Early start for protection against codling moth
by KRISTIN KNIGHT - Ravalli Republic
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Rising temperatures are prompting early protection against wormy apples and pears this year.
Historically, the third week in June is the time to begin apple or pear codling moth pesticide application. But using the forecast temperatures for Hamilton and Corvallis, the “degree-day” model of the life cycle of the codling moth predicts that protection should begin about June 6 - two weeks earlier than normal.
The Ravalli County Extension Service uses a degree-day model of the codling moth's life cycle to time its control measures to have the greatest effect with the least pesticide use. Knowledge of the relationship between temperature and the speed with which the codling moth completes its life cycle allows apple growers to estimate the stage of the insect's development as the season progresses.
According to the extension office, each year pheromone traps containing a lure with female moth scent are set, telling growers when the moths have emerged from their cocoons and are laying eggs. Temperature data is then used to determine how quickly the eggs are hatching, and degree-days are calculated. The best time to apply any spray, whether conventional or organic, is when the eggs are just beginning to hatch. Sprays should then be applied to protect the fruit until nearly all eggs have hatched into larvae, or about one month.
The codling moth usually has two generations per year, and the number of sprays will depend upon the weather and the type of pesticide used. It is not necessary to spray for codling moth if your tree will not have a crop this year.
According to the extension office, several management options exist for controlling codling moths, including biological control, traps, mating disruption, cultural control and chemical control.
Biological control includes spraying with a bacteria Bacillus thuringiensis (Bt), which has mixed results and must be applied often - every five to seven days or more often if rainy. The bacteria must be eaten by the codling moth larvae as they find a developing apple to eat and make a tunnel into.
Sweet food baits attract lepidopteran adults and larvae. Codling moths are attracted to molasses and palm sugar bait traps with a 10 percent solution placed in yellowjacket domes and put into the lower canopy of trees. More female codling moths than male codling moths are attracted to molasses traps.
Codling moth pheromone traps are available at some Bitterroot Valley nurseries and garden supply stores. They catch only male moths and will not control females in most situations. However, the pheromone traps are important in predicting the first larval hatch. Ravalli County Extension uses the Oregon State University model based on local temperatures. Backlight traps that run from sundown until 11 p.m., reduced codling moth populations by 39 percent without catching large numbers of nontarget night-flying moths.
As for cultural control, backlight traps have shown some efficacy in small orchards for trapping adult moths. Remove any infested fruit well before harvest and destroy it to eliminate larvae. Remove brush and debris from the orchard, and remove bark scales from the tree to eliminate overwintering sites. Wrap the trunk with corrugated cardboard or burlap in late summer and early fall to trap migrating larvae. Periodic removal of these tree wraps to destroy larvae or cocoons is very helpful.
For chemical control, spraying spinosad (Entrust, Conserve) bimonthly when codling moth larvae first hatch has been most effective in combination with bimonthly alternating sprays of granulosis virus (Cydex, Madex and Virosoft), according to the extension office. Spinosad reportedly increases codling moth sensitivity to other insecticides. Neem and pyrethrins or mixes with rotenone can be sprayed to target first and second generation larval hatch. Kaolin clay (Surround 95 WP) can be sprayed weekly or bimonthly when apple blossom petals fall and fruit begins to form. Surround should be used in conjunction with first and second generation larval sprays since codling moth control is inadequate if used alone. To all chemical sprays, add 1 tablespoon per gallon molasses and 1 tablespoon per gallon insecticidal soap for increased efficacy. Spray in the evening.
For more information contact the Ravalli County Extension Office at 375-6611 or e-mail ravalli@montana.edu.
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