The time has come to hang apple maggot fly (AMF) traps in Vermont orchards. These are some of the easiest pests to manage using an IPM strategy, so there’s really no excuse. The idea is to assess the population in the orchard before applying prophylactic sprays. By using red sticky traps, you can time treatments for best effectiveness, and maybe even skip treatments if the populations are low enough. Traps are red plastic balls that you coat with Tanglefoot adhesive. Kits including traps and adhesive are available from Gemplers and Great Lakes IPM. We have some available from our program as well, if you want to swing by South Burlington. If you want to come by for traps, please email me and we’ll be sure to have some ready.

AMF traps should be hung at least four per 10-acre block, preferably at the orchard perimeter and especially near sources of the insect, like wild or unmanaged apples. (Video here: Vermont Apple IPM: Hanging apple maggot fly traps.) Placement in the tree should be about head-height, and surrounding foliage should be trimmed away- this trap is largely visual, and you should be able to see it from 10-20 yards away. The traps may be baited with an apple essence lure that improves their attractiveness dramatically. When using traps to monitor AMF populations to time sprays, unbaited traps that catch one fly per block (as an average of all the traps in the block) would warrant treatment; the lure makes them much more attractive such that you can wait until an average of five flies per trap are caught before treating. For most growers, the main insecticide used against AMF is Assail, Imidan also works but it has a long reentry interval and tends to leave visible residue on fruit. For organic growers, Surround works well, but its use in midsummer may increase European red mites, and it can be hard to remove at harvest; spinosad (Entrust) works pretty well too. First AMF treatment is still a few weeks off, most likely.

It is summer lepidoptera season, and monitoring and treatment should be on everyone’s minds, especially for codling moth (CM) and obliquebanded leafroller (OBLR). CM are active and eggs are likely still hatching across the state, so growers who have caught CM in their traps or who often have issues with this pest (that’s most everyone) should apply something effective against them at the appropriate time. Most orchards saw CM first trap captures in late May and peak at the beginning of June. Optimum spray timing for CM is 250 degree days (base 50°) after first catch with a follow up spray 10-14 days later. Very specific materials like insect growth regulators (Intrepid, Rimon) or granulosis virus (Madex, Cyd-X) can be used that are very safe to non-target insects. One or two applications of a material should suffice for first generation.

OBLR are just showing up in traps but generally at low levels compared to previous years, and treatment should be timed at 360 degree days (base 43°F) after first catch. There is a NEWA model for this pest, and a material like Bt (Dipel, etc.) is effective (but not against CM). Other good materials targeted at this lepidopteran pest include Intrepid, Rimon, Delegate, and Belt.

I have seen one pretty bad case of European red mites already, and hot, dry weather is also conducive to mite flare-ups. A weekly or, if the numbers indicate, bi-weekly scouting will help to indicate if there are high enough mite numbers to consider treatment. Information on monitoring: https://netreefruit.org/apples/insects/mites. Mites should be treated based on the following thresholds: in June, 1-2 mites per leaf; July, 5 mites per leaf; in August, trees are more tolerant of feeding so treatment should only be applied if there are over 7.5 mites per leaf.

Diseases: keep checking on your scab, if you have none (I mean none), then it’s okay to relax. That said, the summer diseases sooty blotch and flyspeck are of concern now, but they require 270 hours of leaf wetness for lesions to form, so fungicide coverage between that period should be maintained. I am also seeing more leaf spot diseases (here’s a great article on the different leaf spots you may encounter) this year that may warrant continued coverage to reduce potential defoliation and/or spread to fruit rots. Recommendations from our colleagues at Cornell suggest including a FRAC group 3, 7, or 11 fungicide with your captan cover to reduce incidence of these diseases. Keep in mind that one inch of rain washes off half of your coverage, after two inches, it’s gone.

It’s time to wrap up any ground-applied nitrogen fertilizers, but potassium and magnesium fertilizers can be applied any time in summer. It’s also a good idea to start your regular foliar calcium sprays, especially on bitter pit-prone cultivars like Honeycrisp and Cortland.

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.

