I’ll follow up with more details later- this announcement is meant as a notice in case anyone like myself needs to get their hands on some streptomycin today- but the NEWA fire blight models are predicting increasing likelihood of infection over the weekend as temperatures climb. If you have open blooms, be prepared to cover in the event of rain or to add strep to your spray tank if applying thinning sprays in the next few days. I’ll reach out later today with details on thinning, the insect situation, and disease management.

-Terry

—

Terence Bradshaw (he/him)
Associate Professor, Specialty Crops
Interim Chair
Department of Plant and Soil Science
College of Agriculture and Life Sciences

University of Vermont
117/210 – Jeffords Hall | 63 Carrigan Dr
Burlington, VT 05405

(802) 922-2591 | tbradsha
https://go.uvm.edu/pssbradshaw

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The cool weather is leading to a number of conditions in Vermont apples. Where trees are in some state of bloom, blossoms are opening very slowly. This is extending the overall bloom period. But also helping to maintain viability of pollen, styles, and stigma. It may be taking a while for pollination to happen, but we also have more time for it to happen. At our twilight meeting in South Burlington last Friday, despite the cool weather, there were abundant wild pollinators in the UVM orchards. For inland and upland orchards at pink or even earlier, the weather is delaying blossom opening. I don’t know of any orchards at petal fall but I haven’t been to the warmest corners yet. I would not expect them to be yet, but movement on bud stages is around the corner as weather is expected to warm into the 70s this week.

For growers headed into petal fall, a heavy bloom, and minimal to little cold damage from the April 25 freeze, it would be wise to consider a petal fall thinner. Petal fall means just that- no blooms in the orchard, so if you still have some varieties in bloom do not use carbaryl, an insecticide that is particularly toxic to honeybees, in this spray. I would consider NAA (Refine, Fruitone, etc.) alone or, if petals are truly off, with some carbaryl. Again, where bloom is heavy and conditions for pollination were good, plan to thin on the heavier side. Rates for many thinning materials are very confusing, and include spraying in parts per million, rate per 100 gallons dilute tree row volume, and the usual amount per acre. For most orchards, if a label (use https://www.telus.com/agcg/agribusiness to look up your latest labels) allows it, it’s easiest and totally relevant to default to the amount per acre as you usually do. Refine 3.5 WSSG, for example, gives a table and five paragraphs of information on page three about determining ppm for apple thinning, then one sentence, “Concentrate spray: Use Refine 3.5 WSG at the rate of 0.25 lb per acre (4 oz)-0.50 lb per acre (8 oz) in sufficient water to ensure good coverage at petal fall to early fruit set. Uniform and even coverage is crucial for good results.”

To summarize it, if you have a heavy bloom or hard-to-thin varieties (or both), use the high rate, if either of those is not fully true or you have freeze damage, consider backing off the rate a bit. You should also use NEWA’s apple carbohydrate thinning model to evaluate the effect of weather conditions on thinning effect, but the cool weather overall- even after it warms up to the low 70s this week- means thinning chemicals will be less effective and heavier rates should be used. The good thing is, we can try again next week as out fruit approach the ideal thinning window of 8-12 mm and the 6-BA thinners are more effective.

Cool weather means that blossom infection from fire blight does not look to be a concern this week.

Insect activity has been quiet this season, in no small part likely slowed by the cool temperatures. If you don’t have codling moth traps up yet, it would be good to get them up asap and check daily to record the biofix date from which to start calculating degree days until egg hatch. If you need traps, it would be best to order from Great Lakes IPM immediately, as my stock is out. A quick video of me setting a codling moth trap can be found at: https://www.youtube.com/watch?v=OIr_X3hLoQM.

But the warmer weather this week will encourage plum curculio to move into orchards from bordering hedgerows, and they will feed on and oviposit into fruit as they approach ~10 mm in diameter. It is standard practice to mow flowering weeds at 100% petal fall before applying pesticides to avoid attracting pollinators into sprayed areas then to apply a general insecticide to manage plum curculio, European apple sawfly, and some of the lepidopteran pests. Commonly-used materials include Actara, Avaunt, Imidan, and Verdepryn. See the New England Tree Fruit Management Guide for material suggestions.

Keep managing for scab, we’re not done yet and the less-than-promised rains have given sometimes marginal infection periods in the past week. Just stay covered for the time being.

Reach out if you have any questions. tbradsha or (802)922-2591 (cell).

Where trade names or commercial products are used for identification, no discrimination is intended and no endorsement is implied. Always read the label before using any pesticide. The label is the legal document for the product use. Disregard any information in this message if it is in conflict with the label.

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

UVM Extension helps individuals and communities put research-based knowledge to work. University of Vermont Extension, and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status.

Trees at the UVM orchard in South Burlington are at early to late pink bud stage and we expect bloom to start this coming week. This is go-time for setting the crop for 2024, and there are a lot of considerations to take into account as we make management decisions.

First- pest management. This looks like a doozy of a week for apple scab, so stay covered and plan to include both a protectant (mancozeb or captan) and a single site (FRAC groups 3,7,9,11, always rotating between them) fungicide (opens to spray table in New England Tree Fruit guide) in any sprays. This will help with postinfection action for missed apple scab infections as well as help out with cedar apple rust and powdery mildew. Organic growers, I would be applying sulfur with every ½ to 1 inches of rain- you have both washoff and rapid leaf expansion working against you. Today and tomorrow look great for reapplying any sketchy coverage before the next rains come Wednesday and Thursday. The good news on the disease front is that, for now, fire blight is a non-issue as the cool weather hasn’t allowed sufficient bacteria to multiply to make for an infective dose once blooms do open. Keep an eye on NEWA, though, as conditions can rapidly change with just a few warm / hot days.

