While I was considering candidates for my least-wanted-insects list, I received an e-mail from a new homeowner who was desperate to end a plague of giant green June beetles. I, on the other hand, have felt wonder and delight when confronted by these B-52s of the insect world, with their brilliant coloration and improbable, clumsy flight. True, their larvae are root feeders, but my gardens are sufficiently in balance to ensure benign population densities.
That’s not the case for this homeowner, however. The population levels she reports are resulting in incessant human/beetle collisions that are spoiling her outdoor experience. Clearly, the green June beetle is her worst pest. And just as clearly, any worst-pests list will vary for each garden, season and year.
At the moment, besides working my market garden, I manage the Mountain Air Organic Community Garden (just outside Burnsville). This is a brand-new garden, and some pests — such as the Colorado potato beetle — have yet to find it. But the bugs that cause the most trouble both on my farm and at the Mountain Air are probably a safe bet to make most gardener’s short lists of unwanted visitors.
In both gardens, pest season opens with an onslaught of flea beetles. These guys can stop an early, direct-sown Brassica crop (such as turnips) in its tracks. And we don’t even want to talk about eggplant! Among the potential solutions to the flea-beetle plague are releasing beneficial nematodes, (see my “Before the Fall” column, July 2 Xpress), using row cover to keep the beetles out, and dusting your garden with diatomaceous earth (wear a mask and apply around dusk, for the sake of your beneficial insects).
There are reports of a hot-pepper/garlic spray working on flea beetles (direct contact with the pest is said to be required). Folks also use mineral dusts and wood ashes, but I’ve been unimpressed with the level of control these achieve. Finally, encourage birds (chickadees, titmice and warblers, among others) and toads, which prey on flea beetles.
Cucumber beetles are the next to arrive. These pests can worry young cucurbit seedlings to death. By far the easiest approach is simply to keep row cover over the plants until they begin producing female flowers. You’ll know the female flowers by the embryonic fruit at the base of each blossom. The male flowers come first, but until the females show up, they’re superfluous (heard that one before, guys?) — and quite tasty, stuffed. Try to choose squash and cuke varieties with multiple-disease resistance. Because once the plants are past the seedling stage, the main threat from cucumber beetles lies in their role as vectors of disease.
There is a product that combines copper sulfate (to control fungi) and rotenone (to control squash pests). Convenience is its selling point, but I don’t recommend this solution. At the cucurbit seedling stage, fungal problems are very unlikely, so applying copper sulfate — a persistent heavy metal — is pointless. Even more importantly, rotenone has been implicated as a causative factor in the development of Parkinson’s disease.
Here I must digress a bit. Cucumber beetles (and, for that matter, most of the “worst” pests) are intractable enough that the temptation is great to break out a powerful spray to “solve the problem.” But beware: Just because you’re using a botanical insecticide doesn’t mean it’s harmless. For example, I bought PyGanic as an organically certifiable insecticide insurance policy for Mountain Air’s Community Garden. Its active ingredient is pyrethrum flowers. Nonetheless, I’ve yet to use it because, from a whole-system-management perspective, it is too broad-spectrum and as likely to cause more garden-ecology disruption than any but the most desperate of situations warrants. The fact that the label advises wearing a respirator and a nitrile apron and gloves when applying it is another quite visceral disincentive! And the reason I bring this up here is that it’s key to my worst-pests strategy. The deadly certainty of the broad-spectrum impact of rotenone — and yes, even pyrethrum — is a devil’s bargain (or, as Richard “Dr. McBug” McDonald would say, “the nozzlehead’s path”). With two very important exceptions, our goal — a balanced gardenscape that’s free of pest outbreaks — requires more complicated, less sweeping measures.
Beneficial nematodes control the soil-dwelling, larval stage of cucumber beetles. The trouble is, these pests have such powerful olfactory apparatus that any within a quarter-mile of your garden will find it. I’ve actually grown parthenocarpic cukes (capable of setting fruit without pollination) in towers made of reinforced concrete wrapped in lightweight row cover. This effectively excludes all insects — including cucumber beetles. Territorial Seed does sell one parthenocarpic zucchini, but it’s even more expensive than the parthenocarpic cuke seed.
Diva, a new All-American-winner cuke, is both parthenocarpic and virtually bitter-free. And because bitter is what attracts the cucumber beetle, this one is way less prone to attack. It’s also a great cuke! A diversity of plantings, including many strong-smelling plants, should also help. And finally, consider installing a bat box (bats are significant cucumber-beetle predators).