This will be a fairly brief newsletter today as I am away all week at a conference in Chicago. Feel free to e-mail or text me if you have specific questions, I will keep up the best that I can. -TB

We are entering into what I consider early summer insect management season. The main insect of concern at this point is codling moth, although plum curculio may still be active in some orchards. Two times sprays against codling moth, pheromone baited wing traps would have been hung prior to bloom and the date of first sustained capture recorded. From that point degree days are calculated using a base of 50°F and hatching larvae are best treated when 220° days have accumulated. For the UV orchard where we had sustained moth capture on May 17th, that would put us at good timing to manage our first generation of codling moth this week. Our orchard has a relatively high population and this emergence is earlier than I have seen in other orchards in the region, so your site may be able to be treated next week in the Champlain Valley or even later in the cooler inland orchards. Cottonmouth should best be managed with a material that specifically has high efficacy against that particular pest. Some good options are presented in this table Apple Insecticide Efficacy : New England Tree Fruit Management Guide : UMass Amherst (best seen on a computer or tablet screen, it doesn’t render well on a smaller phone screen).

Even though primary apple scab season is done for virtually all orchards in the state, I still recommend applying at least 1/2 rate of captan as we continue to have wet weather and some are diseases and fruit rots can get out of control if not managed. This is also the time to be applying calcium in every spray, especially on Honeycrisp.

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.

Passing this on from Bethany again. -TB

Hi there again folks,

I’m writing in to you on the eve of the most important disease prevention period of our grape systems! Over the past two weeks we have had several Phomopsis and black rot infection events according to our NEWA models. As we enter pre-bloom it is essential that we are using our most powerful disease prevention and suppression tools against black rot, Phomopsis, and maybe even powdery mildew in vineyards where this is a particular concern.

Part of why there have been so many infection events is because we are experiencing so much rain. Both Phomopsis and black rot infections are spread by rain splash and are encouraged by humid and warm temperatures over 60 degrees. While we can’t do much about the weather, other management strategies will include:

Cultural methods (EXTREEMELY important for organic growers)

• Making sure you’ve thinned shoots! By removing excess plant material you not only better balance the vine, but also allow for better spray penetration and airflow both now and into the summer months.
• Remove any woody material that has not flushed out by now. This material will act as a disease reservoir if not removed promptly. It is worth taking a walk through the vineyard to find what you may have missed

Chemical Methods

• Check available NEWA models to track possible infection periods. The model uses climatic data such as rainfall, temperature, and hours of leaf wetness to predict infection events. Be sure to enter the shoot stage and use the closest station to you for the most accurate predictions. Contact Terry if you are interested in hosting a station!
• Because pre- and post- bloom is THE MOST IMPORTANT infection window for diseases such as black rot and powdery mildew we should all be applying our best and most reliable materials. Recs from Terry: “Every vineyard should be covered with the full suite of disease management products this week. That means mancozeb or captan plus a DMI, SDHI, or strobilurin (group 3, 7, or 11, respectively) material for non-organic vineyards; and sulfur plus copper (watch for incompatibilities on certain varieties, page 9 here) on organic vineyards. This would also be a good time to add biologicals, since we’re at ‘all hands on deck’ right now. Some materials, like Lifegard and Howler, are systemic acquired resistance promoters and need to go on a few days prior to infection. Others, like Serenade and Double Nickel, are biological extracts but can be mixed with other materials. Either way, these applications should be made a before infection, so spraying in the next day or two is a good idea.”

That’s all for now- I myself have to prep for a spray tomorrow. I will be in touch soon to introduce our good friend Downy Mildew and talk about weed and canopy management!

Signing off,

Bethany Pelletier & UVM Fruit Lab

__

Terence Bradshaw (he/him)
Associate Professor, Specialty Crops

Chair, Dept of Agriculture, Landscape, and Environment
(formerly 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

UVM Commercial Horticulture | UVM Fruit Blog
Horticulture Research and Education Center
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Orchard video covering this week’s material is here: YouTube 5/30/2025

Vermont orchard are at petal fall (inland and upland) to generally 10-12 mm fruit size in the lower elevation valleys. Primary apple scab ascospore release is complete for all orchards, so apple scab is not a major management consideration only if you know the disease is managed well in your orchard. That means taking a very careful, methodical walk through the orchard and checking high up in trees and at the ends of rows where coverage may have been spotty to ensure that you don’t have active scab in your orchard. I recommend keeping at least some captan on for the next week or so anyway, and adding a single-site fungicide material if you have questions about your spray efficacy and go into tomorrow’s rains without appropriate coverage.

