Grapevines at the UVM Horticulture Research & Education Center are showing up to three to five inches of shoot growth, depending on variety. We are beginning to enter a critical time for disease management- all growers should plan on starting your spray program this week or soon thereafter (for inland growers with less growth). I pretty-well listed the strategies to take last week, so I’ll allow folks to look there.

Now is a good time to get out and clean up the ‘nubs’ left at the ends of spurs after pruning that will die out and serve as reservoirs for phomopsis and other diseases. While you’re at it, this is an especially good time to thin shoots. Cold hardy grapes trained to a high-wire trellis and in good health can support about six shoots per foot of canopy; select the best developing shoots and break off the others now while they are easily breakable with your fingers. Maria Smith and Dr. Michela Centinari at Penn State wrote a good summary of shoot thinning available here. I suggest reading it on the deck this holiday coming weekend with a nice glass of wine, and getting out in the vineyard next week to set this year’s crop on the right track.

As a reminder, all of my older IPM bulletins are archived on the UVM Fruit Blog.

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.

Apple scab is still a concern in Vermont orchards. However, as heat gas continued to accumulate and relatively regular showers have provided for spore release from leaf litter, the supply of inoculum available to infect orchards, assuming you have prevented infection during these wetting events, is dwindling. The NEWA model in some sites shows up to 99% spore discharge by the end of this week, but like all models, we need to be careful as reality on the ground may be off by as much as 10%, which can be enough top cause infection. Bottom line- don’t let your guard down on scab yet, but this does look like an early-ending scab season. Stay covered and we’ll revisit next week.

Normally when we think of a cool / downright cold spell after a warm stretch conducive to fire blight, we consider the risk to decline with the temperatures. However, all of the usual fire blight models predict continued risk to blooming trees today and into this week. As there are fewer blossoms out there in many orchards (although inland/upland orchards may be in full bloom still), it may be easy to think that we’re out of the woods. However, I would consider treating high value blocks of young trees of fire blight-susceptible varieties, at a minimum (cider varieties, Gala, Mutsu, Cortland, Paulared, Northern Spy, Fuji, Macoun, etc). Word on the street has it that the streptomycin supply is low to unavailable. I’d suggest treating what you can with what you have, consider Apogee / Kudos even at half-rate to reduce shoot blight, and paying close attention to strikes as they show (and cutting them out aggressively).

Many folks are seeing the beginnings of petal fall and are considering an insecticide or thinning treatment containing carbaryl. Please reconsider that if you have any bloom, including in groundcover, in the orchard. I can’t in good conscience (nor legally, in keeping with the insecticide labels) recommend both treating blossoms with streptomycin while also applying an insecticide in a thinning program. So if you have blossoms but want to thin, I’d recommend NAA (Refine) or 6-BA (Maxcel) alone without carbaryl. This looks like a decent week for thinning.

Spray conditions look best tonight (Monday May 23) though Wednesday.

Orchards around the state are either in bloom (inland) or at/approaching petal fall (Champlain / Connecticut Valleys). This is always a tricky time for management, and growers may need to be ready to apply different treatments to different parts of the farm. Here’s my quick rundown:

Insects: Generally, there are still too many flowers out there- both apple blossoms and dandelions on the orchard floor to be spraying without impacting pollinators. In few cases is a pink insecticide spray needed, in my opinion, especially in retail-oriented orchards. Keep an eye on traps, and if you haven’t hung any yet, at least get your codling moth traps up to determine your biofix date. Point being: be ready to treat after bloom (and mow those groundcover flowers first), but don’t get knee-jerk. Wait and see, for now.

Diseases: Fire blight risk decreased this week with the onset of cooler weather, but is shooting right back up with this weekend’s expected heat. There are a lot of flowers still out there, even on petal fall-adjacent cultivars. Apple scab is primed with very high ascospore maturity. Any decent wetting event is likely to cause an infection, so keep covered with a protectant fungicide and use a single-site SDHI, Strobilurin, DMI, or combination material if you have any questions about coverage going into a wetting period.

Thinning: It’s looking like a heavy bloom year, so aggressive thinning is probably going to be called for. Plan on, at a minimum, a petal fall application, followed up by another at 7-14 mm fruit size. Successful thinning depends on many factors, I’ll highlight them more in light of upcoming weather in a few days. Be sure to adjust materials based on the NEWA Apple Carbohydrate Deficit Model. I’m also including Dr. Duane Greene’s advice from a recent UMASS Healthy Fruit Newsletter here.