Next on my list are cabbage loopers and the imported cabbage worm. The truth is, a diverse garden should attract enough predators of these pests to make them a nonproblem. But the one time diversity can’t be relied on is when broccoli heads up (caterpillars inside the heads are inaccessible to the predators). Usually, one spraying of BT (bacillus thuringiensis) solves the problem. Heavy rainfall may wash the BT away, so use a spreader sticker (such as Thermax) and re-spray after heavy rain. This is one of those two exceptions to the “no big-gun spray solution” rule.
The cabbage crop/pest situation really taught me to walk my talk. Although I always say don’t squish it if you don’t know it, I was doing exactly that with the yellow, web-bound eggs of a parasitic wasp that controls cabbage caterpillars. The cabbage looper is largely yellow, and it makes webs. I wrongly deduced, therefore, that these were cabbage-looper eggs and squished them diligently till Dr. McBug set me straight! This year, many of my kohlrabi had this beneficial’s eggs on them. I even witnessed one caterpillar in the process of being sucked dry. Hopefully, this would have straightened me out if Richard hadn’t already done so.
Squash vine borer is our next culprit. Its impact can be devastating: When the moth is laying its eggs, squash mortality is usually 100 percent.
I’ve avoided giving descriptions of these pests because of space limitations (and because I’m lousy at it). If you’re wondering what a particular pest is, the Cooperative Extension Service (and, often, neighboring gardeners) can enlighten you or confirm your suspicions. But learning to recognize the vine borer moth is a key to controlling it, so here goes …
The adult is a fat, dark blue or green moth that resembles a wasp when in flight. Its abdomen seems noticeably orange to me (in the Garden Problem Solver, Jeff Ball describes the abdomen as having red, black and copper rings). You’re most likely to notice it resting on the squash in the damp of morning and on cloudy, drizzly days. When you see this guy, it’s time to start spraying. Even if you don’t see him, you might consider a spray regimen around the second half of June. I use a combination of BT and Safer Insecticidal Soap. Theoretically, either one should work. The soap dries out the eggs, and the BT paralyzes the borer babies’ stomachs as they take their first bites, beginning the boring process.
You need to spray twice a week. Fortunately, since the moth lays its eggs at the base of the squash, only the stem area needs to be covered (but thoroughly). I spray from ground up, hitting about eight to 10 inches of stem.
There are many other options; I like some more than others. I’ve tried injecting BT into the stem ahead of the borer, but the results didn’t seem to justify the trouble. The classic after-the-fact remedy is surgery. You cut open the vine and remove the borers, then cover the wound with soil. The plant often lives, but productivity is usually severely impacted. The easiest thing to do is just grow the Moschata family of squash, which is highly resistant to the vine borer (butternut is the best-known member of this family). Another favorite of mine is Black Futsu. For some folks, the immature butternut suffices as a summer squash. Me, I’ll keep spraying.
Rounding out our rogues’ gallery is the Japanese beetle. As an introduced pest, it has fewer predators. (As you read this, however, Dr. McBug is in China, partly in pursuit of more predators). Richard has already raised our consciousness about the spring Tiphia wasp, an Asian Japanese-beetle predator that was introduced here back in the ’30s. He now rears and sells these wasps. Milky spore, a disease that controls the larval stage, has been of questionable quality in recent years. Moreover, to be effective, it needs to be released communitywide. (Otherwise, if you have the dinner plants of the beetle’s choice, these critters will just flock in from surrounding areas). If your problem is with Japanese-beetle larvae tearing up your lawn, then viable milky spore would be a good solution. Beneficial nematodes will serve the same function (i.e., infecting and killing the soil-dwelling Japanese-beetle larvae) for a broader array of pests. Handpicking (as described in “Before the Fall”) is actually quite effective.
Traps (available, at garden centers) can help reduce beetle numbers. The key with traps, which use pheromone and floral lures, is placing them 15 feet or so from your crop. Otherwise, you may attract more beetles to your plants than to the trap. My best solution is the serendipitous result of having plenty of still-untamed areas on the farm. The weedy version of evening primrose is the ultimate trap crop for Japanese beetles. Until I was mowing an area with evening primrose in it, I’d just assumed that I had few beetles on my farm. Now, however, I know that they’re out there: Our interests just don’t happen to conflict. But if primrose were a crop, these beetles would definitely be a problem!
There are many other pests (such as squash bugs , harlequin bugs, bean beetles and asparagus beetles) that may well make your personal “worst five” list . But this is my third column on pests, and I’m ready to move on. (I’m starting to feel like the director of the Department of Home Garden Security!) So if I didn’t include your least-favorite pest in my top five, catch me at the Wednesday-night Downtown Farmers Market — or at the Organic Growers School next spring.