The Lepidoptera Complex

Mating disruption lures work by saturating the orchard air with female scent to prevent the male from ever finding his nuptial mate. Granulosis virus works in much the same way as the more familiar Bacillis thuringiensis, only with the advantage of infecting subsequent generations where conditions favor its establishment in wild populations. My own preference for a spray material for all internal feeding caterpillars is ryania, a botanical insecticide that works on contact as well as by ingestion, but unfortunately no longer on the registered market. An organic formulation of spinosad has proven equally effective against a wide range of lepidopterous species but resistance issues here demand a knowledgeable restraint on overuse. Surround kaolin clay confounds the sensory perception of the females, causing them to forego placing eggs in well-covered trees. Summer oils that smother eggs and larvae alike may have a place in defending orchard borders. Pure neem oil has the potential to provide a double whammy in this regard in my opinion. IPM growers have the option of making a "Last Call" for both codling and oriental fruit moths, which as chemical options go, has proven to be a very thought-out means of limiting orchard-wide distribution of pesticide.

The timing of sprays for any of these species is an exact science thanks to research on degree-day (DD) tracking. The countdown of degree days for codling moth (CM) begins with the capture of the first moth in a pheromone wing trap, hung out when the blossoms open. Traps are hung at eye level within the southeast quadrant of two centrally located trees. Degree days are calculated by subtracting a 50°F base temperature from the mean daily temperature (add the daily high and low, then divide by two). Mating doesn't begin until twilight temperatures stay above 60°F.

Can you picture the male moths hanging out after petal fall? "Hey, Joe, what temperature you got now? . . . Only 58? Shee-it!"

The first expected egg hatch for CM occurs when 243 DD have accumulated, and that's the day to make a first spray application of Bt, spaced thereafter at 4-5 day intervals for the next two weeks. Each larva must encounter the toxin and ingest it within the one to two days it negotiates its way from the hatching site (often on the underside of a leaf) to entry into the fruit. Using molasses as a feeding attractant and fish oil as a UV inhibitor increases the effectiveness of this baseline biological approach. Two applications of granulosis virus cover this same period (as did ryania, when it was still available). Get good coverage up high, as codling moths fly towards the light of the moon.

Growers in regions with multiple generations of codling moth should continue to monitor pheromone traps after the first emergence flight has peaked. Poor abatement of the first generation results in a continuing worry to the tune of thirty to forty eggs per subsequent female. When an average of five or more codling moths per trap per week are captured again, begin a 175 DD countdown to initiate successive sprays. Summer target dates come closer together, as growth and development is most rapid in the warmest weather. Here's where spinosad plays a potential role in targeting second generation lesser appleworm (LAW) or oriental fruit moth (OFM) as well. These smaller relatives of the codling moth have development cycles that run just slightly out-of-sync with their better known cousin. Timely removal of drops, especially beneath early-ripening cultivars, will lessen pest buildup of all three in the orchard.

The big picture of the "Lepidotera Complex" turns out to be a much broader question than one species alone can pose. As always, we need to give credence to the uniqueness of each orchard site. Proximity of wild trees holds merit here in both good and not-so-good ways. Moth migration can be limited by removing wild trees within 100 yards of the orchard. On the other hand, the proximity of external refugia plays a role in reducing the risk of resistance development in any one species to spray materials. Beneficial predators also thrive in unmanaged trees where caterpillars are more likely to be abundant.

A mixed species scenario determines the logic driving management choices. It's always difficult to outline a spray schedule and not be heard as advocating for more than just spraying. You must put together a number of methods and materials, and not place too much faith in any one of them alone. Growers who successfully employ Trichogramma wasps against first generation codling moth, for instance, may indeed find mating disruption of subsequent generations to be the "missing link" for adequate control. We also would be wise to remember some of the old ways of reducing overall moth pressures.

The ropes of twisted hay tied around trees a century ago were intended as a preferred hiding place on the trunk for moth pupae. Codling moth larvae ordinarily crawl out of fallen fruit to seek seclusion beneath the rough bark found on the lower trunk. Some larvae enter hibernation for the following year, while others return in the next generation. Hay twists would be burned before the succeeding moths took flight, just as organic growers today might burn corrugated cardboard sheets (duct-taped around trunks) for this same purpose. Ancient cultures across Europe celebrated St. John's Eve with bonfires to inspire the sun to sustain crops. The summer solstice also marks the time when codling moths are actively laying eggs. Hmmm . . . moths fly at night . . . moths are attracted to light . . . bonfires burn bright. Orchardists who honor past custom by lighting pruning brush piles on a warm evening (not too long after fruit set) will see streams of moths flying down the tree rows to consummate a deep pagan understanding of degree day timing.

Organic Orcharding Articles

• An Intelligent Paradigm
• My Apple Orchard by Laura Ingalls Wilder
• Honoring the Orchard Ecosystem
• Holistic Core Values 
• Holistic Disease Management
• The Kaolin Clay Strategy
• The Lepidoptera Complex
• Borer Insights
• Seasonal Checklist for the Home Orchardist
• Apple Grower Network Research Pages