“Bloom and Petal Fall Thinning

Duane Greene

Flower development has been erratic and proceeding in fits and spurts. However, it does appear that development in many orchards is approaching or will be at full bloom this week. The bloom and petal fall stages are excellent times to start your chemical thinning.

Bloom and Petal Fall

Bloom is a time when orchardists frequently do not choose to thin. The bloom period has not yet occurred so there is uncertainty about how favorable it will be for bees to fly. Also, the potential for frost still exists. However, it should be noted that the sooner you can start the thinning process, the better chance you have of influencing and encouraging return bloom. There are several options available to use at bloom.

Petal fall is a thinner time of application that most orchardists choose. The pollination period is known and there is a reduced chance of frost. If a bloom thinning spray was not applied a petal fall application of a thinner becomes very important.

With one exception (Carbaryl) the same hormone thinners can be used at either bloom or petal fall. When selecting a thinner(s) it should be emphasized that thinners are not as potent when used at bloom as when they are applied at the traditional 7-14 mm stage. A rough rule-of-thumb is that thinners applied at bloom and petal fall are about 50% less effective at thinning as they are if they were applied at the 7-14 mm stage.

Naphthaleneacetic Acid (NAA)

NAA has been used by growers for over 75 years. There is some comfort in using a compound that has passed the test of time. I routinely suggest application of NAA at 10 to 12 ppm. I have never over-thinned a tree using these rates. Lower rates will be less effective. NAA at 10 to 12 ppm could be applied to a broad spectrum of cultivars.

Naphthaleneacetamide (Amid-Thin)

This is a thinner that has garnered increased interest from growers recently. Amid-Thin is a weaker thinner than NAA and it rarely, if ever, over-thins. It has a reputation for being a reasonably consistent thinner. The label allows application of up to 8 oz/100 gal. I do not recommend using a rate any lower than 8 oz/100 gal. (Ed. note: Amid-Thin W is not currently registered in Rhode Island.)

Ethephon

Ethephon may be used as an early thinner. The recommended rate is 300 ppm or 1 pt/100 gal. Some have applied it at a rate as high as 400 ppm with good results. It may not be as consistent as other thinners but it remains a viable option. Since it produces ethylene it may also be useful to enhance return bloom.

Carbaryl

Historically, this has been the most popular thinner in New England. Unfortunately, it is very toxic to bees so it can not be used until the bees are removed from the orchard at petal fall.* Carbaryl is unusual as a thinner in that its effectiveness is concentration independent. It is routinely used at 1 pt to 1 qt/100 gal. Carbaryl is an excellent choice to combine with either NAA or Amid-Thin at petal fall to enhance thinning activity. I like the addition of carbarly with Amid-Thin to enhance the thinning activity of Amid-Thin.

Petal fall is a somewhat nebulous term. I consider it to be a period of time between the time petals fall from the flowers and when the receptacle starts to grow. Early in this period the receptacle is not growing, or growing very slowly, so there is little carbohydrate demand exerted by the fruit. Consequently, I generally do not pay much attention to the carbohydrate model during this period of time. However, when fruit grow to 5-6 mm then the carbohydrate model plays an important role in making thinning decisions.

Bloom and petal fall thinner applications are an important component in a comprehensive thinning program. This opportunity to help regulate crop load should not be missed. The real danger in bloom and petal fall thinning is not over-thinning but not thinning enough!”

Here’s what I’m putting on the orchard this morning: mancozeb @ 4 lb/acre (last application before switching to captan); Inspire Super (difenconazole / DMI) @ 12 oz/acre; Harbour (streptomycin) @ 1 lb/acre; Refine 3.5 WSG (NAA, thinner) @ 6 oz/acre / 15 ppm @ 100 gallons water/acre).

With the heat last week things moved fast, vines at the UVM vineyard range from bud burst to 1-2 inches of growth. 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 may wish to 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 is 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 be relatively brief, since everyone needs to do the same thing. With orchards at tight cluster to early pink bud stage (I appreciate everyone who is reporting their stages at this link), more significant heat, and a rain event expected late this weekend, we are looking at a double whammy of apple scab and fire blight infection events. Here’s me take, and it has a lot to do with your conditions and how quickly you can cover your orchards.

I don’t like spraying, especially fungicides, especially captan or sulfur fungicides, in the heat. If you can get a good coverage on in the next couple of days in the cooler parts of day, that would be helpful. Tissue is expanding rapidly now, so contact material that redistribute with rain would be useful tools to keep some coverage on. That would be captan or maybe sulfur (if organic), which may be a little too close to an oil (within 7-10 days) application to use. Next preference would be mancozeb, which tends to stick to plant tissues a little better. I would consider adding one of the more advanced single-site products in this spray to help with rust and powdery mildew as well- consider a strobilurin, SDHI, or DMI material, tank mixed with that contact material I just referenced. None of those are available to use in organic systems, so sulfur it is.

