Maine Organic Farmers and Gardeners Association
Controlling Colorado Potato Beetle and Striped Cucumber Beetle

Publications \ The Maine Organic Farmer & Gardener \ Spring 2003 \ Potato Beetle

By Eric Sideman, Ph.D.
Director of Technical Services, MOFGA

I can understand farmers who tell me they’re tired of hearing about the new USDA Rule and the regulation of organic vegetable production. I have said many times that the new rule is really 99% similar to MOFGA’s old standards, and I still claim that. Then why am I still writing articles about it? Because this is the time of year when we farmers are spending these very cold days leafing through catalogs and ordering seed and materials for meeting our dreams of glorious vegetable production only a season away. I can still say the regulations are mostly the same, because 99% of what organic production is all about has nothing to do with brand name materials. On the other hand, all of us do use some materials, and that is where that 1% of change is taking place.

That 1% of change is important to farmers who want to avoid problems with their certifier. Certifiers are being very careful now that their USDA accreditation may be affected if they mistakenly allow their certified farmers to use prohibited materials. The most problematic area for certifiers is the world of pesticides, where inert ingredients are trade secrets, and yet, if those inerts are prohibited synthetic materials, those pesticides are not permitted in organic production. Some materials that once were permitted in organic production for one reason or another are now prohibited because of their inert ingredients. We may get some of these products back as manufacturers reformulate with permitted inert ingredients. In the meantime, we growers may have to reconsider how we control some pests.

First, I want to stress that pest control in an organic system is framed by nonchemical practices. Cultural practices that prevent or block pests are the key methods, and chemical inputs, even if they are natural, are the last resort. Crop rotation, sanitation, timing and building barriers are not only desired but actually required where appropriate by the USDA Rule.

Colorado Potato Beetle

Toki Oshima drawing
Toki Oshima drawing
Colorado potato beetle (CPB) at one time was the reason many organic growers did not even grow potatoes. More than a decade ago, I was involved with testing Bt (Bacillus thuringiensis) products in Maine that targeted this pest. We organic growers knew Bt well from our experience with caterpillars of various kinds, but a Bt for beetles was new. It proved to be a valuable component of our tool kit when used in a timely fashion. Over the years most of the brands of this Bt fell by the wayside, because manufactures turned to genetic engineering to make their production more efficient, so their products were no longer allowed in organic production. One brand (Novador, also known as Colorado Potato Beetle Beater) retained the natural production method, so it became very popular. Now it too is not going to be permitted until the company reformulates, which they are doing. If you like to make such calls, you could call and thank Valent (the manufacturer; 1-800-89-VALENT) for its efforts. I hope Novador is back by the 2004 growing season.

In the meantime, I think some growers will have a hard time. Most will be able to control the CPB with other practices and materials. Remember the life history when choosing your approach. The beetle overwinters as an adult hibernating a few inches deep in the soil. In spring the adults become active about the same time that potatoes start sprouting. (Coincidence? I doubt it.) At that time they cannot fly, so they crawl around looking for potatoes, or eggplants, which they really like. A few weeks later they lay small masses of orange eggs on the undersides of the leaves. The eggs hatch into larvae, which do most of the damage.

The very small scale grower is still best served by hand picking the adults early in the spring and squashing the egg masses. Larger scale growers should rotate crops, and if new isolated fields can be used that are more than a half mile from where potatoes were the previous years, that should offer pretty effective control. Also, since the beetles crawl out of hibernation, a ditch lined with plastic can serve as a barrier between the new field and the old one, as the beetles fall in and cannot crawl back up the slippery plastic. Thick organic mulch also reduces populations, as the adults have trouble crawling out of hibernation.

A new product that will be on the market in 2003 should fill the gap left by the lost Bt. It is a new formulation of Spinosad called Entrust. The old formulation has had good reports but was unavailable to organic growers because of prohibited inert ingredients. Spinosad is a product of fermentation of a naturally occurring soil microbe. The material activates nicotinic acetylcholine receptors leading to neuromuscular fatigue and paralysis of the insects. It has low toxicity to humans and low environmental impact, because it degrades relatively quickly in the soil. It is active against caterpillars, some beetle and fly larvae, and even leaf miners, because it is absorbed into plant leaves. Dow has reformulated this material using permitted inerts, and it reportedly is going to get both OMRI approval and be approved by the new EPA program that will review materials for compliance with the USDA National Organic Program Standards. (Look for the words “for organic production” and three little green leaves on pesticide labels for that note of compliance.) Of course Entrust is likely to be expensive and in package sizes that are out of reach for small scale growers unless they share. Even when Novador comes back, I think Entrust will serve well in rotation with Novador in order to avoid the build up of insect resistance.

Cucumber Beetles

Striped cucumber beetles are the bane of cucurbit growers. The adults overwinter in the shelter of plant debris in and around the garden. They become active in the spring when the temperature reaches about 55 degrees F. and begin feeding on weeds and tree flowers. They migrate to cucumbers and their relatives as soon as vines appear. They can inflict severe damage at this stage, chewing off cotyledons and destroying leaves. They often gather in large numbers and can devour leaves. Early in the season they mate, and eggs are laid in the soil at the base of the plants. The eggs hatch in about 10 days, and the larvae crawl down and feed on the roots of the plant. In addition to feeding damage, the striped cucumber beetle also transmits bacterial wilt disease, which on its own can kill the plants.

Rotation does not control this pest very effectively, because cucumber beetles are good fliers, but sanitation can help a great deal. Keep the area around your fields mowed and free of trash. Plow down plant debris in the fall and plant a cover crop. Floating row covers make a great barrier that will keep the plants free from the pest, at least until the crops flower. Then you have to remove the covers to allow pollinators access. Remember to weed under the row covers, as these fabrics promote plant growth.

When sufficient control was not gained by cultural practices, many growers turned to pyrethrum products as a last resort. MOFGA used to permit a product call Pyrenone, which was pyrethrum with the synthetic ingredient PBO (piperonyl butoxide), a synergist that made the pyrethrum much more effective. MOFGA chose to permit it because it greatly reduced the number of sprays per season, which, in turn, we believed reduced the impact on beneficial and innocuous insects. But the USDA Rule does not permit PBO, so formulations of pyrethrum must be PBO-free and free of prohibited inert ingredients. At the time of this writing (late January), the only pyrethrum formulation I know that meets this condition is Pyganic, which can be sprayed right through the floating row cover if you see pests under it.

A relatively new, natural material called Surround, made from kaolin clay, has been showing good results in trials. It comes as a powder that is mixed and sprayed, so it coats leaves with a white film that confuses or deters the pest. It is being used for many pests in apple orchards and seems to hold promise for many vegetable pests. The white film could be a marketing problem if it is not washed off of produce, but will not affect marketing when only the unmarketed part of the plant is sprayed.

While the active ingredient of a brand name pesticide or fertilizer formulation may be permitted, ingredients not listed on the label may make a particular brand a clandestine prohibited product. To be safe, follow the OMRI (Organic Materials Review Institute) brand name list (at www.omri.org) and talk with your certifier.

Eric is available to answer your questions about farming and gardening
by calling the MOFGA office.
MOF&G Cover Spring 2003