Colorado Potato Beetles

Adult potato beetle.

Ozarks Gardening
Copyright 2012, Jim Long

The Colorado potato beetle is a major pest throughout most of North America. It was first recognized as a pest in 1859 in potato fields in Colorado. The beetle had previously only grazed on buffalo bur, a distant potato relative. But when pioneers who moved West, began planting large fields of potatoes, the beetle adapted to the increased food supply. In the wild, the beetle had to travel up to a quarter mile to find buffalo bur plants, but with the new fields of one crop, the potato, it had only to hop from plant to plant. By the mid-1870s, the potato beetle had expanded its range (at the rate of 85 miles a year),  all the way to the East Coast.

The arrival of the potato beetle caused farmers and gardeners to search for ways to control the bug. An infestation of potato beetles could wipe out hundreds of acres of potatoes in ten days. There were all sorts of inventions, mixtures and unsuccessful attempts at finding a solution. It was only by accident that a gardener who was painting his house, and probably in frustration at the beetles, threw the remains of his house paint on beetle-infested plants. The bugs died! The ingredients in the paint included something called, “Paris green,” an inorganic compound that was commonly used in wall paper, artists’ paints and house paint. Soon chemical companies were providing Paris green to farmers, to be mix with water or dust directly on to the plants. Within three or four years the beetles developed immunity to the poison and lead arsenic was added. Both compounds are highly toxic to other insects including ones that are beneficial in the garden, as well as dangerous to birds, wildlife and most specifically, to the humans who dusted or sprayed the plants (and to those who ate the potatoes later).

Potato beetle larvae, eating leaves.

The cycle continues to this day, with chemical companies readjusting their formulas about every three years as the beetles continue to evolve resistance. One method that large-production potato growers use, is to use an assortment of different pesticides, week by week as the season goes along, trying to stay ahead of the beetles’ adaptations and resistance to the other formulas. Today we know how dangerous lead arsenic and French green compounds were, but many of the newer formulas may prove to be as dangerous.

Larvae cluster together and devour leaves, sections at a time.

Home gardeners can easily prevent potato beetles from being a problem. My method of early planting of potatoes in late January to early February, always misses the emergence of the beetle. By the time I’m digging my potatoes, the beetle is just hatching out and searching for potato plants. But gardeners who planted later, combined with the abnormally early season, will likely experience potato beetles. In small numbers they don’t pose a problem and it’s easy to pick the beetles off by hand and drop them into a bucket of soapy water. Spraying isn’t necessary. To prevent them becoming a pest, be sure to plant potatoes early in the year next season.

Happy gardening!