter?

Blooming daffodils and bright yellow forsythia have gardeners thinking about plants and gardens. Along with plants come pests, particularly aphids. Do aphids overwinter? This is an important question, because it influences management strategies. And, the answer is yes.

Aphids are soft-bodied insects that suck plant juices. Since there are over 200 species, most plants have aphid problems at one time or another. They are common on roses, lettuce, fruit trees and ash trees. They suck so much juice out of a plant that they can’t digest it all and exude it as a sticky goo called honeydew. Often, we notice the honeydew prior to the insects themselves, because the goo drips off trees and makes leaves shiny in the sun. It eats the paint off cars and leaves a mess on sidewalks and areas under the trees. Hordes of feeding aphids also make leaves curl up and appear deformed.

Ants climbing trees and shrubs are another good indicator of the presence of aphids. Ants actually “herd” the aphids, harvesting the honeydew.

Aphids are amazing insects. When the weather is warm, they give birth to live young without mating, rather than laying eggs. These young produce more live young, often as many as 12 a day, in one to two weeks, so there are several generations a season. In the fall, they switch to laying eggs, which do survive cold harsh winter conditions. If you had aphid problems on plants, particularly trees, last year, you probably will again.

Dormant oil sprays are one way to kill overwintering eggs. Timing is important. Oils need to be sprayed before buds show color, but as eggs are hatching. Earlier applications will not control aphids according to Dr. Mary Louis Flint of U.C. Davis. Lighter weight oils are available for spring and summer applications. Horticulture oils also work against scale insects. Another management technique is to reduce the amount of nitrogen you apply or use slow-release nitrogen fertilizers. Aphids thrive in a high nitrogen environment.

For lettuce and row crops, protective covers work well, particularly for seedlings. Aluminum foil mulches repel aphids in young plants, but may also repel insect enemies of aphids. Hosing plants off with a strong spray of water also works. Insecticidal soap sprays are another option. Squashing by hand or pruning out aphid-infested plant parts are additional alternatives.

Chemical insecticides are rarely needed for aphid control. Think of them as a last resort.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.