If you applied full-orchard petal fall insecticide, you are likely between insect pests now. Codling moth still needs some time for mating females to lay eggs and eggs to hatch. For more information on ecological codling moth management, consider attending this Cornell Zoom meeting on the topic next Tuesday June 3 at 2:00 PM. Plum curculio will still be active in orchards for another week or two, but if you applied a block-wide insecticide at petal fall, you can manage PC with boerder row sprays.

The main management consideration that I am getting a lot of calls and emails about is thinning. The crop is all over the place, from well-thinned single fruitlets; to unthinned six-fruit clusters with intact king fruit; to unthinned clusters with no king fruit as king blooms were open during the wettest, coldest, most bee-unfriendly weather of the spring. Fruitlet size also runs the gamut from petal fall (~5 mm) to up to 15-20 mm.

Thinning is complicated, but it needs to be done. Dr. Renae Moran has a good summary of chemical thinning materials and strategies in the New England Tree Fruit Management Guide: Apple Fruit Thinning : New England Tree Fruit Management Guide : UMass Amherst. I’ll post some general thoughts in bullet point:

• Fruitlets whose sepals have not closed and/or whose stems have begun to yellow are likely to thin off.
• Fruitlets will be most susceptible to the older thinners (NAA, NAD, 6BA) at 10-12 mm in size. Carbaryl at 1 pint per acre increases their activity, and I suggest including it if using those materials.
• Once fruitlets are over 18 mm those thinners no longer work sufficiently to warrant their application. A newer material, Accede, is available and labeled in Vermont for thinning apples and peaches. It is much more preferable to the old ‘rescue thinning’ standby, Ethephon (which I would no longer recommend now that there is something netter on the market).
• Thinners are more effective when warmer / hotter weather comes before (2 days) or especially after (4 days)n application.

It’s hard to make blanket recommendations across multiple sites, elevations, fruit set levels, cultivar, tree ages, and all the other interacting aspects that we see across the state, so I won’t even try. If you have a specific scenario you’d like to run by me, reach out and I’ll do my best to help. My plan for our UVM orchard is to go in Sunday or Monday with 1 pint per acre of carbaryl and 100 ppm of Maxcel.

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.

This was meant to be sent out with some field pictures yesterday morning, but my teaching job and administrative duties all collided into a backup of worktodo this week. Hopefully it’s timely enough to be useful. -TB

After a few decent days of pollination during bloom last week in between the cold, cloudy, showery weather, I saw good fruit set on most cultivars at the UVM orchard over the weekend. Short of measuring and tracking the diameters of individual fruitlets to those which are continuing to grow, a very effective way to see if a fruit has been set is to look at the sepals on the calyx end of the fruit which were at the base of the blossoms when it was a flower. These five pointed, modified leaves will close up a bit on a blossom that was pollinated, fertilized, and is developing into a fruit.

