Adult Colorado potato beetle

Summer brings numerous bugs to our yards and gardens; some are necessary and beneficial, others are destructive and invasive. There are so many pests needing management this time of year, but I will focus on the Colorado potato beetle. They are hardy insects with amazing reproductive capacity and voracious appetites. Last year, the potato beetle larvae ate most of the foliage off my potato plants, because I started fighting them too late. Now is the best time to start fighting back, before these beetles have a significant impact on your food crop.

The potato beetle took me by complete surprise in 2018. By the time I realized my plants were being attacked, there were beetles and larvae crawling all over the plot. Handpicking was not an option with such overwhelming numbers, though I did try. One trick I wasn’t able to try this year is to choose a short season potato and plant them very early, so the harvest begins in June/July. Instead, I planted a small section of potatoes a few weeks ago, and last week put in my main plot (I’m not recommending you plant potatoes so late in the season, I procrastinated). The small section was easy to monitor, and it did quickly attract beetles in early June.

Female beetles can lay over 300 eggs over their lifespan (a few weeks); the eggs are yellow and laid in clusters, usually on the underside of the potato leaves (although I did find some clusters on grass next to my plot, good reminder to keep potatoes mulched well). They can hatch within two weeks, and the larvae can complete development in 10 days, eating the tiny new leaves and quickly swarming the plant. The most mature larvae (fourth instar) will drop off the plant and burrow into your garden to become pupae. These large, bulbous pink larvae can cause almost 75 percent of the damage on your plants. According to the UMN Extension site on Colorado potato beetles, potato plants can handle up to 30 percent of its leaves consumed (defoliation) until around the flowering stage. Right after the plant flowers, the tubers begin to grow (bulk), and at this point the plant can only handle up to 10 percent defoliation before tuber growth suffers.

It is essential that you check your plot early and often, picking off beetles and gently removing all egg clusters. You likely won’t get all the eggs, which means keeping up on the larvae as well. The smallest larvae are tiny and tend cluster around new growth, especially the center of the plant. The larger beetles, which have orange heads and vertical yellow/black body stripes, will crawl all over the plants and sometimes hide on the ground near the stem. Move the leaves, and search in the morning/evening. My hatred for these bugs has overpowered my general queasiness at touching insects, so I’ve just been grabbing the beetles and squashing them into the ground. I squish the eggs between my fingers, and do the same to the larvae. If that sounds too hardcore for you, feel free to put on some gloves and put the eggs, beetles and larvae into a bucket of soapy water.

Colorado potato beetles will overwinter in your garden, and will emerge in the spring to feed on either young potato plants or other nightshades like tomato, ground cherry, pepper, eggplant, etc. Ensure that you pull out the old plants and keep the garden tidy, and planting potatoes every other year can help reduce beetle populations if you don’t live near anyone else who grows them. They are active from June through September, so eternal vigilance is key. Keep a sharp eye on your nightshade plants too, especially tomatoes. Since the beetles come from the ground, netting or other plant coverings will not protect against them. My advice is to have your kids/grandkids join in the picking, and make beetle management a “fun” chore.

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