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?
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: wood bugs. 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.
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.
The damage on the chard was different from the beans and kale. Instead of holes, I saw soft brown patches in irregular shapes. It looked a bit like a sunburn, not like typical bug damage. But from prior experience, I knew exactly what it was: leafminers. I’ve never seen one of these tiny insects with my own eyes, but I’m all too familiar with their effects. Instead of biting holes, they tunnel between the layers of tissue in the leaf. Their favourite meals are members of the Amaranthaceae family, including beets, chard and spinach. My rescue approach was similar to that with the kale, except that I skipped the power washing stage: I removed damaged leaves, did a harvest to allow space between each plant, and then covered the bed with floating row cover.
Several weeks later, the bugs have not returned and my plants are looking perfectly happy. Upon reflection, I realized that the bugs were simply responding to my two or three weeks of relative garden neglect during a busy travel period, during which time my plants became overgrown and stressed. With the right diagnosis and approach, you can deal effectively with most pest issues. Here are my top five tips:
- Inspect your plants regularly. If there’s damage, use your detective skills to figure out what’s causing it. You can always google “carrot pests” or “what’s eating my lettuce”.
- Use floating row cover to prevent flying insects. This multi-purpose fabric doesn’t look pretty, but it’s incredibly effective at preventing all manner of pests, from cabbage moths to carrot rust fly and many others. Just keep in mind that it will also keep out bees, so don’t use it on anything that bears fruit.
- Keep your plants healthy and well-harvested. Healthy, strong plants are less likely to be attacked than stressed plants. That means fertile soil, appropriate watering and regular harvesting. Keeping our plants from becoming overgrown, and harvesting enough so that there’s air-flow around each plant, is one of the most effective ways to prevent both pests and plant diseases.
- Remove the damage as soon as you see it. Put damaged leaves into the compost. They’re likely to harbour eggs. To remove caterpillars or aphids from remaining leaves, try squishing them by hand if you can bear it, or using a medium-strong jet of water. Just be sure to follow best practices for appropriate water use during our current heat wave.
- Plant beneficial flowers. One of the most effective and ecologically-appropriate ways to prevent pests is to plant beneficial flowers that attract predatory insects, such as ladybugs, hoverflies and predatory wasps. There are many beneficial flowers, but my personal favourite is smoky fennel, a a tall self-seeding herb that requires zero care and is a favourite hangout spot for all kinds of friendly insects. Bonus: the entire plant tastes like black liquorice, with seeds that make a great breath freshener.