Management considerations at petal fall are a bit more difficult than usual given the relatively low blossom density we had this year after substantial crops around most of the state last fall, questionable pollination weather for much of the bloom period, and continued cloudy, cool wet conditions. All of these would suggest that growers should be cautious with applying thinner applications this year. However, in most situations aside from an off-year on biennial cultivars or orchards with very poor fruit set, I recommend application thinning this year (and really every year). The weather this week is not conducive to application thinners that increase cell division, e.g. MaxCel, Exilis, etc. Those materials should be left on the shelf until temperatures after application will hit 75 to 80°F. That leaves the auxin-based thinners (Fruitone, Refine, etc.) as the best option for thinning the crop at petal fall. That said, even those materials do not work well in these 50° temperatures. Fruit are also growing extremely slowly, and will remain at the ~5mm “petal fall” window through the weekend. This will allow us to wait a bit until warmer weather is expected and will also allow late blooms to drop and minimize pollinator exposure to sprays. Dr. Terence Robinson from Cornell recently recommended relying a bit more on cabaryl to increase thinner activity this year. Where there is complete pedal drop and wildflowers have been mowed or otherwise controls, I recommend addition of carbaryl (Sevin XLR alone or generic carbaryl plus a surfactant) at one pint per acre, which will help to increase the effectiveness of thinning materials. Carbaryl is a relatively mild insecticide, but will provide some protection against insect pests that have had free reign of the orchard in the last few weeks if used at two pints per acre. I do recommend getting in with a more effective fall insecticide as soon as you are able for control of plum curculio, European apple sawfly, and some of the generalist lepidopteran pests that I have observed in various orchards. Codling moth have just begun to be trapped in area orchards, which means they are still flying and mating, and therefore have not laid eggs nor those eggs hatched into a stage where a targeted pesticide would be most effective. We will likely manage those pets next couple of weeks.

For most Vermont orchards, the apple scab ascospore maturity model predicts that all overwintering inoculum has been released and if the disease adequately controlled during the primary phase of the disease, then management for that best may be finished for the 2025 year. However, I strongly recommend maintaining fungicide coverage for the next 10 to 14 days. That is because apple scab is not the only disease of concern. Some of the summer fruit rots can get established early in the season, cedar apple is likely still a consideration, and in the case of low spray orchards or orchards where protection completely washed off, Marssonina leaf spot could become a serious disease given the constant wet weather we are seeing. We also cannot know that we have fully controlled for apple scab until we give enough time to see any lesions that may have broken through during these long infection periods.

Fire blight may not be a huge consideration this year, unless you had open blossoms that were not covered with streptomycin during the potential infection that occurred on Friday and / or Saturday of last week. The temperatures are just too cool now the bacteria to build to an infective population, and most orchards are at petal fall anyway which means that blossoms are no longer susceptible to the disease. Keep an eye out in the coming weeks for the development of any potential blossom or shoot blight symptoms. In orchards that have had a history of fire blight, I recommend maintaining low dose prohexadione calcium (Apogee, Kudos, etc.) applications for the next several weeks to help stiffen up cell walls in developing shoes and which will reduce the trees susceptibility to fireplace shoot infection.

Here’s what we’re doing for pest management and thinning in the UVM orchards this week: fungicide (captan plus Rally) tomorrow Wednesday morning to provide coverage through the next round of wetting on Thursday and Friday, then a weekend application of carbaryl plus eight ounces of NAA per acre for thinning, Avaunt insecticide for curculio and other petal fall pests, and possibly another fungicide depending on how much rain fell since the last application. That thinning application will be timed to coincide with the necessary low wind conditions and hopefully just ahead of any expected warm up we get early next week.

Good luck and let me know if you have any questions.

Terry

—

Terence Bradshaw

Associate Professor and Chair

UVM Agriculture, Landscape, and Environment

Sent via mobile app. Please excuse typos.

__

Terence Bradshaw (he/him)
Associate Professor, Specialty Crops

Chair, Dept of Agriculture, Landscape, and Environment
(formerly 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

UVM Commercial Horticulture | UVM Fruit Blog
Horticulture Research and Education Center
Message me on Teams

UVM’s Our Common Ground Values:
Respect | Integrity | Innovation | Openness | Justice | Responsibility

UVM is subject to the Vermont Public Records Act and communications to and from this email address, including attachments, are subject to disclosure unless exempted under the Act or otherwise applicable law.

With welcome, warm, sunny weather, we are seeing epiphytic infection potential rise in virtually all orchards around the state. We are expecting by Thursday or Friday to have high enough populations of bacteria to cause fire blight infections on trees with open blossoms. That will include most orchards in the state which may either be just beginning to bloom or starting to end their bloom. Growers should plan to apply streptomycin to all blooming orchards on Thursday or Friday this week. Streptomycin works best when applied with a non ionic surfactant. There is also good potential for apple scab infection this weekend, so application of an appropriate fungicide would also be prudent. Next week we’ll discuss options for insect management and thinning at petal fall.

