By Lisa Southworth Originally published March 17, 2016
When insect pests attack prized plants, pesticide-pulling trigger fingers can gobsmack even the most granola among us.
In her 48 years of gardening, Sharon Collman says she hasn’t had to use a pesticide. How does she encourage a naturally balanced, eco-friendly garden?
Simply by leveraging Mother Nature’s awesome arsenal: beneficial bugs, bacteria and brainy plants.
“People often take action much sooner than they need to,” said Collman, a pest management and horticulture educator at Washington State University’s Snohomish County Extension Program.
“When people see a few aphids, they get pretty bent out of shape,” she said. “But if you get your garden balanced out, you won’t see excessive numbers.”
Nature is about balance. If garden pests are present, predators lurk.
More gardeners are turning to this army of natural-born killers: beneficial insects that live to eat what’s bugging plants.
These good guys include ladybugs, praying mantis, beneficial nematodes and even parasitic wasps.
But—there’s always a “but”—making your yard hospitable to beneficial bugs means allowing their food sources, like aphids, worms and grubs, to live.
“When people say to me, ‘I’ve got aphids on my roses, what should I do?’ ” Collman said. “I say to grab a cup of coffee and watch. Watch for the lady beetles looking for aphids. Watch for lacewing adults and larvae.
“Just relax and enjoy the garden, and take action when needed.”
Establish your yard as a beneficial bug haven starting with the origin of plant health—great soil. Grab a shovel and give your soil a turn, so it’s loose and oxygenated, giving roots room to breathe.
Then, have your garden’s soil tested and analyzed. She recommends routine soil analyses from either the University of Massachusetts ($20), or Simply Soil Testing USA, based locally in Burlington ($16).
This step yields priceless results and helps gardeners tailor fertilizer applications.
“Over-fertilizing pushes lush new growth, and there’s nothing an aphid loves more than fresh new growth,” Collman said.
With fluffy, balanced soil, the next step is giving your plants the best start. Put the right plant in the right place to reduce plant stress. So shade plants in shade, sun plants in sun.
That step seems simple, but even our expert has made her share of mistakes.
“Not watering, overwatering, putting something in the wrong spot—I’ve killed way more plants than any insect ever did,” Collman said.
Plants are like people, in that stress creates vulnerability. Plants living in suboptimal conditions become prone to disease or insect infestation.
“I had a seedling cherry tree die from excessive leaf-curling aphids, but it’d also been really dry,” she said. “So I can’t say the insects did it altogether.”
Beneficial bugs fall into three categories: predators, parasitoids and pollinators.
Predators eat other bugs. Lacewings, ladybugs, praying mantis and garden spiders are predatory insects, feasting on aphids and other insect pests.
Parasitoids, such as stingless wasps, sustain their offspring’s life by killing a host insect. Parasitoids lay their eggs inside a living host, such as caterpillars or grubs. This ensures a safe, nutrient-rich nursery for parasitoid progeny at the host’s mortal demise.
Pollinators, such as bees, are beneficial in that they bring pollination power to yards and gardens. Want to learn more about beneficial bees? Read our Mason Bee blog post.
Some predatory or parasitoid insects may also seek nectar or pollen for protein or sugar. Woo them with easy-access flowers, such as broccoli, cauliflower, carrots, yarrow, dill and even dandelion flowers.
“They need shallow flowers and shallow nectaries they can reach easily,” Collman said.
For pests below soil’s surface, reinforcements come in the form of beneficial nematodes. These microscopic roundworms lay waste to many garden woes—grubs, borers, maggots, moths and more.
You can buy a box of 7 million at McLendon.
“People are having good luck with them,” she said. “They slither through the soil in search of root-feeding insects … go into the openings of the insect’s body, then multiply and multiply until they fill the insect and it bursts.”
To nail nematode application, be sure the soil is moist (remember, they slither) and is 50 degrees or warmer.
Control tent caterpillars, cutworms and other soft-bodied creatures without harm to beneficial insects using Bt, a naturally occurring bacteria.
Bacillus thuringiensis—Bt for short—can be purchased as concentrated liquid and applied to plants under attack. McLendon carries Safer brand Caterpillar Killer.
After ingesting Bt, a pest’s gut activates toxins within the bacteria. Those toxins dissolve holes in the pest’s gut, releasing Bt spores and killing the creature within a few days.
When garden pests appear—and they will—try blasting them with a hose or squishing them to death.
You didn’t get them all? Worry not, Collman says—your plants wield their own defense mechanisms.
“Plants expect that things are going to take advantage of them,” she said. “They’ll overproduce leaves to meet their needs.”
Plants also can change their chemistry and physical characteristics to defend against pests, she said.
When under attack plants release kairomones, a chemical that rallies beneficial-insect reinforcements.
“Kairomones let beneficial insects know (a plant is) under attack, and that there’s food there,” Collman said. “Plants are amazing things.”
If you must annihilate garden pests with a pesticide, consider using less-toxic methods. They’re effective and gently keep a yard’s yin and yang intact.
Least toxic are horticultural oils, soaps or minerals. Plant-derived insecticides, like neem oil and pyrethrins, are more toxic and should be used as a last resort. However, all are superior to broad-spectrum chemicals that kill all insects, pests or not.
“If there are outbreaks and you need to protect plants, it doesn’t have to mean doing the whole yard,” she said. “You might have to spray a few aphids, but just hit the aphids—not the whole plant.”
“Target the pest and protect the rest” is Collman’s mantra.
“Be willing to tolerate some insects,” she said. “And with the money you would’ve spent on pesticides, buy yourself a nice pair of bypass pruners.”
Soil Testing: University of Massachusetts or Simply Soil Testing USA
Read or download “Natural Pest, Weed & Disease Control” handbook
Read or download “Beneficial Insects, Spiders, and Other Mini-Creatures in Your Garden” from WSU Extension
Read or download Natural Lawn & Garden guides at www.gardenhotline.org
Or call for free expert garden advice: Seattle’s Garden Hotline, (206) 633-0224; the Snohomish County Master Gardener hotline, (425) 367-6010; or the Pierce County Master Gardener hotline, (253) 798-7170
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