Saturday, July 2, 2011

Pests and diseases: Colorado Potato Beetle

Colorado Potato Beetle (adult stage)
Colorado Potato Beetle (larvae)

Colorado potato beetle (Leptinotarsa decemlineata)

We've been battling Colorado Potato Beetles for much of the previous month. If you are not trying to keep them off your potatoes, you’re trying to keep them off of your eggplants and vice versa. Amazing how a relatively small insect can strip a seedling of its foliage in a matter of a day or two. By the time a “herd” of potato beetle larvae make themselves across a seedling, you're most often left with stems and ragged little shreds of foliage, all of which will be delightfully coated in the excrement from the Colorado potato beetle adults and larvae.

Life Cycle

Adult Colorado Potato beetles, about 3/8” long, emerge from overwintering near previously infected crop plantings. The adults have alternating yellow and black stripes that run along its back. The larvae stage, are orange-red with a dark head and some spotting. After feeding for several weeks, females lay masses of yellow-orange eggs on undersides of leaves. Females are known to lay close to a 1,000 eggs in their short life span of several months. Eggs hatch in four to nine days and the larvae can feed for two to three weeks, they then pupate in soil. The adults will then emerge in five to ten days, most areas will see two generations. There can be three in southern states.

Plants Affected

Potato, eggplant, nicotiana, petunia and certain nightshade weeds are preferred foods of the Colorado potato beetle adult and larvae.

Adult Colorado potato beetle and larvae chew on the foliage of host plants. Damage typical of the adults is notching wounds along the leaf margins. The larvae however can cause the most damage to seedlings, leaving much more ragged injuries, resulting in devastating foliage loss. Foliage may also be soiled with excrement. When large outbreaks occur entire plantings may be stripped of foliage.

There are many controls available to home gardeners and commercial growers to help combat this nuisance pest. Small scale home gardeners can venture out to the garden early in the morning and shake adults onto a drop cloth, then dropping collected beetles in a bucket of soapy water. Hand picking of both the adults and larvae is another option for home gardeners. Scouting on the underside of foliage for Colorado potato beetle eggs and destroying them by squishing them is another option. Mulching plants with at least four inches of straw (to discourage larvae from pupating in the soil) and floating row covers until harvest or mid season can be very effective methods of control.
On a larger scale, releases of five spined soldier bugs can be an effective, non-spray approach, as well as releasing parasitic nematodes in the soil to attack larvae.
When cultural and biological controls have not solved the problem, organic controls such as Entrust (Spinosad) applied via backpack sprayer or tank sprayer to foliage of potato plants or the foliage of other damaged crops. This should be applied as soon as you see Colorado potato beetle adults or larvae. Correct timing of applications and appropriate application rate is particularly important to maintain when using Entrust, so as not to develop resistance to Spinosad. Waiting until the infestation is severe will result in heavy loses, repeat spray as necessary to maintain control.
At last resort introducing Pyganic into your spray program for these crops can be effective in maintain population control of the Colorado Potato Beetle. When applying any pesticide be sure to read labels thoroughly and follow mixing and spray instructions specific to infestation. Always wear personal protective equipment as stated in label instructions.

“The Organic Gardener’s Handbook of Natural Pest and Disease Control” Edited by Fern Marshall Bradley, Barbara W. Ellis, and Deborah L. Martin
“The Ultimate Guide to Backyard Bugs Garden Insects of North America” by Whitney Cranshaw
“Vegetable Notes” published by U Mass Extension, written by R Hazzard

Article by Sonya Reynolds, Greenhouse Coordinator, Johnny’s Selected Seeds


Rita Jacinto said...

These little buggers are quite voracious. I have them in the green house, where I grow veggie starts for sale, as well as out in my fields. I have had very good luck in the green house with the pheromone traps that are available. You can make your own by soaking a cotton ball in allspice oil or any other oil high in eugenol. Staple the cotton ball to the middle of a yellow sticky trap and hang them just above the foliage.

I do have a question too, about application rates for Entrust. the directions on the bag are for very large farms...what is the application rate if I am only mixing up 5 gallons at a time?

Andrea at Johnny's Selected Seeds said...

Hi Rita,
Thanks for sharing how you're handling these pests.

You can find the Entrust application rates for smaller volumes listed on the label under "Rate chart for small plantings"

Here's the label. You can find what you're looking for on page 3:

Let us know if we can help with anything else.