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.

As I write this just after noon on Saturday, May 10, it looks like this long stretch of rain we have been experiencing for the past week is wrapping up a bit earlier than expected. Over the past seven to ten days around the state we have seen rainfall totals from less than two to over five inches, and rain or at least drizzly conditions every day. Even when there were gaps in the rain, apple scab spore germination can continue in dry periods under 24 hours, so for most orchards there has been essentially a continuous scab infection since May 1 or 2. Many growers have sprayed twice during this infection, but we can expect for most orchards that fungicide residue sprays applied even yesterday morning may be considered gone or at least substantially compromised. I recommend that growers go in with an appropriate kickback material as soon as possible now that the rain has largely stopped, looks like it will stay stopped, and wind conditions for spraying look good through Monday. Post infection activity starts from the time of application, so delaying application for a day or two will reduce the time period that the material will be active on spores that germinated in the past couple of days. The materials that have kickback activity fall in the FRAC codes 3, 7, 9, and 11. The strobilurin materials in FRAC code 11 tend to have less kickback activity and are more useful for summer diseases so I do not recommend those be used at this time. The DMI fungicides in FRAC code 3 tend to have longer kickback activity as well as have excellent activity against powdery mildew and cedar apple rust which are also active at this time. As always, I recommend tank mixing single site fungicides with a protectant fungicide like mancozebs or captan. We are approaching the end of the season for using mancozeb fungicides if applying at the full label rate of 6 lbs per acre. Captan is another effective fungicide that many growers tend to switch to at this time of year.

As orchards in the warmer parts of the state are in full bloom, and insect activity has been very low statewide with little to no European apple sawfly observed on traps in multiple orchards, I do not recommend application of insecticides at this time. Warm weather is expected to return on Monday and with it we should finally see substantial pollinator activity. There is a lot of concern around the state right now that the weather conditions in the past week have been inadequate for appropriate pollination of fruit crops, but I expect that a warm sunny day on Monday will provide adequate pollination for most orchards that are in bloom.

When we think of a blooming orchard we also think about fire blight. Conditions have been so cool during and prior to bloom that the epiphytic infection potential of the bacteria that causes the disease has been very low to such a point that treating blossoms has not been recommended. At the far end of the NEWA fire blight model five days out some orchards are showing an EIP of over 100, which could cause infection if all other conditions are met. You will need to revisit this later in the week, and I recommend that all orchards have a treatment of streptomycin on hand to use should an infection period be predicted.

Speaking of bloom, we have observed in multiple orchards relatively low blossom density this year. The frost that affected most orchards in 2023 allowed trees to save resources they would have put into growing crops that year which produced a large bloom last year. That heavy bloom event and resulting large fruit crop taxed the resources on many trees especially on varieties that lend themselves toward biennialism like Honeycrisp, which resulted in a lower density of fruit buds this year. There is nothing you can do to put fruit buds on a tree that doesn’t have them for this season, the best you can do is thin aggressively in those heavy blooming years. I guess most orchards will have to think about that next year. That doesn’t mean that I don’t recommend thinning crops this year, we’ll discuss that in the next newsletter.

__

Terence Bradshaw (he/him)
Associate Professor, Specialty Crops

Chair, Dept of Agriculture, Landscape, and Environment
(formerly 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

UVM Commercial Horticulture | UVM Fruit Blog
Horticulture Research and Education Center
Message me on Teams

UVM’s Our Common Ground Values:
Respect | Integrity | Innovation | Openness | Justice | Responsibility

UVM is subject to the Vermont Public Records Act and communications to and from this email address, including attachments, are subject to disclosure unless exempted under the Act or otherwise applicable law.

