Why are aphids attacking my viburnums year after year even though I spray them?
The spraying is likely part of the problem. Aphids suck sap from the leaves, stems and buds of their victim plants, causing leaves to curl and buds to distort. If the damage is severe, the leaves can drop and your plant then spends the rest of the season looking tragic.
Because of this, gardeners commonly grab for the insecticidal soaps - or worse - synthetic pesticides to control the problem. Often this is unnecessary.
Aphids are the favorite food of several beneficial insects, including aphid midges, lady bugs, green lacewings and parasitic wasps. In spraying, you’re not only killing the bad guys, you’re potentially taking out the good guys as well. And since one surviving aphid is all it takes to reconstitute a colony (aphids can reproduce asexually) once you’ve obliterated their natural enemies, you’ve signed yourself up for a spray program, whether you like it or not.
Instead of spraying, consider investing in plants that produce large amounts of nectar or pollen. They attract beneficial insects who in turn will take care of the aphids before they get out of hand. If impatience gets the better of you, you can hose down your viburnum's stems and leaves with a strong spray of water every morning until the bugs get the message.
I’ve heard of people buying lady bugs and releasing them on or near infested plants to ensure that predator and prey get together. The problem with this approach is that lady bugs a) have wings and b) don’t follow instructions very well. They're just as likely to use those wings to find themselves a tasty colony of aphids three blocks away as they are to stick around in your backyard.
The better idea is to spend your money on a good bug book and learn how to identify the beneficial insects in your garden. Monitoring aphid populations each morning will then become exciting as you begin to notice that predators are doing more than you previously thought to make your life easier.
If you have any questions or comments, please send them to me at vanessa@gardenmuse.ca.
Originally published in the Creston Valley Advance on August 4, 2007.
