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.

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.

Video from the orchard this week: https://youtu.be/P1K7XWlg35M

Champlain Valley and other warm site orchards are approaching full petal fall, so there are a lot of decisions to make in the days ahead. Hopefully everyone with any hint of risk for fire blight treated sometime late last week or over the weekend, orchards in bloom may consider treating given this heat spell that’s about to pop up. Everyone also needs to keep an eye out for blossom blight symptoms, and for the shoot blight that will follow. Growers can apply prohexdione calcium (UMASS factsheet, Apogee label, or Kudos label, 6-12 ounces per 100 gallons dilute**) any time now to reduce shoot blight incidence. The plant growth regulator does not affect the bacteria that causes fire blight, it only reduces susceptibility of shoots to infection by thickening cell walls. Treatments will reduce shoot elongation and thicken cell walls for about 2-4 weeks post-application, so retreatment may be necessary every 1-4 weeks until terminal bud set.

In light of the heat that we’re experiencing in the next couple of days, if you can avoid spraying anything (streptomycin excepted) when the weather is >85°, that’s a good thing. Then again, don’t ignore the very real threat of the following pests that need to be protected against.

We are approaching the end of apple scab season, but don’t relax just yet. NEWA is predicting that all spores are mature in warm sites and will all be released with the next decent rain, but the model can lag behind biology. I recommend maintaining coverage for the next couple of weeks. For cooler inland and upland sites, there are likely still spores remaining on the overwintering bank, so stay covered and consider using a kickback material from FRAC class 3,7,9, or 11 if you have any question about residue heading into an infection period which we may see mid-week. As far as materials, everyone should plan on phasing out mancozeb soon, as it it toxic to beneficial predatory mites that do some great biological control or European red mite and two-spotted spider mite, and we’ll soon have to be thinking about its 77-day preharvest interval. Organic growers, I would apply sulfur before and after the rain event, and maybe consider lime sulfur (LS) for the second spray to provide some post-infection control. LS is caustic, nasty stuff, so use it wisely, wear all the appropriate gear, and wash everything down well as it is very corrosive to steel and other materials.

If you’re at total petal fall, then it’s time to start thinking about insect pests, especially plum curculio (PC). PC love this heat and will be ready to oviposit on fruit as they reach 7-10 mm diameter. Organic growers should plan on getting a coating or Surround on trees ASAP, and maintaining that coverage for about 400 degree days (base 50°F) after petal fall (NEWA has a good model for this). This is a longer window of coverage than for non-organic orchard management (308 dd base 50°F), because Surround does not kill the insects and so must be maintained longer until the biological urge to oviposit has completely subsided. For non-organic orchards, effective materials include Imidan, Actara, Avaunt, Voliam, and Agri-Flex. Carbaryl, if used for thinning (see below), will have some efficacy, but probably shouldn’t be your primary material of choice given the weather that is very conducive to PC activity. Thinning rates of carbaryl are about half the insecticide rate, and I would plan on using just that lower rate as a thinner and use a separate material for my insect management. Any of these materials will help to manage the other petal fall insects, including European apple sawfly and the various lepidopterans (obliquebanded leafroller, Oriental fruit moth, codling moth, etc.) that may be emerging at this time.

Thinning. Okay, this is always a tricky one. First, anything applied in the next 40 hours will be highly active because of the heat, so I’d err on lower rates and a lighter touch. A second application may be needed after this weather breaks. Now, I haven’t been in orchards all across the state, but where I have seen bloom from Connecticut valley, Addison county, and our own orchard in South Burlington, it was good to downright heavy. Pollination and fertilization conditions have been good, so I’d expect trees to need a decent thinning this year. The wild card is how much damage orchards may have seen from the April 25 freeze when many trees were at tight cluster bud stage. We are seeing some damage at the UVM orchard, but there are enough good fruit that are starting to set that I am ready to thin moderately aggressively this season. The New England Tree Fruit Management Guide has some good variety-by-variety recommendations, so I recommend starting there. A good, standard petal fall spray of 1 qt/acre of carbaryl and 8 oz/acre Fruitone N or L (I did the TRV adjustment for you) should do the trick for most orchards. As fruit approach 8-10 mm in size and the weather starts to warm up, the 6-BA thinners will be very active, and they are a great choice for small fruited cultivars (Macoun, Gala, Fuji, Empire). For organic orchards, it’s time to start hand thinning. A lime sulfur spray used for scab can help to knock some fruit off, but it’s not labeled specifically for that use.