Reminder: TREE FRUIT TWILIGHT MEETINGS
Thursday and Friday, May 8 and 9, 4:00-6:00 pm

Join the Vermont Tree Fruit Growers Association and UVM Extension on May 8 at Yates Family Orchard, 1074 Davis Road, Hinesburg, VT or May 9 at Wellwood Orchard at 529 Wellwood Orchards Road, Springfield, VT. Topics discussed include tree fruit management practices, value added products, marketing, pest and disease updates, pollinators, and funding opportunities and challenges. The events are free and geared to commercial growers and people that work with them, and offer one VT pesticide recertification training credit for categories 1A, 1, 2, 3, 4, 5, and 6. Registration is not required, but helpful for any unexpected announcements regarding the meetings. To let us know if you plan to attend, contact Laura Johnson at laura.o.johnson or 802-656-4827.

We are in full scab management season with ascospore maturity creeping up, and significant, extended wetting that can discharge a lot of spores. Hours required for infection to occur are relatively low with the temperatures in the 50s and 60s that we are seeing this week. Fungicide coverage should be maintained during this wet week, and a material with kick-back activity (FRAC codes 3, 7, 9, 11- be sure to rotate among these!) applied should you have any question on coverage of protectant fungicides. Use of these materials should help with management of other diseases, including powdery mildew and cedar apple rust, as well.

For the time being, I’m fairly confident that we can consider fire blight a non-issue heading into bloom. That can change quickly should things warm up, and trees are susceptible to blossom blight any time blooms are open. The number to watch for in the NEWA fire blight model is the value in the “Infection Potential EIP value” column (data shown for UVM Horticulture Research and Education Center in South Burlington, VT):

That number refers to the Epiphytic Infection Potential, a relative value that predicts the size of the population of the Erwinia amylovera bacteria that causes fire blight infection. When that number reaches 100 the population is considered large enough to cause disease infection. That number is affected by accumulated heat units, so cool conditions cause it to decrease, whereas hot weather can rapidly cause bacteria to multiply rapidly, The other conditions that are included in the model include wetting events, temperature during bloom, and presence of open blossoms. The EIP values predicted for the next five days are just too low for fire blight to be of concern. This carries across all parts of the state, although southern Vermont orchards are seeing or expecting warmer temperatures that check the “average 60°F during bloom” box which makes the relative risk higher (i.e., yellow flagged). But keep an eye on that EIP number – if it’s well under 100, you’re likely in good shape.

Insect management should be on your mind, though. Many growers know that I am generally not in favor of insecticide sprays at pink unless scouting indicates a need because of the residues that would be present for pollinators to be exposed to at bloom, but this is a great time to be monitoring pest populations to be prepared to manage them when the time comes. I checked white sticky traps hung on 4/24 for European apple sawfly and found none, same for codling moth traps hung last week. For those who are following along, we use this monitoring summary to plan our trapping. In addition to codling mothy and obliquebanded leafroller listed there, we are also trapping for Oriental fruit mothy and dogwood borer, both traps can go up now. For the latter pest, my M.S. student Eli Wilson wrote a summary on them a couple of years ago:

Here is what you need to know about the dogwood borer (DWB):

Identification:

The adult form of the dogwood borer is a small, clearwing moth that is shown in the image below. They have approximately a 1-inch wingspan and have a black and yellow color pattern making them resemble wasp. They have mostly clear wings with circular windows at the tips. The larvae of the dogwood borer (DWB) are about ½ inch long and can range from white to light pink with a large brown head.

This is the time of year that the adult dogwood borers begin laying their eggs in the crevices of tree bark, so it is important to be monitoring for their presence in your orchard.

Damage:

The dogwood borer larvae are the ones that cause the damage, feeding on the phloem and cambium layers of the tree. Signs of an infestation may first appear as a pile brownish red frass on the outside of an entry hole in the tree trunk. While a few borers will not cause significant damage a population can build over the years and lead to reduce tree vigor and even girdling. An image of the larval form of the dogwood borer (DWB) is also shown below.

Trapping:

You will be using two orange TRÉCÉ PHEROCON VI DELTA TRAPs to monitor the dogwood borer in conjunction with lures labeled “DWB”. The lures should be replaced every 4 weeks and you can replace the stick liners every week if you choose. If you do not replace the liners each week, be sure to remove all the trapped dogwood borers after recording that week’s catch total. The orange Delta Traps should be hung within the tree canopy at approximately 4-feet off the ground as shown in this instructional video: Hanging Delta Traps

I hope this information is helpful, if you have any questions, comments, or concerns please feel free to reach out!

