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“When everything works just right, the population will be successfully suppressed but only for a short period of time,” Mr. Wood said. “Spraying must continue every two or three years - indefinitely, and over a very large area (to be effective).”
And while spraying throws the moth population into imbalance, it also kills off the beneficial organisms: the parasites and predators on the insect larvae. Citing recent
studies which show that these bene-, ficial wasps and flies “do a lot of good” in controlling gypsy moth populations, Mr. Wood recommended that if a decision is made to spray, the area covered be as small as possible so as to protect the natural predators.
“All environmental and safety aspects aside, from an economic standpoint it makes sense to spray as few acres as possible,” he added.
Spraying could be “a waste"
Mr. Wood emphasized that spraying won’t prevent the moth from becoming well established throughout the county. In feet, he maintained, “it’s a waste of time and money to consider spraying before there’s lots and lots of moths.” The most accurate measure of the moth’s population level is an egg mass count, and to justify spraying, there should be at least 500 egg masses per acre. “That’s the threshold,” Mr.
Wood said. (Each egg mass contains about 1,000 eggs. Depending on weather conditions, eggs are laid between July and September. The velvety masses average about 1 1/2 inches long and about 8/4 inch wide. Covered with buff or yellowish hairs, they are most often hidden on the shadey side of trees and walls or underneath rocks and logs.)
If the decision is made to spray, the state will shoulder part of the cost, provided that egg mass counts are high enough to justify the control effort. Proposals on cost-share spraying for next spring must be submitted by this November. Cost
per acre runs $7.50 to $12 and the county’s share varies between $3 and $5, according to John McCarthy, assistant to the Board of Supervisors and chairman of the gypsy moth committee. He noted that the figures are for spraying alone and do not include otter associated costs.
Should the county pursue this option, “we’ll need a gypsy moth coordinator on a full-time basis for at least a few months,” Mr. McCarthy noted. Prior to spraying, the coordinator, who will be responsible for supervising the egg mass counts, must supply maps for the area to be sprayed and must secure the written permission of all landowners in the coverage zone. “The more acres sprayed, the cheaper the cost per acre but the greater the difficulty in getting permission from all the landowners,”
Mr. McCarthy pointed out.
He added that the committee is compiling a list of businesses that will contract with individual landowners or groups of landowners for small scale spraying of ornamentals and shrubs.
Chemical or biological?
Once a decision to spray is reached, the next question is what and where to spray.
The most effective suppressant is Dimilin, a chemical insect growth regulator that interferes with the formation of the insect’s exoskeleton. Only those insects that eat Dimilin-coated leaves during the
caterpillar stage of development are affected. “It has a low toxicity to mammals and causes no harm to honey bees or adult insects,” Mr. Wood noted.
“When everything works just right, Dimilin achieves a 90 to 95 percent reduction in the gypsy moth population,” Mr. Wood continued. “That sounds like a lot, but really it’s what’s required to control the nui
88.9%