Apple management week of May 20

By Terence Bradshaw

While it’s beautiful out now on Sunday evening, we certainly saw a significant apple scab infection period over the past 24-36 hours in every orchard across the state. If you weren’t protected with good coverage of a full-rate protectant fungicide going into this, then you’d best cover up ASAP. A material with good post-infection activity like a QoI, DMI, of SDHI material should go on within the next day or (at the latest) two. If you were not covered with a mancozeb or other EBDC fungicide, one of the DMIs like Procure, Rally, Rubigan, or of course the workhorse Inspire Super will help to manage cedar apple and other rusts, which are active right now.

With the cool weather, blossom fire blight is a non-issue. Insecticides need to stay in the shed until petal fall, but there are a number of them on the horizon that will require management as soon as possible. I’ve seen very high catches of European apple sawfly in a couple of orchards, and those should be managed right at petal fall to avoid significant damage to developing fruitlets. Trapping is really necessary to determine the need to get in early vs. waiting for timing to manage first codling moth hatch. On that note, we’re seeing codling moth in most orchards. The first flying adults aren’t to worry about, but tying their first catch in pheromone traps allows for accurate model tracking to time management against first-generation larvae. I caught CM in Washington and Orange counties on May 17, and expect to use that date for the biofix in the upland regions. In Bennington county, moths were flying solid week earlier. Management against codling moth should start between 100 and 200 degree days (base 50°F) after first catch, which should be sometime next week in many areas and orchards.

Overall, bloom looks good to great- I’m not seeing or hearing of much in the way of low bloom density, and some varieties are being reported with snowball bloom. Pollination conditions were very good overall, so expect to thin this year. It’s tough to make a specific thinning recommendation without seeing your specific orchard and knowing all factors. However, consider that a) bloom was good; b) pollination weather was good; c) no frost was experienced; and d) weather has been fairly stress-free (sunny, cool, just enough rain) so tree carbohydrates are plentiful. Chemical thinners tend to work based on competition among fruitlets, so these condition make thinning more difficult, and thus an aggressive tactic may be pursued. I recommend multiple passes of a moderate rate of thinners, starting at petal fall. Of course, keep an eye on things between sprays. Tagging specific fruitlet clusters and tracking fruitlet growth with a set of calipers will give you a sense of whether certain fruit will abscise, as fruitlets stop growing a few days before signs of abscission (yellowing stems, open sepals) are apparent. Keep thinning until you’re down to single fruit per spur, spaced six inches apart on the limb.

Dr. Duane Green from UMASS has a good list of general recommendations for using thinner materials at petal fall:

If you did not apply a bloom spray, make certain that you do apply one at PF. In some instances, application at both times may be appropriate.

· Carbaryl

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