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Sunday, April 21, 2019  Spokane, Washington  Est. May 19, 1883
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News >  Home and garden

In the Garden: Identify the pest before choosing the remedy

Gardening is such a delightful pastime that rewards us with fresh produce and beautiful flowers. When occasional problems crop up, they can dampen our enthusiasm.

My garden has been growing well but that doesn’t mean there haven’t been a few hiccups along the way.

Two months ago, I started noticing small black beetles on a few of my calendula blossoms. I mostly ignored them but started to get irritated when I discovered they love to dine on the flower heads. While researching them, I learned they are blister beetles, so named for the caustic substance they secrete that is dangerous to animals that inadvertently eat them and causes welts and blisters on human skin.

Since I avoid using chemicals, I took a container of soapy water out to the flower bed and proceeded to tap the beetles, one by one, into the water. Sixty beetles later, I now have a nearly pristine calendula patch and am tickled it was so easy to deal with them.

This spring, my broccoli bed was besieged by hungry slugs. Oh, how I despise those slimy critters. Their calling cards are trails of slime and large holes in the leaves. One other insect that also causes holes is the green cabbage worm, but since I keep my plants covered with fine netting, I knew cabbage butterflies couldn’t lay eggs on the leaves.

How does one deal with slugs? Organic slug bait is one option. I’ve also found that trimming the lowest leaves of the plants that touch the ground eliminates a slug’s preferred method for climbing up into a plant. Another option is to sink an empty cat food or tuna can into the soil so the top lip is even with the soil surface and partially fill it with beer; the yeast attracts the slugs, they fall in and drown.

Pillbugs were another challenge for me early in the season. These generally benign crustaceans think the tender stems of young seedlings such as melons, squash, cucumbers and broccoli are delicious. I sprinkled diatomaceous earth around the base of each seedling to create a barrier until the seedlings’ stems toughened up.

Diatomaceous earth is a powdered substance made from the fossilized remains of algae. The tiny sharp edges cut the skin of certain insects, causing them to dehydrate and die. It is an organic product available at garden centers. I recently learned there are two brands imported from British Columbia – Last Crawl Insecticidal DE and APL Diatomaceous Earth – that have been banned by the EPA for being contaminated with trace amounts of dioxins. Other brands are considered safe.

I still have a mystery pest dining on the foliage in one of my potato beds. I initially suspected Colorado potato beetle larvae but have never seen orange eggs on the leaves’ undersides, the larvae, or an adult beetle for that matter. I thought it might be slugs but there’s no sign of them either.

No matter what type of insect is causing trouble in your garden, it’s crucial to identify the culprit before deciding on a management strategy. Sometimes it’s obvious which insect you’re dealing with but some insects are only active at night. I’ve been known to go out to my garden with a flashlight to see if I can spot any nefarious activities taking place.

If you need help identifying an insect, contact the Master Gardeners in Spokane County at (509) 477-2181 or in Kootenai County at (208) 446-1680.

Susan Mulvihill is co-author of “Northwest Gardener’s Handbook” with Pat Munts. Contact her at View this week’s “Everyone Can Grow A Garden” video at

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