Colorado Potato Beetles

Errrr… Colorado Potato Beetles

I have grown potatoes in many parts of the United States and until this year did I have a single potato beetle show up for dinner. I am dead serious. Never. I have always heard about potato beetles I even looked them up once in an old class book from my days in college (Horticulture Science) so I even knew what they looked like, but I had honestly never seen one in my garden.

The first time I picked one up, I was really very intrigued. They really are very beautiful beetles. They look like a very neat and tidy, efficient little bug. And they are. They increase their resistance to most pesticides after too long. I have read that the development of many insecticides/ pesticides can be laid at the foot of the Colorado Potato Beetle. So, cultural practices play an important role in the management of potato bugs, as they help minimize the need for insecticides, protect natural predators, and prevent the development of pesticide resistance.

I also believe the concept of crop rotation, although until the last few years, I have never practiced it. (I know, I KNOW) but I’ve always had small gardens, mostly what I could actually eat fresh. Potatoes were often a luxury I did not have the room for and I had this idea in the back of my mind that I had to have LOTs of them planted to eat very many and often didn’t bother. (Can anyone say “Mental Block”?) The most success I have ever had is growing potatoes in tires. This gardening method saves space and grows a super large number of potatoes. (Read about the issue of rubber as a growing medium in the article) Regardless of how I’ve grown them, never a potato bug in sight…. until this year. Errr. Now I know that all they say about the hungry beetle is completely true.

Why organic methods are important in dealing with Potato Beetles

I have read on various health lists of the most important foods to buy organic is potatoes. I assumed it was because being a root, it would “hold” more of the pesticide and you cannot wash it off, being stored in its tissue, but this isn’t entirely true. I won’t go into the history of the potato beetle (you can read that at the references listed at the end of this article) but suffice to say, they have a legendary ability to develop resistance to a wide range of pesticides used for their control; and many a pesticide is being used to keep them at bay in the industrial farming community. Potatoes are consistently on the Dirty Dozen food list and Jeffrey Moyer, who is also farm director of the Rodale Institute.

“I’ve talked with potato growers who say point-blank they would never eat the potatoes they sell. They have separate plots where they grow potatoes for themselves without all the chemicals.”

I have read often that “This insect pest is one of the best known beetles, famous for it’s ability to devour vegetables in the nightshade family: potato, tomato, eggplant and peppers. The adult beetles as well as their larvae can strip the plants of leaves and ruin an entire crop, if left to their own devices.” I didn’t want to leave them to their own devices, so I started hand picking them off (like a good little organic gardener) of two 4’x26′ foot growing beds, full of young potato plants. I thought I had them on the run, five whole days without finding a single adult potato beetle! Yeah for organic gardening! But the SIXTH day I found holes covering most of the newest potato leaves and very small Potato Bug larvae munching down.

The potato beetle’s rotund adults are nearly a half-inch long, pale yellow to burnt orange, with five black stripes on each wing cover. In late spring, after coming out of their winter hibernation in the soil, they break upon the world with one thing on their minds: finding something to eat. They walk toward their quest as they gain the strength to fly, looking for potato plants or their relatives. Once a food source is found, they will lay eggs within 5 to 6 days, laying clusters of 15 to 25 bright yellow-orange eggs on the undersides of the leaves. What hatches are the soft-bodied, hump-backed larvae that look a little slimy and are easier to squish.

The tiny larvae start out small but grow very fast, molting four times into larger stages called instars. The last instar grows up to be fat little orange eater, and as I discovered, they are the ones to eat the most of my potato leaves. After having their fill they crawl down into the soil and pupate. From this resting stage, yet another generation of adults emerges by the end of the very same season, ready to eat again before passing the winter underground. New potatoes, main crop potatoes, late potatoes, they eat them ALL! They can produce upwards of three generations per year. And the thought that keeps me up at night is… how many are now in the ground awaiting next years crop? Eeeeck!

Vern Grubinger from University of Vermont Extension has this to say about the potato beetle’s history, it is very interesting.

It’s amazing that not long ago, this serious pest of vegetables pest was a harmless, well-behaved insect. It fed only on the buffalo bur, a tough weed that grows along the eastern foothills of the Rocky Mountains. Then, about 150 years ago, the beetles discovered a new food growing in the white man’s gardens. It adopted the cultivated potato as its favorite food, spread rapidly, and we’ve been fighting Colorado potato beetles ever since.

