June is a beautiful month in the landscape – welcoming peonies, iris, columbine, meadow sage and the inevitable explosion of aphids on perennials, shrubs and trees.
These soft-bodied insects resemble green, tan, red or black sesame seeds and can be found on stems, leaves (often underneath) or flowers. They feast on tender new growth, such as the fresh leaves of the bridal wreath spirea pictured here. Aphids suck sap from plants and in turn, leave behind a sticky, honeydew-like secretion on the foliage.
Depending on the plant, aphids can cause curled leaves, distorted flowers, reduced growth or little to no damage. A black mold may form on the sticky secretion. Ladybugs (or lady beetles) are natural aphid predators and can consume 50-150 aphids a day. The sticky secretion attracts ladybugs and other predators to the desired aphids.
What are options for controlling aphids?
- Let nature take care of it. Ladybugs, green lacewings and other natural enemies can eliminate modest sized aphid invasions.
- Hose off the plant with a strong spray of water directed at the infested area. This is either lethal to the insects or if they survive, most won’t return. Given the size of the aphid population, it can take more than one forceful shower, a few days apart, to be completely effective.
- Prune heavily infested limbs.
- Control with nontoxic insecticidal soaps which are widely available in garden centers.
- If possible, avoid insecticides which also harm beneficial insects.
What about the packaged lady bugs?
It seems like this would be a good idea, but releasing packaged, field collected ladybugs has not been shown to provide long lasting protection. The chance of the “ladies” obediently staying where you want them is questionable. Further, field collected ladybugs can harbor a parasite which is a natural enemy of the ladybug population, according to CSU entomologists.
Want more information?
Check out the following CSU publications:
- Plantalk Colorado, Aphids
- CSU Extension, Aphids on Shade Trees and Ornamentals
- CSU Extension, Lady Beetles
Written by Linda McDonnell, a Denver County Master Gardener