In the Garden with Susan: Aphids in the garden
Aphids are one of a gardener’s most dreaded insects. These tiny bugs use their piercing/sucking mouthparts to extract the sap from both ornamental and vegetable plants.
Within the landscape, some of their favorites are roses, lupines, honeysuckles, maple trees and viburnums. In the vegetable garden, aphids are drawn to artichokes, beans, cabbage family crops (arugula, broccoli, Brussels sprouts, cabbage, cauliflower, kale, kohlrabi, radishes, rutabagas and turnips), corn and peas.
Signs of their damage include discolored, puckered leaves and a clear, sticky residue that they exude from their feeding activities.
The great news is that nearly all predatory insects think aphids are delicious. Examples include assassin bugs, big-eyed bugs, damsel bugs, earwigs, ground beetles, hoverflies, lacewings, ladybugs, minute pirate bugs, parasitic wasps, praying mantids, robber flies, soldier beetles and garden spiders.
There are many ways to control aphids without having to resort to chemical pesticides. These include spraying the aphids off plants with a strong jet of water from your hose or crushing them with your fingers. You can apply an organic product such as horticultural oil, insecticidal soaps, neem oil, plant extracts or pyrethrins. With the exception of plant extracts, the other products are toxic to pollinators. You can still use them; just remember to apply them when pollinators aren’t active, such as very early in the morning or late in the day.
It’s also important to avoid the excessive use of nitrogen fertilizers because they promote the leafy green growth that is a magnet for aphids.
I like to keep things simple by covering my most susceptible crops – primarily those in the cabbage family – with floating row cover as soon as I plant the seeds or seedlings. This lightweight fabric acts as a physical barrier that will keep aphids away from these crops.
You might be interested to hear about an unusual technique for dealing with aphids, which Gabi Tilley brought to my attention. In addition to being the plant sale co-coordinator for The Friends of Manito, she is an avid gardener who loves trying new methods.
“In my garden, I mostly deal with aphids on lupines, columbines, roses and an ornamental hops vine,” she explained. “While listening to a podcast three years ago, I learned that worm castings can be used to control aphids.”
What Tilley found out was that by sprinkling worm castings – an organic soil amendment made from earthworm waste – around the base of susceptible plants, it causes them to produce more of an enzyme called chitinase. When insects feed on the leaves, this enzyme breaks down the chitin (a natural polymer) in the bugs’ exoskeletons, which kills them.
“My hops plant is so big and gets so many aphids every year,” she said. “I bought a bag of worm castings at the garden center, sprinkled a couple of handfuls around its base and watered it in. Within two weeks, there wasn’t a single aphid left on it. I have done this for three years now and haven’t had any aphid problems on the hops.”
“This has been a great solution,” she added. “I’m not out to eradicate every aphid in the yard because I know the beneficial insects need to eat them, but I don’t want a giant mass of aphid stickiness next to my front door.”
North Carolina State University has been conducting research on this topic. It will be interesting to learn more about how this method could help gardeners with particularly challenging insect problems.
Susan Mulvihill is author of “The Vegetable Garden Problem Solver Handbook” and “The Vegetable Garden Pest Handbook.” She can be reached at Susan@SusansintheGarden.com. Watch this week’s video at youtube.com/susansinthegarden.