Methods for dealing with Colorado potato beetles are almost as numerous as the critters themselves. Researchers in Maine reduced CPB damage with fish emulsion spray; they hypothe that size increased crop vigor, rather than repelled or suppressed CPB, explains their results. Two ladybird beetles, a fly, six ground beetle species, some predatory stink bugs, and a wasp (Edovurn puttleri) prey on/parasitize CPB; the wasp provides good control on eggplant, says University of Rhode Island (probably based on research in New Jersey, where it's warmer than New England). Conservation and augmentation of these and other beneficials is suggested by New Alchemy researcher Dave Simser; conservation of beneficials can be enhanced by using least toxic (to beneficials) strategies. Lastly, in a few years hybrid potato varieties with sticky hairs that repel CPB and other pests will be available. Below are some further ideas to consider.
Rotate crops (several hundred yards): "The most important practice in managing the CPB," say the six New England ag colleges in a 1990 publication. Rotate to crops other than potato or eggplant.
Plant early varieties: Suggested by URI. Early varieties can escape serious damage by maturing before peak CPB feeding: 'Caribe' (75 days) is the earliest URI recommends, 'Yukon Gold' (88 days) is latest. See April '89 National Gardening magazine or March '90 American Vegetable Grower for URI's suggestions; combine with next item.
Plant early: Suggested by URI. Plant as early as you can (3-4 weeks before last spring frost) as part of a system to escape peak feeding; combine with above item. Plant all potatoes early (do not stagger plantings).
Plant late: Suggested by URI. Riskier than planting early, but has always worked for one URI researcher. See two preceding items; do not plant early and late.
Shake plants: Suggested for gardeners by Dave Simser. Using a deep cardboard box, walk along plants once a week before bloom, shaking foliage into box. University of New Hampshire suggests hand-picking, if begun early in the season (but shaking can be easier).
Use row covers: Farmer Bill Palmer has had excellent results with spun-bonded protective covers (several brands available; don't use slitted type) for past three years in eggplant in Connecticut. Eggplant, unlike potato, is a warm-season crop that is not very vigorous. At Pennsylvania State University, excessive heat under row covers increased potato foliage, but not tubers. Row covers tearing or lifting out of the soil also has resulted with potatoes. However, UNH states spun-bonded row covers over potatoes "may help in the early part of the season." Hilling potatoes requires removing covers; irrigation pipe or 2' x 4's are easier to remove than if soil is used to seal row cover edges. Wide (48') protective covers allow more room for vigorous potato growth and are quicker to remove than narrow row covers. Do not use row covers if a solanaceous crop was planted the year before.
Bacillus thuringiensis (B.t.), variety San Diego: Bacterium specific to CPB; trade names: M-One (ph. 800-462-6866) and Trident (ph. 708-699-1616). M-One will reportedly begin, in 1991, to use a genetically-engineered bacterium. Trident, made by Sandoz, will not use genetic engineering through 1991, and Sandoz says they have no plans to. When I said that some people may prefer a non-engineered strain, and that this might be factored into their market analysis, a Sandoz rep seemed receptive. At any rate, URI says it's only a matter of time before CPB becomes resistant to B.t. var. san diego; rotating (using widely different types) of insecticides delays insecticide resistance.
Another naturally occurring insecticide which is registered in New England in 1990 for CPB is Noxfire (rotenone), which, according to Cooperative Extension, should be used with the synergist piperonyl butoxide. Rotenone is a plant extract, and it is said that piperonyl butoxide was originally derived from a plant. Being a plant extract doesn't imply human safety, but it does ensure the substance breaks down. Rotenone and piperonyl butoxide are very toxic to fish, and safety equipment should be worn. Kryocide (sodium fluoaluminate) is the trade name of the naturally occurring mineral cryolite, and like rotenone, reported to be fairly effective on CPB by URI. Research at University of Massachusetts found kryocide to kill only the larval stage of CPB, yet more effective at low temperature (65'F) than B.t. var. san diego. In 1981 University of Connecticut suggested Kryocide for gardeners, as it was registered with EPA for most vegetables and considered "essentially non-toxic." Check with Extension for latest info.
Apply thick mulch: At UNH, 3.5" of mulch (apparently hay) in 1989 reduced CPB and more than doubled potato yield. UNH theorizes mulch was too thick for CPB to emerge, and that mulch encouraged predators and parasites (URI reports 6 ground beetle species and a fungus prey on or parasitize CPB). Mulching too early slows soil warming; too late allows beetle emergence. Results need confirmation in 1990.
Note: Always scout your fields and obey pesticide labels, and consult your state Cooperative Extension.