September 26, 2018
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How to control garden pests without chemicals

Courtesy of Griffin Dill, Univer | Courtesy of Griffin Dill, Univer
Courtesy of Griffin Dill, Univer | Courtesy of Griffin Dill, Univer
Tobacco hornworm, a common pest in Maine that is known for attacking tobacco and tomato plants.
By Aislinn Sarnacki, BDN Staff
Updated:

Courtesy of Griffin Dill, University of Maine Cooperative Extension | Courtesy of Griffin Dill, University of Maine Cooperative Extension
Courtesy of Griffin Dill, University of Maine Cooperative Extension | Courtesy of Griffin Dill, University of Maine Cooperative Extension
The Japanese beetle is a common pest in Maine that attacks a variety of plants, including raspberries, roses and beans.

With Japanese beetles attacking the beans, worms infiltrating the corn and aphids sapping the life from the tomato plants, a garden can sometimes feel like a battlefield. Instead of spraying plants with synthetic pesticides, organic gardeners are finding creative ways to defend their crops. In many cases these solutions are simple, eco-friendly and effective.

“Oftentimes people are surprised at how simple the solution is once they identify it and work with us,” said Kate Garland, horticulturist with the University of Maine Cooperative Extension.

In the garden, the first step to winning the battle is simply showing up.

“Being in your garden on a regular basis is huge,” Garland said. “I’d say that’d be your number one step in pest management. In your garden, you’re noticing any problems very quickly so you can address any issues early.”

Then, once you discover a problem — such as a pest — the next step is identifying it, because while synthetic insecticides are often very broad spectrum and kill a wide variety of pests, nonchemical management solutions are often tailored to only affect specific species.

Gardeners can try to identify pests using online references and field guides, or they can send pictures by email or samples of their pests by mail to the University of Maine Cooperative Extension office in their county, the University of Maine Insect and Plant Disease Diagnostic Lab in Orono, or the pest experts of Maine Organic Farmers and Gardeners Association.

“For the vegetable pests I work with, the key is to get to know the biology of the pest,” said Eric Sideman, crop specialist for the Maine Organic Farmers and Gardeners Association. “That’s why identification is the first step.”

Once the pest has been identified, experts like Sideman and Garland offer suggestions to gardeners on how to manage the pests and save their plants. The following are a few examples of how to deal with some of Maine’s most common garden pests without the use of harsh chemicals.

Hand-pick them

Especially for household gardening, simply hand-picking pests from your plants may be an effective solution. This management method is used often with Japanese beetles, which gnaw on the foliage of raspberries, beans, roses and other plants. Holding a jar of soapy water beneath the beetle, you simple tap the leaf it’s on and it will instinctively drop straight down into the water, Sideman said.

“You can collect thousands of them when you’re diligent,” Sideman said, “and they can’t fly out of soapy water.”

While simple, the timing for hand-picking can be important. Japanese beetles emit an aggregating odor, meaning the longer they exist in one location, the more of a chance they have to attract others.

“So it’s very important to [hand-pick them] in the evening because you don’t want them to be there sitting all night calling their friends,” Sideman said.

Courtesy of Kate Garland
Courtesy of Kate Garland
Squash bug eggs are found on the underside of the leaves of a squash plant in July by Kate Garland, horticulturist for the University of Maine Cooperative Extension Penobscot County office.

Another common pest that can be effectively hand-picked is the hornworm, which destroys tomato plants. Because these green caterpillars are so well-camouflaged, Garland suggests hand-picking them at night with a black light, which makes them much easier to spot.

Garland also hand-picks and destroys the eggs of certain pests. She recently used her nails to scrape the tiny tan eggs of squash bugs from the undersides of pumpkin leaves. She then squished the eggs between her fingers and dropped them to the ground, snuffing out the pest before it hatched and became a problem. She’s done the same for the eggs of Colorado potato beetles, which attack potatoes, and leaf miners, which take down plants like Swiss chard and spinach.

While Garland often hand-picks pests with her bare hands, she says gloves offer easy protection from insect bites and any skin irritants, such as caterpillar hairs.

Courtesy of Art Shaw
Courtesy of Art Shaw
Row covers are one way to protect your plants from certain pests, as well as wind and harsh temperatures.

