UVM Apple IPM: Fruit set, insect activity picking up

Now that we’re past petal fall and many have had a chance to assess the effects of any thinning sprays applied last week, it’s worth assessing the situation as we head into summer. I have not made many orchard visits yet this year but have seen a few, most of my observations are from our own UVM orchard in Sout Burlington. Fruit set and thinning are all over the map for us, but overall we have a bit more fruit than I like, and we’ll be pitting on a middle0rate 6-BA (Maxcel) application tomorrow before things warm up for the weekend. Other growers are reporting good thinning with some need for retreatment, and at least one has feared overthinning. Remember that as fruit get larger than 15 mm diameter they will be unresponsive to most thinners, so our window is closing. For those lucky enough to have peaches, now is the time to thin those, too. This is usually a manual job, but there is a new thinner, Accede, but it is rather late for it to be effective. Remember to refer to the New England Tree Fruit Management Guide for thinning and other spray recommendations.

Insect activity has been pretty low but picking up. Anyone trapping codling moth should have recorded your first date of capture, this sets your biofix for when to start accumulating degree days to time sprays for the first generation. In South Burlington, we caught our first moth on May 17, and from then until today we have recorded 229 degree days (DD, base 50°F) using the NEWA calculator. Eggs are just starting to hatch, and optimum timing for treatment with most materials is around 250 accumulated DD. We’ll be adding Delegate to tomorrow’s spray mix to catch those hatching larvae, as we expect to hit that threshold by Saturday. Plum curculio are still active for 308 DD after petal fall (which I am calling 5/21 for us), so I am adding a second Avaunt treatment to that spray tank tomorrow. I did see some fresh damage in border trees yesterday. The choice of two different relatively expensive insecticides is to cover the spread of pests that are active right now, and to get ahead of populations before they breed and subsequernt generations proliferate. Based on Dr. Jaime Piñero’s efficacy summaries, Avaunt is excellent against plum curculio but moderately effective against other insects, and Delegate is an excellent material for lepidopteran pests. We have not used organophosphates at the UVM orchard for many years, so do not use Imidan which could cover all of the insects of concern. Verdepryn or Voliam could be good choices, but I don’t have them in the spray shed.

Apple scab should be done in most orchards but we don’t know until we’ve done a thorough assessment after primary ascospore release is finished and any infections have had time to develop. I saw no scab yesterday, but we will be including captan as coverage for any potemtially developing infections and to provide protection against summer diseases and rots before we back off into our summer schedule.

If you’re applying nitrogen fertilizers, you have just a couple more weeks to get your last applications on before we start to compromise winter hardiness.

All for now, Terry.

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