University of Vermont

By Terence Bradshaw

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.

By Terence Bradshaw

It helps to read what you wrote after sending. This clarifies a question a grower had for me, now that I’ve re-read things. My post should have read “Fire blight remains a serious concern in any orchard that has open blossoms, apply streptomycin at 24 oz/acre plus 1 pint Regulaid (or other similar wetting agent)/100 gallons finished spray within 24 hours of a wetting event to any trees with open blossoms.”

I originally left the Regulaid out of that statement.

TB

By Terence Bradshaw

Today’s alert will be brief. Fire blight remains a serious concern in any orchard that has open blossoms, apply streptomycin at 24 oz/acre plus 1 pint/100 gallons finished spray within 24 hours of a wetting event to any trees with open blossoms. Organic growers, Serenade and possibly Double Nickel are your best options. That said, some sites have never seen fire blight, so this may be less important in cooler regions like the northeast kingdom or inland Vermont, but this is as big a potential infection event as I’ve ever seen. But remember, no blossoms, no need to treat. Symptoms should be showing next week if infection occurred earlier this week.

That said, and given the heat, spray nothing else until it cools down Sunday or Monday. Many sprays that are applied at this time of year (Captan, sulfur, thinners, many emulsifiable liquids) can cause leaf and/or fruit burn if high temperatures come soon after application.

When you do get in for a petal fall spray after cooler (<85°F) weather resumes, cover up for scab, and include a kick-back material if appropriate and you weren’t covered for these latest infections. NEWA indicates that all ascospores that could cause primary infections are mature and will be released in the next significant rain event but I wouldn’t put 100% faith in that. The European RIMpro model which takes many more factors than NEWA’s scab model into account still estimated 14% immature ascospores, and many orchards had a good bit of inoculum going into 2016, so prepare to stay covered for at least another week or two.

Insects are flying, and as soon as you can get into your orchard with no bee activity get a broad-spectrum material on the whole orchard. Codling moth are flying in virtually every orchard assessed, but their larvae are not yet a concern until moths mate and eggs hatch in a few weeks. European apple sawfly and plum curculio, however, are in most orchards now.

Thinning. I really can’t make a blanket recommendation, nor are any of the other specialists in the region. If you had good bloom, even with some king blossoms missing, and you likely had good pollination, then apply a mild to moderate thinner as soon as it cools off. Only on light-blooming blocks should you avoid thinning altogether. Reassess in a week. For what it’s worth, I intend to cover the UVM orchard with carbaryl only on Monday, then reassess at the end of the week. I know I’ll need to work a bit harder on the Empire and Honeycrisp, less on the Macs. But that’s my orchard. Yours is likely different.

Have a good weekend and feel free to shoot questions my way if you have them.