The plant growth regulator prohexadione-calcium (Apogee, Kudos) helps to reduce tree vigor at full rate, but even at ½ rate applied pre-bloom can help to thicken plant cell walls, which reduces susceptibility of growing shoots to fire blight. It would not be a bad idea to include this in the fungicide spray.

Fire blight protection needs to be applied to open blossoms 24 hours before or after a wetting event. Assume that you are in a full red alert infection potential after Friday, so any open blossom should be treated within a day of wetting. That means being ready likely Saturday or Sunday to apply first streptomycin (only choice I recommend if not organic) spray, if organic, I would consider alternating a ‘sanitizer’ like low-rate copper (Cueva, Badge, etc.) if growing for cider or russeted fruit are not a concern, oxidate, or low-rate (0.5%) lime sulfur followed up within a day with a biological like Blossom Protect, Serenade, or Double Nickel. Strep sprays should contain Regulaid or another wetting agent- that may exacerbate heat-related phytotoxicity from captan.

All of this is dependent on when your blossoms open vs when the rain comes. Some growers may want to put everything- fungicide(s), bactericide, wetting agent, PGR, into one tank. That’s doable but can be risky, especially in regards to phytotoxicity. Then again, that may be the best tactic at this point. Notice I did not mention insecticides nor foliar nutrients in these sprays. I don’t recommend either. For most retail-oriented growers, a little tarnished plant bug won’t affect you fruit value. For the few wholesale growers, you know if TPB has been a problem and have already been ready with a pink spray regardless of what I say. Given the state of pollinators and that the blossoms are right around the corner, I’d steer clear of insecticides unless you know you need one, and even then, do notapply if anything so much as a dandelion is blooming.

Start thinking about your thinning needs soon, but it’s too late for me to make any suggestion there, yet.

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.

This is a big week ahead. Many orchards are at tight cluster bud stage, and with the warm and eventually hot weather coming up, bud stages are going to move fast. Anything you want to do prebloom should be done this week. That means foliar nutrient– zinc, boron, and nitrogen should be applied to improve bud and blossom viability. Oil may be applied for mite management, too, up to 1% up until tight cluster-early pink. But I would not mix oil with nutrients nor captan/sulfur. Nutrients are more important now.

With bloom and hot weather approaching, the biggest disease consideration – no scab is expected for the week with the dry weather, but apply a fungicide before expected wetting periods- is fire blight. This has the potential to be a big infection period.

Let’s look at the conditions required for infection:

1. Open blossoms.

2. Wetting. This doesn’t have to be a rain, a heavy dew or spray application could be enough to cause infection.

3. Heat during and after the wetting event. Later this week ‘they’ are predicting temperatures in the 80s with chance of thundershowers.

4. Build-up of sufficient population of the pathogen to trigger infection. This is known as the Epiphytic Infection Potential (EIP) and requires a) an overwintering or introduced pathogen source and b) heat prior to the infection that allows for that bacteria to multiply. NEWA models suggest that EIP sufficient for infection could be reaches statewide by Thursday.

Follow the NEWA model daily to best assess fire blight risk for your site.

I recommend that all growers with high-risk blocks (young trees of susceptible varieties, sites with a history of FB infection in the past couple of years) be ready to apply streptomycin to all blooming blocks.. Remember, a treated blossom is a treated blossom, so if an infection event extends more than 48 hours (you have 24 hours protection before and after the application time), you only need to re-treat if more blooms have opened.

For organic growers, streptomycin is no longer allowed by NOP standards. Some materials that may be effective include lime sulfur, which burns flower tissues so will only help a blossom that is already pollinated; low-rate copper materials like Cueva and Badge, which may russet fruit; and biologicals like Double Nickel or Serenade. None of those are as effective as streptomycin but each may be better than not treating at all in an infection situation.

I do want to mention another material that may provide some other protection. Apogee is a plant growth regulator that is applied around 1-3” shoot growth (i.e., now) that helps to shorten internodes and reduce the need for summer pruning. It also causes a thickening of cell walls that contributes to reduced shoot blight infection. For young, trellised trees where you may not want to stunt vegetative growth, some reduction in shoot blight has been found using ½ rates. The rate calculation for Apogee is fairly complicated and based on relative need for vigor control and tree row volume. Please see the label for more information.