Insect activity is pretty quiet. We have caught a few tarnished plant bugs at the UVM orchard, and have just hung European apple sawfly, obliquebanded leafroller, and codling moth traps. This is a good time to get those up. As we approach bloom, it is best to keep the insecticides on the shelf to protect both managed and wild pollinators.

Most orchards that were frost affected last year have abundant fruit buds. But look carefully and methodically in your orchards, especially across varied topography, as the cold snap on April 25-26 appears to have done a bit of damage. I am seeing everything from complete bud kill to undamaged buds in the same block. Here is a quick video I made in the UVM orchard of the damage we’re seeing: https://www.youtube.com/watch?v=TPn0s_klGPI

Normally I would be suggesting that folks start thinning at bloom with a mild thinner, but I do suggest a good scout of your buds to see if you have significant damage first. I am inclusion longtime UMASS thinning expert Duane Greene’s recommendations for bloom thinning this year from the Healthy Fruit newsletter (always worth the cost of the subscription, which can be found here):

Chemical thinning suggestions for bloom-time (Duane Greene)

• Weather during the chemical thinning season has been widely unpredictable the fast few years. Given this uncertainty it seems prudent to take advantage of each opportunity to thin with the hope that an application or two will be followed by favorable weather to thin. Even if the weather may not be ideal, chemical thinner applications may predispose fruit to drop following subsequent applications. Given this fact we suggest that you take advantage of applying a thinner at each stage of development, especially early. Apples are less susceptible to hormone type thinners at bloom, so the risk of over-thinning is extremely small.

• We experienced an extremely challenging growing season last year and there may be repercussions from that, which may require special attention. Some blocks of trees were damaged last year immediately following bloom which resulted in trees having few or no seeds. Seeds inhibit flower bud formation for the following year. On these trees and on trees that carried a light crop last year we have noted exceptionally good return bloom which will require special attention to thinning. If nearly all spurs have flowers, it will be almost impossible to thin these trees down to an appropriate crop load using only our usual post-bloom hormone thinners. In these special cases it may be appropriate to apply the blossom thinner ATS at bloom at 2.5 to 3%. Cornell recommends 2 applications with the first being made at 60% bloom. (You can also use the Pollen Tube Growth Model on NEWA, however, that is considerably more involved.) There may be some phytotoxicity but this injury does not last long. Normal hormone thinner applications should probably follow based upon observation of initial set. (Note that use of ATS should be recorded as a fertilizer application in your spray records.)

• Generally, an orchardist chooses to use a hormone type thinner at bloom, especially NAA (Fruitone-L, Pomaxa, Refine) or Amid-Thin. I would like to emphasize again that thinners applied at bloom are at least 50% less effective than when applied post-petal fall. I have never over-thinned any apple tree with a bloom application of a hormone thinner, but I think that this application is necessary to start the thinning process. I have noted that thinner application at bloom may not thin by itself but if followed by a thinner application at petal fall or even at the 10 mm stage greater thinning has been noted on tress that also received a bloom spray.

-NAA is often the default thinner selected for the bloom application. Check the production guide for recommendations for a specific varieties that you are thinning. A 10 ppm rate is often standard when applied at bloom.

-An equally viable choice for a bloom thinner is Amid-Thin, although it is less frequently used. Amid-Thin is a mild thinner and over-thinning is very unlikely. The Amid-Thin label has been changed and updated for the 2024 thinning season. In general, higher rates of application are allowed. We suggest that you read the new label. The application rates suggested for specific varieties have been revised and modern varieties have been included. The highest suggested rate of application remains at 8 oz/100 gallons, although higher rates are now allowed. The maximum amount that can be applied in a single application is 20.9 oz with a maximum amount that can be applied in one year cannot exceed 62.7 oz per acre. In previous years I have added a surfactant (Regulaid) to Amid-Thin to improve thinning capability, but this addition did not have a measurable effect on thinning. Since my experience with Amid-Thin is that it is a mild thinner, I would not hesitate to increase the rate applied a little above 8 oz/100 gallons on harder to thin varieties. Proceed cautiously.

Pest and Pollinator Showcases this week:

Orchard Pests and Pollinators On-Farm Meetings – two locations.

Thursday May 9, 4:30-7:00, Sweetland Farm, 97 Kerwin Hill Road, Norwich, VT

Friday May 10, 4:30-7:00, UVM Catamount Farm, 65 Green Mountain Drive, S. Burlington, VT

These are free, hands-on field meetings to increase your identification skills and understanding of common orchard pests, wild pollinators, beneficial insect habitat in tree fruit production. Pesticide applicator (2) and Certified Crop Adviser (2) credits available.

Questions? Laura.o.johnson or 802-656-4827

Where trade names or commercial products are used for identification, no discrimination is intended and no endorsement is implied. Always read the label before using any pesticide. The label is the legal document for the product use. Disregard any information in this message if it is in conflict with the label.

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

UVM Extension helps individuals and communities put research-based knowledge to work. University of Vermont Extension, and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status.

2024-pollinator-showcase (003).pdf