The Colorado potato beetle (Leptinotarsa decemlineata) is one of North America's most ravenous and difficult to control garden pests. The most common potato beetle, it is serious pest to potato and eggplant crops and is often destructive to tomato crops. But it can be controlled sustainably using a combination of integrated pest management techniques and cultural, biological, chemical, and physical controls.
Identification. As seen in the photo at right, the Colorado potato beetle (henceforth known as CPB because I'm too lazy to type Colorado potato beetle a million more times) is a yellow beetle with 10 black stripes.
Larvae (2 pictures, left) are orange or red with black head and legs, and the larger ones have black spots on the sides. When mature, they're 1/2" long. Look for them on the undersides of plant leaves.
Eggs (right) are usually found on the undersides of leaves in clusters and are yellow-orange.
Cultural control. Cultural control of CPB includes standard integrated pest management (IPM) practices. The best cultural control is choosing potato varieties with the earliest maturation rates in your growing zone–the earlier your potatoes are ready to pick, the better chances your plants have of surviving beetle infestations. Some varieties that mature early are Caribe, Norland, Pungo, Redsen, Sunrise, Superior, and Yukon Gold (75 to 88 days).
CPB overwinter (as adults) deep underground. As it gets warmer, they make their way to the surface, usually emerging by spring, when they look for an acceptable food source. (Probably, if they're overwintering in your yard, that means they had an acceptable food source last season.) Then they mate and the females begin producing eggs. So, an alternate form of cultural control–if you have a long growing season– is to wait and plant your potatoes until after the population of overwintering beetles have emerged and declined.
Crop rotation (locating the crop in area each season) is another cultural solution that is not always practical for the home gardener. Although crop rotation cannot completely eliminate the pest, it can slow it down. Floating row covers (right) can keep migrating beetles from accessing your plants. Floating row covers are made of a breathable white cloth that lets light and water through (not just plain clear plastic). You can get them at most garden supply catalogs…Gardens Alive is one example. Just make sure to monitor the plants beneath the row cover to make sure that no CPB were lucky enough to get trapped inside when you put the row cover on.
Finally, mulching your potato beds with straw can help delay CPB development.
Physical control. The home gardener with a small plot of potatoes can usually pick off adult beetles, larvae, and eggs. Drop them into a bucket of soapy water or vinegar and dispose of properly.
Biological control. There are some natural parasites and predators of CPB and you might be lucky enough to have those in your yard. Natural predators of CPB include lady beetles (ladybugs), lacewings, predatory stink bugs, and certain spiders. Two species of fly, Doryphorophaga doryphorae and D. coberrans parasitize CPB larvae, and one species of wasp, Edovum puttleri, parasitizes CPB eggs. You can't count on having these in your garden, but they are a good reason not to indiscriminately spray pesticides in your garden–you'll kill the good insects too.
Bacillus thuringiensis, or Bt, a naturally occuring bacteria that is toxic to many insects, has been proven to be very effective in controlling CPB. The Bt subspecies that is effective against CPB is called the san diego or tenebrionis strain. You can buy an insecticidal spray that contains the bacterium spores, or spray the bacteria directly onto the plants. Bt alone is worth a separate post….so in the next week I'll make a post that gives more information about the different types of Bt, where to buy them, and how to apply them.
Chemical control. CPBs have developed a resistance to the hardcore chemical pesticides of our parents' gardening days–think Sevin. So even if you're tempted to douse your plants with some evil chemical—don't, because it probably won't work. However, there are some botanical pesticide options that are available, although these are the least "earth-friendly" options.
Examples include products with rotenone, derived from the roots of a certain plant, and Pyola, an insecticide made from canola oil and naturally-found pyrethrins. Botanical pesticides derived from neem tree seeds have also proven effective. Brand names are Neemix, Margosan-O, and BioNeem. Be sure to read the directions carefully before buying and applying!!
Colorado Potato Beetle Organic Control Options, National Sustainable Agriculture Information Service
Colorado Potato Beetle Greenshare Factsheet, URI Landscape Horticulture Program
Adult–Image from Wikipedia, courtesy of USDA/Scott Bauer
Larva–Image 1 from URI, courtesy of Dr. Richard Casagrande; Image 2 from Wikipedia, courtesy of user "Pollinator."
Eggs–Image from Purdue University, courtesy of W. Crenshaw