It happened like this: with the opening up of the West following the Mormon migration to Utah in 1847 and the California gold rush of 1849, pioneers arrived by the thousands and many of them planted potatoes. By 1855 potato growing reached westward to the native home of the beetle, and the insect started to spread eastward along the routes traveled by the pioneers.

By hitchhiking and flying with the prevailing winds, the beetle migrated about 85 miles a year. It reached Nebraska in 1859, Illinois in 1864, Ohio in 1869, and the Atlantic coast in 1874. This caused great alarm overseas, and almost every European country banned the importation of American potatoes. Europe’s potato growing regions remained free of potato beetles until after World War One, when they appeared near Bordeaux, France, where there had been concentrations of American troops and supplies. Now the beetle is widespread in Europe, too.

Prior to the coming of the Colorado potato beetle as a pest, the name “potato bug” was used to describe a different beetle that is a relatively minor pest on potatoes. Now called the “old-fashioned potato bug”, this long slender beetle has two black stripes on each wing cover. The adult feeds on potatoes but lays its eggs in the ground and the predatory young feed on grasshopper eggs and the like.

How to Get Rid of Potato Beetles

By changing the location of host plants, crop rotation is one way to suppress potato beetle populations because it makes it slightly harder for them to get to their food after they emerge in the spring. The problem is, the potato beetle is very mobile so long distances are needed between last year’s potato planting and this year’s in order to have much of an effect. This makes a crop rotation for pest control unfeasible for the home gardener. (The soil/growing benefit of plant rotation is entirely different, and quite an important practice for even the smallest garden.) The professionals say, “Even a few hundred feet doesn’t help much; a few thousand feet may help; but a mile or two is better.” Now I ask you, do YOU have that much gardening space to work with? I know I don’t.

Another helpful practice is mulching the potatoes with straw after an early-season planting. This can reduce the Colorado potato beetle’s ability to locate potato plants. The mulch helps create an environment that favors beetle predators. The straw should be spread so it is touching the potato plants, but only a light layer of straw mulch is needed. Another way to protect plants is to place lightweight floating row covers over them and then seal the edges, well before the beetles arrive.

Natural Predators of the Colorado Potato Beetle

Biological Control
High fecundity (a fancy way of saying, the capacity of producing young in great numbers!) usually allows Colorado potato beetle populations to withstand natural enemy pressure. Still, in the absence of insecticides natural enemies can sometimes reach densities capable of reducing Colorado potato beetle numbers below economically damaging levels (Ferro, 1985).

The lady bug or lady bird beetle will be happy to eat up your potato beetle eggs. Another reason not to use even the safest of controls i.e. Diatomaceous Earth. I deliberated and whined over making the decision to use this for these beetles and for our squash bug problems. DE will kill lady bugs too, the same way it kills the potato beetle, by desiccating it. Diatomaceous Earth’s killing actions are mechanical. Insects cannot become immune to its action. Insects come in contact with the powder or ingest it and literally dry up and die within 48 hours.

I gave in and spread some around, I noticed a drop in the potato beetle population for about a week. Just as the weather warmed up, the eggs (that the DEAD lady bugs didn’t get to eat) hatched a whole new generation. As I contemplated (hey, sometimes thinking things through takes some real time!) I began to see a lady bug or two come back around. That was all it took, I went back to hand picking. If you are remotely interested in learning about the history of pest control tactics, please read resources below, it is quite interesting, how we got to where we are.

I had never seen an “Assassin Bug” until the Colorado Potato Beetle showed up in our garden. I had never seen one, didn’t know what it was, but there were as many of them as their were potato bugs in the garden, well, maybe not quite, but certainly a noticeable presence. My son was helping me glean potato bugs from the plants one evening and said, “Oh, look!”. He called them by name and told me all about them. (I knew I did something right raising that boy. 😉 And he did spend a lot of his childhood playing outside with bugs, gathering them to feed his “other animals”, but I digress.

It was then I started truly noticing them. Now while a quick breeze through the internet doesn’t specifically call for them as beneficial insects to the Colorado potato beetle. I can tell you from personal experience that they are. The only two bad bugs I see doing real damage in our garden are the potato beetle and the squash bug and I have assassin bugs crawling all OVER the potatoes. I have seen them attack and kill a potato beetle and I sure do wish I had a video of that!

However you choose to protect your potatoes, there are a few constants. Pick them off when you see them and keep your soil healthy. Strong plants can resist a potato beetle attack far better than plants struggling to survive before they showed up.