Happy trapping!

Best,

Eli Wilson

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.

PAT credit listed 2025-spring-tree-fruit-twilight-meeting.pdf

This edition of our newsletter was written by UVM PhD student Bethany Pelletier. You can expect more from her this season. While I have you, I’d like to promote the Cold Climate Viticulture course Bethany and I will be teaching at UVM this summer. We haven’t finalized this year’s syllabus, but you can see the 2023 syllabus here. This course is only offered in alternate years, so will not be available again until 2027. Please reach out to me if you have any specific questions about it.-TB

Spring has sprung in Burlington Vermont! Here in South Burlington, some of our earliest varieties like Marquette and Foch are looking pretty close to bud burst. Here are some things we should all be thinking about around this exciting time of year;

Our first line of defense for ALL growers is going to be good pruning and sanitation techniques. We should all be just about pruned up by now, but it’s never a bad idea to do another vineyard walk and make sure you didn’t miss a vine or two. Taking the extra time to clear out any dead wood or at least flail mow to break it apart will make a HUGE difference in the presence of our early season fungal pathogens like black rot and Phomopsis. Be sure to discard this material far away from the vineyard, not just at the end of a row.

As buds reach 1-2” height it will be time to shoot thin. We want to take it down to 3-6 shoots per foot of canopy, ideally keeping the primary shoots where possible. Many of our cold climate varieties like to push out their secondary shoots alongside the primaries (as pictured below, the primary is the larger shoot coming out at an angle). We should try to favor the primary shoots as they will have more flowers and generally develop into a stronger cane. This is also the best time to flick off any buds coming up on the trunk that we don’t want for future replacements, as these can REALLY gum up the airflow of the canopy. Shoot thinning is another IPM tactic that will make a huge difference in your disease defense regardless of your pesticide strategy. A cramped and crowded canopy will make a dark and humid microclimate, encouraging more mildews later in the season. In addition, more shoots will mean far more labor for you down the road when it comes time to shoot thin; much more pleasant to knock some shoots down while they’re still young and small!

UW Fruit Program

While proper pruning, sanitation, and shoot thinning will always be your first line of defense in the vineyard, we should all still be thinking about our pesticide management plan for the season. Pesticide orders should be placed by now, and spray equipment cleaned and calibrated. For all growers, but in particular those that use live biopesticides, be sure to check expiration and efficacy dates on your materials. Biopesticides and many organic pesticides often should be replaced yearly for maximum efficacy.

For the first time in my years as a student at UVM I am seeing some notable numbers of flea beetles. I’ll attach a picture here, they may look familiar to you already!

Tom Zabadal. MSU College of Agriculture

I am not too concerned about these at the moment, given that bud swell is progressing fairly rapidly so these little guys will only have a few more days to get any bites in. But if for whatever reason our bud development stalls out, we may want to consider some sort of control. If this happens to any of y’all please poke our fruit team for some management options.

Now that pruning is over and the vineyard is looking nice and neat, it can be easy to forget just how essential these early weeks are for disease prevention. Cold climate cultivars are typically not in need of pesticide intervention until about 5-8” of growth. However, if you are an organic grower or had bad early season disease last year you may want to start putting down some protection sooner! In the UVM vineyard we have both conventional areas and ‘organic’, so I am already planning my future sprays. Here are some tried and true suggestions from our own Dr. Bradshaw;

“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.” -T. Bradshaw, 2024

I believe that’s all for now folks! I wish you all the best of luck this growing season, and fingers crossed that this lovely warm weather stays with us through bud break! I’ll be back again soon with disease outlooks and funny stories from our own vineyard.

Best,
Bethany Pelletier & UVM Fruit Lab

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.

