The Colorado potato beetle can be combated


Colorado potato beetles. (Bigstock)
Contributor April 9

The common potato is not so common in home gardens, and here’s why. First, people who have never dug fresh new potatoes don’t know how good they taste. Second, their first crop might have been wiped out by Colorado potato beetles and they’ve never tried again.

This much-studied pest was first seen not in Colorado but in Iowa. “This insect,” wrote entomologist R.A. Casagrande in 1985, “resulted in the first large-scale use of insecticides on an agricultural crop . . . influencing generations of agriculturists to depend upon this unilateral approach for managing this pest and others.” And to little avail. From Paris Green to DDT, to the highly toxic neonicotinoids of the present day, the beetle has developed resistance to every chemical employed to destroy it — even the popular Spinosad formulations, created by fermenting a natural soil bacterium.

Barbara Damrosch is a freelance writer and the author of “The Garden Primer.” View Archive

Scientists theorize that the beetle acquired this power through its coevolution in Mexico with potato-related host plants, which were full of natural toxins. In addition, our overeager blanketing of crops with poisons has actually encouraged resistance, because only resistant individuals survive to breed. We’d do well to heed Casagrande’s thought that “the solution may require a reevaluation of many practices throughout agriculture.”

Meanwhile, professional growers continue to play potato beetle hopscotch, substituting new poisons for banned ones, or alternating one spray with another of a different class. Many use safer, more sustainable tactics as well. Crop rotation, always worth doing, is most effective on a large scale, with miles, not feet, between crops. Timing plantings helps, too, but because this prolific little creature can have three broods per year, with eggs, larvae and adults all occupying a plant at once, it’s a finicky process.

Here’s what a home gardener can do:

Grow the vegetable organically. Potatoes fed with a manure-based fertilization program have been shown to have higher yields. Seaweed, either fresh or in liquid fertilizer form, is also great for potatoes. Well-grown, vigorous plants will net a decent crop even after defoliation by the beetle, if it occurs when they are mature enough.

Mulch the plants with straw. Such a mulch was shown, in a Virginia trial, to temper soil temperatures and retain moisture. Accordingly, yields were greater and they required less spraying.

Exclude the pest with floating row covers that are secured at the soil surface right after planting. Check plants often in case some overwintering beetles have emerged from the soil.

Hand-pick. Large-scale growers use vacuum rigs and flamers to pick pests, but a small plot is easily managed by hand. Look for striped adult beetles that emerge in spring and knock them into a can of soapy water. Rub off any bright orange patches of eggs they’ve laid on the undersides of leaves. Squish or drown the plump, pinkish larvae that hatch from these eggs and do the most damage. Keep checking throughout summer. You won’t get them all, but greatly reducing the numbers will save your potatoes, and the more you pick, the more you’ll reap.

Damrosch’s latest book is “The Four Season Farm Gardener’s Cookbook.”

Tip of the week:

Forming a crisp edge between the lawn and plant beds is a simple way to freshen the yard in spring. Use a sharp spade to create a one- to two-inch deep vertical edge between the grass and the bed. Guide the line first with string pinned with long nails. If you attempt to eyeball the line, the edge will look crooked. — Adrian Higgins

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