Black fly

Swarms of biting black flies dampen my gardening enthusiasm from mid-May to September frost.

I’m often asked, “What’s the worst pest in your garden?” After cultivating this plot of land for 20+ years and coping with potato, asparagus and Japanese beetles, deer, voles, chipmunks, slugs, snails, and every known borer, caterpillar, and curculio in the Northeast, I’ve concluded that none of these are the ultimate garden wrecker.

The worst pest in my garden attacks the gardener, not the garden. Black flies, AKA gnats or buffalo gnats, ruin my gardening season. They breed in the stream that borders our property and emerge in mid-May, looking for blood. These tiny insects swarm around my head and shoulders and crawl through my hair, into my socks and sleeves. When they bite, they inject a toxin that causes swelling, redness, and intense itching for days.

I’ve spent years feeling guilty and lazy about the pots of perennials and shrubs left out behind the house all summer, waiting to be planted. My weeded spring gardens start to look like neglected lots by July. I’ve finally concluded that it’s not indolence after all; it’s the black flies. For nearly four months, I simply can’t be outside in my yard for more than 10 to 15 minutes without an onslaught of swarming, biting insects around my head. That’s hardly enough time to deadhead a rose, pull a few weeds, or plant a perennial.

Black flies require cool, fresh, moving water in which to breed. They’re most prevalent in areas with brushy growth and forested stream banks. Some black fly species only breed in the spring and hang around for a month or so. Unfortunately, some species hatch repeatedly all summer long. That’s the type that breeds in our brook, so we’ve got ’em right through September unless there’s an early frost. A rainy forecast increases their ferocity, so this year has been especially tough.

Recently, I learned that Bacillus thuringiensis ‘Israelenis’, the active ingredient in Mosquito Control Rings, also kills black fly larvae. Researchers recommend adding the dunks to the streams in early spring soon after the ice melts. I’m going to give it a try next spring. To keep them from floating away downstream, I’ll tie them in a mesh bag and attach it near the culvert that flows out of our neighbor’s pond. I’ve got nothing to lose and a whole gardening season to gain!

Ann Whitman,
Nursery Supervisor, Gardener’s Supply