At the UVM Horticulture Research and Education Center, we caught our first codling moth in our pheromone traps on Thursday, May 26. Using that day as a biofix, we start accumulating degree days (base 50°), or rather let NEWA accumulate them, and plan to apply a treatment at egg hatch. Most literature references 220 DD as the beginning of egg hatch, but the NEWA model suggests treatment just a bit later at 250 DD for most materials to improve efficacy and ensure that more larvae contact treated materials or surfaces. A second application would be applied 10-14 days after that to cover the entire generation. In order to reduce the likelihood of CM evolving resistance to specific spray materials, be sure to rotate materials so that no two successive generations receive the same class of material. There are a number of materials effective against CM, compared to the old days when organophosphates and pyrethroids were the first and often only materials to come off the shelf. Heather Faubert published a nice summary of materials effective against codling moth here a couple of years ago. Avoid using ovicides (materials targeted at eggs rather than larvae) like Rimon or Esteem at this time, as those should have been applied around 100 DD for best effectiveness. For resistance management, check the IRAC code on your material and be sure to rotate codes so that no two generations see the same material. This includes applications made against other pests, i.e., if you apply a neonicotinoid (IRAC 4A) against apple maggot in a few weeks, that also counts in your resistance considerations for CM. Since many growers rely on a neonic application for summer management of apple maggot, I suggest not using one now.
However, there’s more to the story. We have been trapping CM in some orchards in northwest Vermont and have seen widely variable catch numbers. At HREC, we have only caught that one moth, which indicates a low population in a pheromone-baited trap; at another orchard, over 40 moths have been caught. Unlike for some other pests, there is no “spray when you see X caught insects” threshold for codling moth. The rule of thumb is that captures over five to ten moths in a week suggests a high population that warrants two treatments per generation. However, a low population, as observed at HREC, may be treated with a single application at around 360 DD, or sometime next week.
This tailoring of spray application to the specific life stage of the pest, based on empirical scouting and use of accurate weather and pest models, is an excellent example of how modern IPM, using a combination of scouting, weather data, accurate models, and modern pesticide chemistries are combined to dramatically reduce environmental impact of apple pest management and likely save the grower a few dollars, too. If you’re not trapping but rather rely on the default ‘first catch’ date in NEWA or a general calendar-based timing, I do not recommend a single treatment for the first generation, you should default to two. Advanced IPM requires a thorough knowledge of your orchard and pest systems, you can’t just wing it, cut your sprays, and assume that you’ll get the best effectiveness.
Other things to think about: Nitrogen fertilizers should be wrapping up in the next week or so. All sprays should include a calcium product, and on bitter pit-prone varieties, you may want to consider making specific calcium sprays every 10-14 days until harvest. Keep an eye out for fire blight- we saw our first strikes this year on inoculated trees in one of Dr. Kerik Cox’s trials at HREC. Thinning should be done now- if you need a little more in high-value varieties hand thinning is the way to go. Scab should be done for most orchards aside from the cooler upland ones, so you could take a break in the Champlain and Connecticut valleys if you’re scab-free at this point and plan on next fungicide in a couple of weeks when the summer diseases ramp up.
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