Create barriers

“Quite a few pests are easy to manage without the use of chemicals by using physical barriers such as row covers,” Garland said.

Row covers are tunnels of garden fabric — often held up by wire — that allow a high percentage of sunlight through. Not only can it act as a barrier against harmful insects, but it also can protect plants from wind and harsh temperatures.

Other important types of barriers are nets, which are effective in keeping mammals and birds out of plants such as berry bushes, and fences, a barrier used throughout Maine to protect crops from the state’s abundant whitetail deer population.

Clean up debris

In some cases, old plant matter and other debris can serve as a shelter for pests. Squash bugs, for example, often crawl under decaying pumpkin and squash plants to weather the winter, Sideman said. If you have a squash bug problem, one way to manage them is to clean up the pumpkin or squash patch each fall.

Trick and trap them

Sometimes you can use a pest’s tendency to hide in debris to your advantage. Garland has done this to get rid of slugs and earwigs. She’ll lay a wooden board or a piece of a hose on the ground beside a crop, and on a sunny day this little bit of shelter will attract the earwigs or slugs. She then picks up the board or hose piece and scrapes the pests into a soapy bucket of water.

Rotate crops

Courtesy of Griffin Dill, University of Maine Cooperative Extension
Courtesy of Griffin Dill, University of Maine Cooperative Extension
A Colorado potato beetle, a common pest in Maine that eats potato plant leaves.

Some pests have life cycles that involve overwintering in an area, therefore, it can be effective to move crops from year to year, alternating them between beds, Sideman said. The Colorado potato beetle, for example, hibernates in the soil during the winter, and in the spring, it emerges and walks to nearby potato plants. In fact, it can’t fly. It has to walk. Moving the potatoes from year to year is an effective way of keeping down their population.

Attract predators

Companion gardening is a practice that involves planting certain crops together that benefit one another in different ways, and it can be done to manage certain pests. An example of this is planting tomatoes with alyssum, Sideman said. Tomato plants are often plagued be aphids, and alyssum flowers attract flies and wasps that eat aphids.

Zap, water or Dustbust

Sometimes taking care of pests is so simple it’s silly. Such was the case when Garland recently found one of her ornamental catalpa trees covered with aphids.

“The aphids were flightless — there are some that are — and so these ones I just simply sprayed off with a forceful spray of water,” Garland said. “I knocked them to the ground, and they’re not mobile enough to repopulate the plant.”

In other cases, Garland used a bug zapper to knock Japanese beetles off plants, and she’s used a Dustbuster to suck up cucumber beetles that had infiltrated a row cover. In fact, she uses a Dustbuster to remove pests from plants on a regular basis, and it’s proved effective in keeping populations down.

Trap crops

A trap crop is a sacrificial plant that attracts pests, luring them away from your other plants.

“Then you can hand-pick the pests [off the trap crop] or Dustbust them, and in some cases, spray them, but then you’re spraying a smaller area,” Garland said.

Use natural insecticides

Not all insecticides are harsh, synthetic chemical mixtures. One effective insecticide that organic gardeners use is a natural, soil-dwelling bacteria called Bacillus thuringiensis, or Bt for short. Mixed with oil, this bacteria is sprayed on plants to kill caterpillars, such as hornworms, cabbage worms and corn earworm.

“[Corn earworm] is the insect that gets in and eats the tip of the corn,” Sideman said. “People are usually grossed out by finding it … When the corn is silking, the moth for the corn earworm lays eggs on the silk and when the eggs hatch, the caterpillars crawl down and start eating the kernels.”

To combat this pest, Sideman suggests spraying a Bt solution on the corn after the silk dies, allowing for pollination to take place first. The Bt then kills any caterpillars roaming around.

For more ideas on how to manage pests without the use of harsh chemicals, check out the “Resource Guide for Organic Insect and Disease Management,” which was written by Eric Sideman and four other pest management specialists. A free PDF version and a $20 hard copy of the book is available here.

For pest identification and questions about pest management, there are several options. You can call MOFGA at 207-568-4142 or email Eric Sideman at esideman@mofga.org. Or you can call the UMaine Cooperative Extension office in your county, the numbers of which can be found here. Or you can contact the UMaine Cooperative Extension Insect and Plant Disease Diagnostic Lab by calling 207-581-3880 or emailing clay.kirby@maine.edu.

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