June 3, 2016
By now all orchards should be past petal fall and many fruit are sizing up into the 10 mm range. There are a number of factors to consider in the week ahead. Rain is expected Sunday through Wednesday of next week.
Apple scab should still be protected against. Even though the NEWA models show complete ascospore maturity and likely release of all mature spores for all sites, the RIMpro model still suggests that there may be mature spores ready to be released in next week’s rain. This is also an important time for management of powdery mildew (PM) and cedar apple rust, so fungicide coverage is warranted for those as well. Captan has no effect on the latter two diseases, so if using it for scab you’ll need to add another material such as a strobilurin (Sovran, Flint), SDHI (Fontelis, Luna), or DMI (Inspire, Procure, Rally); mancozebs applied now (only at the 3#/acre rate, and not if you have used a higher rate earlier this season) will provide protection against rust but not PM. For organic growers, sulfur remains the most effective material against scab and PM, but has little to no activity against rust. Early results from spray trials I ran last year showed some effect of low-rate copper (Cueva, Badge) on rust, but there is risk of fruit russeting so caution is advised.
Insect activity is picking up in Vermont orchards. Eric Boire from CPS is monitoring traps in several Champlain Valley orchards and all had captured codling moth (CM) by May 26. I would conservatively use May 21 as the biofix date for CM in the NEWA system. First sprays for CM should be applied at 250 degree days (base 50° F) after biofix, and all Vermont orchards are approaching that target so the next spray should include a material effective against this pest. Many materials have good activity against CM, please check the 2015 New England Tree Fruit Management Guide for specific materials (CM is listed with the ‘Int(ernal lep)’ column in Table 7.1.1). Bt, while generally effective against most lepidopteran (caterpillar) pests, has poor efficacy against CM in my experience. Plum curculio remains active in Vermont orchards, and European apple sawfly may be active especially in orchards bordering unmanaged apples, so a broad-spectrum material is likely warranted for this next application.
Thinning is still an important consideration for many orchards and must be evaluated on a case-by-case basis. In blocks with many fruit remaining in clusters, application of a thinner is recommended.