Aphids: where do they come from and what should we do about them?
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
A few nurseries have reported some problems with aphids on a variety of plants, and some homeowners have already reported aphids, too. Most everybody has seen aphids on roses, peppers or some type of plant. The small (1-2 mm long), soft bodied, green to yellow or black, insects with twin “tail pipes”, usually come in colonies of 10 or more on leaves, stems or shoots of plants. One thing you can be certain of is that there is a kind of aphid capable of feeding on every type of landscape plant. Some of them have complex life cycles, where they feed on tree leaves in the spring, then on the roots of a different type of plant during the summer. Aphids have the advantage of bearing live young, which is unusual for insects. This helps them reproduce very quickly. At an average temperature of 80°F, an aphid can complete one generation in seven to ten days. With each female bearing 40 or more young, you can see how quickly populations can build-up, appearing almost like magic.
Fortunately, we have excellent natural enemies for aphids: parasitic wasps that lay their eggs inside of aphids, ladybird beetles, lacewings, damsel bugs and many others. These predators and parasites keep aphids in check. They are so effective, that under natural conditions we rarely see any problems with aphids. When we see aphid problems on plants, it is usually because an insecticide was applied for some other pest problem, causing a secondary outbreak in aphids weeks or months later.
Long-term management of aphids is simple: avoid using broad spectrum insecticides like pyrethroids, carbamates or organophosphate insecticides. This will allow the natural enemies to return and keep the aphids under control. Restoring natural enemy activity after an insecticide application could take a year or longer. Meanwhile, you may want to use a 1 percent solution of insecticidal soap, or a strong stream of water to dislodge the aphids.
Short-term management of aphids, or the treadmill approach is to spray a pyrethroid insecticide like Talstar, Tempo, DeltaGard, Scimitar, Astro or Asana. This will eliminate the aphid problem for four to eight weeks. After that time, the aphids may come back very quickly, requiring another spray. Many of the products available for homeowners to use in the lawn and garden contain a pyrethroid insecticide. Nurseries and homeowners also have the option of using a systemic nicotinoid insecticide for aphid control. Homeowners can purchase a product containing imidacloprid (Bayer Tree and Shrub Insect Control, and others), while nurseries can purchase Discus, Celero or Flagship to drench around the base of infested plants. The insecticide is absorbed through the roots and should suppress aphids for eight to 12 weeks. Also, you should not see as much of a rebound in aphids after that time, because the systemic nicotinoid insecticides are not as harmful to natural enemies