When bugs attack! Five ways to deal with pest damage

Insects play important roles in our ecosystems. But sometimes, pests can get out of hand. Our role as gardeners is to understand what bug attacks are telling us, and then gently guide them away.

Caterpillar on a kale plant in the urban vegetable garden.
I found this cabbage moth caterpillar taking a nap after eating holes in our kale leaves. Photo by Rebecca Cuttler.

Recently, I returned to the garden after a couple of weeks of travel to discover that things had turned into a jungle. Our pea plants, which has been small when I left, soared over my head. Our tomatoes had sprouted multiple branches. And our kale, chard and bean plants were full of Swiss cheese-style holes. Someone had been eating them.

Bugs are a common garden problem. You plant your first lettuces of spring with so much hope and promise, only to wake up one morning and discover they've been decimated by slugs. You admire your bright red nasturtiums until aphids move in and take up residence.

Insects of all types play important roles in the balance of our ecosystems. Just like bacteria in human guts, the vast majority of insects are harmless or beneficial, and pests only become a problem when our plants are vulnerable or stressed. Our role as gardeners is to understand what bug attacks are telling us, and then act as stewards to gently guide the them away.

There are many different pests that can plague our crops, and it's important to identify them correctly in order to determine the right approach. But how do you figure that out, when there are ten different critters that munch similar-looking holes in leaves? And once you've identified them, what do you do?

Beneficial flowers like fennel attract ladybugs, hoverflies and predatory wasps

Beneficial flowers like fennel attract ladybugs, hoverflies and predatory wasps to your garden. Photo by Rebecca Cuttler.

Good observation skills are more important than an encyclopedic knowledge of insect species. Upon discovering the bug attack, I crouched down to the soil level and spent some time looking really closely at the nature of the damage. Our young bean seedlings had holes in their leaves, but there was also damage to the stems. Foliage that was close to the ground was affected, but any growth that was a bit taller was unscathed.

From this, I deduced that the culprit was a crawling creature — not a flyer. My suspicions were confirmed when I scratched the surface of the soil and saw them: woodbugs. That's who was causing my problem. Although primarily helpful decomposers, these land-dwelling crustaceans can sometimes go after young seedlings.

The damage was quite severe and my plants were too weak to sustain much more, so I took the desperate measure of sprinkling some diatomaceous earth on the soil in a circle around the plants. Diatomaceous earth is a natural substance made from fossilized algae that cuts the bellies of crawling things. I use it only as a last resort, because it can kill beneficial insects as well as the bad guys. Next year, I might start my bean seeds in cardboard egg cartons to give them a head start.

Cabbage moths are a common sight in the garden. Their caterpillars can wreak hav

Cabbage moths are a common sight in the garden. Their caterpillars can wreak havoc on brassica plants. Photo by Rebecca Cuttler.

The damage to our kale was, at first glance, similar to that on the beans. Lots of round holes. But a closer look revealed some differences. The bites were higher up on the plant, so it must have been a flying or climbing insect. And the stems weren't damaged, just the leaves, some of which were reduced to skeletons.

Then I saw it. A big, fat green caterpillar, happily snoozing on a kale leaf. You know those cute white butterflies you see in your garden? They are cabbage moths, and they lay eggs on members of the brassica family (including kale, broccoli, cauliflower and, of course, cabbage) so that their larvae can eat the leaves. I even saw some caterpillar poop sitting nearby and on unscathed lettuce leaf.

With the kale, my approach was different from the beans. I began by removing damaged leaves. Then, since the plants were small but fairly well established, I did a moderate harvest to allow for extra space between each plant, making it harder for the caterpillars to move from plant to plant. Next, I sprayed the plants down with a medium-strong blast of water, concentrating on the undersides of leaves where eggs and cocoons might be. Kale is tough enough to take a light power washing, unlike more delicate plants.

Finally, after allowing the leaves to dry and inspecting them again, I covered the entire bed with a big sheet of row cover material. This cloth, made from spun polyester and available at most garden supply shops, provides a physical barrier that keeps bugs out, and is effective for many pests. As a bonus, it's reusable and helps regulate soil temperature and moisture.

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