Vermont orchards are generally at green tip bud stage for the coolest locations in the state to tight cluster in warmer locations. Apple scab continues to be the primary pest management consideration of concern. I recommend maintaining a protectant fungicide and, given the off and on wetting of the last few days that has likely resulted in an extended infection period for most orchards, a single site fungicide with kickback activity such as those in FRCAC codes 3, 7, 9, or 11 (remember to rotate these chemistries to avoid development of fungicide resistance). Weather for spraying conditions has been all over the place this week with high winds on many days. It seems the best time for extended low wind conditions appears to be Wednesday night through Thursday morning. We are expecting, fairly substantial rainfall on Friday, which should result in the next major infection period.

As we approach bloom, it is important to consider the potential for the development of fire blight. I recommend having one application of streptomycin on hand as we head inro the bloom period. Streptomycin is always best used in conjunction with a degree day based fire blight model. Strep is extremely effective against blossom light infections when applied within 24 hours of infection and where bacteria has not developed resistance to it (and I have not yet seen evidence of strep resistant bacteria in Vermont.) There are other measures that may be taken to reduce reliance on streptomycin or increase its efficacy. Some biological control materials, (e.g., Lifegard, Actigard, Regalia) are labeled as an act as systemic acquired resistance promoters. These materials act like a sort of vaccine that prompts the tree’s immune system to fight off fungal and bacterial infections after application. While the data do not show complete efficacy against devastating diseases like fire blight, recent work (1, 2) done in New York State by Kerik Cox and Anna Wallis shows that they have potential to control blossom and shoot light at levels between a non-treated control and a streptomycin application. Where you may have had fire blight problems in the past, the use of one of these materials prior to bloom (as in this week) may help to reduce disease incident if infection occurs. Unless you are under constraints as an organic grower, I still recommend using streptomycin if the models call for it in your orchard. However, for growers, who have faced substantial fireplace problems in the past, the use of these materials may be affective in helping to get the disease under control in this in future season. The evidence is also good for the efficacy of low-rate(3 oz/acre) prohexadione-calcium (e.g., Apogee, Kudos) applied at pink bud stage followed by four biweekly applications at 2 oz/acre in reducing shoot blight symptoms.

Now is the time to get pheromone baited traps up for monitoring lepidopteran (moth) pests. The one that we monitor for most closely and which most likely drives management decisions is codling moth. Pheromone baited traps should be hung one per acre block and should be located 50 feet or more from each other to reduce the attractive effects from one trap to another. Pheromone capsules are specific to the type of moth that you were trying to catch, so each trap should include only one capsule for only one particular moth. For codling moth, we hang traps prior to bloom and check them daily, especially during warm weather, and record the date of first moth capture. I posted a video to our YouTube channel of me assembling and hanging a CM trap yesterday. That date can be used in the NEWA degree day model to time spray application toward freshly laid eggs or hatching larva. It is this precision of timing and maximizing efficiency of pest control materials that allows growers to use relatively expensive, highly selective (not harmful to most beneficial insects), and worker safe materials in a cost-effective manner. This year at the UVM orchard we are using pheromone traps for codling moth, obliquebanded leafroller, dogwood borer, and oriental fruit moth.

Growers should also be checking European apple sawfly traps that were hung last week and making counts of trapped insects. In some years, EAS may require treatment prior to bloom. We try to avoid the use of any insecticides at this point in the year because wild pollinator populations are increasing and we want to reduce the likelihood of residues that wild and managed honeybee pollinators are exposed to when visiting flowers during bloom. High levels of sawfly could cause substantial fruit damage, especially when bloom, when we are prohibited from using any insecticides, is extended. In the unlikely event that a pre-Bloom insecticide is used, I recommend, a relatively short-lived material such as a pyrethroid, and do not at all recommend the use of neonicotinoid material which have a high likelihood of having toxic residues in pollen and nectar that are collected by pollinators during bloom.

It’s time to really think about getting your nitrogen and other fertilizers on as the trees will be rapidly developing tissues in the coming weeks. If you are using granular fertilizers, I recommend split applications and applying half pre-bloom and the other half in early to mid-June, being sure to complete all nitrogen applications before the end of June to reduce likelihood of winter injury in the following season. If you have not yet it is a good idea to apply boron and zinc foliar fertilizers to strengthen developing blossoms prior to bloom.

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.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. 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.

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.