Petal Fall and Hail Damage Management

May 27, 2014

I’ve heard reports of possible hail damage from today’s storms, particularly in Addison County (although I would appreciate word from any other affected areas). Mary Conklin from UConn Extension just offered this advice to growers similarly hit recently in Connecticut:

1. Fireblight susceptible pears and apples should receive a strep spray within 24 hours of the hail storm if damage occurred. However, if you applied Apogee you should be covered because it protects against Fireblight.

2. If you have young trees that have not received Apogee AND had Fireblight last year (or your neighbor has/had Fireblight) AND were hit with hail – apply Strep within 24 hours of the hail storm.

3. Apple varieties still in bloom (there aren’t many locations with bloom still on) that were hit with hail need strep applied within 24 hours.

4. The fruit of stone fruits that are cut should have fungicide coverage maintained to prevent rot fungi from taking hold if you plan to harvest any of it.

5. Perennial canker/Cytospora canker fungi will move into trees through wounds, including those caused by hail. Pruning out damaged or broken limbs will help to prevent this destructive disease from taking hold.

6. Severe hail damage that causes young tree leaders to break: re-leader them ASAP.

7. Blueberries with hail damage are more susceptible to Phomopsis because the organism is more likely to infect where canes are damaged. In addition, spores are released between bud swell and petal fall and blueberries are in bloom now. If you (or your neighbors) have or had Phomopsis in the past, maintain fungicide coverage.

8. Call your crop insurance rep.

With that out of the way, this is a good week to get your petal fall coverage on. Apple scab, while most ascospores should be spent in the Champlain and Connecticut valleys, should be protected against for another 7-10 days. Powdery mildew is a concern at this time, as is cedar apple rust. DMI and, to a somewhat lesser degree against rust, Strobilurin fungicides, are effective, but be sure to mix with a protectant to reduce risk of fungicide resistance in your orchard. Petal fall insects (plum curculio, sawfly, early codling moth) need tending to.

Thinning is a real crap shoot this year, with extremely variable bloom and moderate to good to poor pollination weather, depending on site and cultivar. Cool, cloudy days of late suggest that moderately higher rates of thinners should be applied, but low blossom density on some cultivars may negate that. I would suggest a cautious approach and suggest following the recommendations in the 2014 New England Tree Fruit Management Guide. For most varieties, that would be 2-3 oz Fruitone plus 1 pint Sevin per 100 gallons dilute (based on tree row volume). Notice that’s by the book, I’m not pushing a more aggressive strategy unless you indeed had a good to great bloom.

This is a great time to try the apple carbohydrate thinning model on NEWA (click on the ‘crop management’ tab at the top of the page) to assess the relative stress level of your trees to tweak thinner rates. Remember, fruit and shoot development at this time demand more resources (photosynthate) than the tree produces. Cool weather with moderate sunlight and a fairly low crop load reduce stress on the trees and make thinners less effective, all things being equal.

Terence Bradshaw, UVM Tree Fruit and Viticulture Specialist

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The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM Grant, and USDA Risk Management Agency Funds.

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