The sunny weather, blooming daffodils and bright yellow forsythia have gardeners thinking about plants and gardens. My friend Woods recently asked me "Do aphids overwinter?" This is a great question because it influences what is done to control them.
Aphids are soft-bodied insects that suck plant juices. Since there are more than 200 species, many 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 are better able to survive cold harsh winter conditions. If you had aphid problems on trees last year, you probably will again.
Dormant oil sprays are one way to kill overwintering eggs. 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 the University of California-Davis. Lighter-weight oils are available for spring and summer applications. Horticulture oils also work against scale insects. A simpler management technique is to reduce the amount of nitrogen you use or use slow-release nitrogen fertilizers. Aphids thrive in a high nitrogen environment.
For lettuce and row crops, protective covers work, 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 water spray works well. Insecticidal soap sprays are another option. Handpicking or pruning out aphid-infested plant parts is another option.
Chemical insecticides are rarely needed for aphid control. Think of them as a last resort.
- JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension. For information, contact Skelly, at 887-2252 or firstname.lastname@example.org, your local University of Nevada Cooperative Extension office or at www.unce.unr.edu. Ask a Master Gardener at mastergardeners