I think that covers it for now.

**This reference to amount per 100 gallons dilute refers to Tree Row Volume (TRV), which is a somewhat out-of-vogue method for adjusting spray rates to compensate for canopy volume. I describe it some here, but in simple terms, it calls for measuring the tree canopy volume and estimating the number of gallons of water to saturate the canopy to wetness (dilute gallons per acre, DGA). No one sprays at full dilute, that wastes time, money, and water. For a good rule of thumb, large, standard trees 20 feet tall planted at 30 feet x 40 feet spacing had (notice the past tense) about 420 DGA. A more typical ‘large’ semidwarf orchard on M.7 or similar with 12 foot tall trees planted at 12 ft x 18 ft would have 200 DGA. DGA decreases down to around 100 and stays there pretty consistently for tall spindle and similar high density, narrow-canopy systems. BUT, we often do not recommend reducing TRV below 150, maybe 120 if you have excellent coverage and an easily sprayed canopy. And this TRV is only used to determine the rate of material used per acre, not how much water you put in the tank. So. Let’s just say use 200 DGA for semidwarf trees, 150 for trellised trees. Back to the Apogee example, let’s use 8 ounces per 100 DGA for simplicity’s sake, that would be 16 ounces per acre to the big trees, 12 ounces to the smaller high density trees. Then figure out how much to put in the tank based on the amount of water you spray per acre, which is likely 50 (or less?) to 150 gallons.

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.

We have an accompanying video this week from our vineyard: https://www.youtube.com/watch?v=gzs7Yqm_ZcY

With the heat finally arriving, things are moving fast with vines at the UVM vineyard range from bud burst to 1-5 inches of growth depending on variety and relative vigor. It’s time to really be thinking about protecting vines from early season disease infections. Most cold-climate cultivars will not need disease protection until 5-8” of shoot growth, but any vineyards with heavy disease pressure last year and organic vineyards should begin earlier, especially if inoculum reduction through thorough removal of diseased wood and mummy berries and/or dormant application of lime sulfur was not performed. I still recommend our fact sheet, An Initial Integrated Pest Management (IPM) Strategy for New Cold Climate Winegrape Growers as the best resource to boil the decisions down to a simple ‘prescription’, with the caveat that since it was written some new pest management materials have been released and inoculum may have increased in your vineyards which could lead to increased disease pressure. Growers should have an up-to-date copy of the New England Small Fruit Management Guide (on-line and hard copy versions) and/or New York and Pennsylvania Pest Management Guidelines for Grapes as a reference for specific materials, their efficacy, and use considerations. Remember however that the guidelines are written largely for vinifera and less disease-resistant hybrids, so the specific spray programs recommended may be overkill in Vermont vineyards.

The primary disease of concern at this point is phomopsis, as rachis infection at this point in the season may cause significant fruit loss at harvest. Anthracnose may also be active at this point , given the warm/hot weather are expecting later this week. Vineyards that have had recent problems with those diseases or organic growers using copper or other less-effective materials may consider treating this week; if you haven’t had major problems with those diseases, treatment can wait until the 5-8” growth stage as long as you are using a highly effective contact fungicide like mancozeb or captan. Organic growers are in for a bit more work. The standard fungicides, copper and sulfur, have only fair efficacy against this disease at best.

It is worth noting that both copper and sulfur (including lime sulfur) can cause phytotoxicity on certain cultivars. Dr. Patty McManus summarized her research on copper and sulfur sensitivity in cold-hardy grapes in the 2/8/16 Northern Grapes newsletter, and I’ll summarize it to say that Brianna should receive no copper; and Frontenac (all types), La Crescent, Leon Millot, Marechal Foch, Marquette, and St. Croix should receive no more than 2-3 copper sprays per season. Save those for later when black rot and downy mildew become bigger concerns. Sulfur sensitivity was observed on several cultivars, and its use (including lime sulfur) is discouraged on Foch, Millot, Brianna, and Louise Swenson; with limited (2-3) applications suggested on LaCrescent and St. Croix.

I’d say any time now is good to get your shoots thinned down to 3-6 shoots per foot of canopy. Keep more on more vigorous vines, less on weaker ones.

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.

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