Your best bet is to be ready to get a strep treatment on this week if you have any concern about this disease. For a good reader on fire blight, see: https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/a4fruitnotesspring2015fireblight.pdf

This is the week to get your codling moth traps up. Traps should be hung at pink and checked daily until first catch is seen. That capture date will be the biofix you use when calculating degree days for subsequent management actions.

Finally, if you have irrigation, this is the week to make sure it’s running.

Stay cool.

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.

First, our colleague UMASS plant pathologist Dr. Elsa Petit is hosting a Zoom meeting for grape growers next Thursday, May 12, 2022, at 12pm. Click here to register. This 30-minute meeting should serve as a great introduction to Elsa and as an informal kickoff to the 2022 season.

At the UVM Catamount Educational Farms vineyard, buds were well-swollen on most varieties this week. Warm, and downright hot later next week, weather should trigger bud break in the days to come. I discovered while assessing the vineyard phenology that one small section of the vineyard had evaded my students’ shears, so we quickly wrapped up pruning that handful of vines, which is always challenging when the buds are so swollen and prone to breaking off.

1Marechal Foch ready to start the season. May 5, 2022.

Despite the dry weather ahead, it will get wet sometime and growers should be ready to manage diseases in the vineyard. We typically recommend fungicides starting around 5” shoot growth, but growers that have had more intense disease pressure may want to start earlier. That could come pretty soon if the warm weather pattern we’re heading into holds. There’s also supply chain issues that may delay availability of some materials. So whether you need mancozeb and captan or copper and sulfur, plan on ordering materials you expect you’ll need ASAP.

Continuing the tradition of the Cornell Grape IPM program, Dr. Katie Gold has again published a recap of season-long disease management considerations that should be required reading for all growers. It is heavy on conventional / non-organic recommendations, but there are recommendations and research results presented from her lab’s assessment of organically-approved biopesticides. Growers should also 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.

My graduate student, Bethany Pelletier, and I will be conducting a trial this season evaluating biopesticides and traditional organic materials (e.g., copper, sulfur) for disease management in cold-climate grape cultivars. Stay tuned for information from that work as the season progresses.

Finally, if you haven’t signed up for VitiNord, the premier cold-climate grape and wine conference which will be held this December in Burlington, please consider doing so. This is a big deal for the state’s and region’s wine industry, and the knowledge and networking shared will be huge.

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.

Orchards are at or around the tight cluster bud stage in Vermont, which means that there is plenty of tissue out there for apple scab to infect, and the disease is in a critical management phase. Orchards should be covered with an effective contact fungicide (mancozeb, captan, sulfur if organic) going into any expected wetting periods. If coverage is questionable going into a wetting event, a postinfection material may be used- Vangard is effective prebloom and during relatively cool weather. There are several others, too- see the New England Tree Fruit Management Guide apple spray table for details. Note that these post-infection materials, including DMIs, SDHIs, Strobilurins, and Anilinopyrimidines, have higfh potential for the fungus developing resistance to them, so always mix with a protectant and rotate fungicide classes every application. Organic growers have fewer options for postinfection materials. I am not recommending liquid lime sulfur anymore, as it is just too caustic and dangerous to applicators, trees, and equipment. Some materials such as the peroxide (e.g., Oxidate) and bicarbonate (e.g. Armicarb) based fungicides have shown efficacy when applied during infection, as the spores are germinating on wet leaves, but are pretty limited in providing any real control after cuticle penetration has occurred. Bottom line: keep the orchard covered.

There is still time to apply oil to manage mites and scale. I am a proponent for putting oil on as late as possible, up to tight cluster or even pink. The rate should be adjusted down as buds open more: 2-3 gallons per 100 gallons water (straight % in tank, not adjusted for tree for volume or per acre) is good from dormant through green tip; 2 % GT-tight cluster; and 1% as you approach pink. Oil should be put on dilute- slow down and open up your nozzles if you can. For most orchards, 100 gallons of water per acre should be the minimum for applying oil. That means recalibrating your sprayer in many cases.

Trees are approaching their peak energy needs as bloom approaches. Now is a good time to get your first soil-applied nitrogen fertilizer down. In many cases, split applications are more useful than a single application, timed at tight cluster to pink and a second application at petal fall. Without a foliar analysis (which is always the gold standard for developing fertilizer recommendations), growers should err on applying a total of 30-40 pounds of actual nitrogen per acre whether in one or two applications. This is also a good time to apply the foliar tonic of urea (3#/100 gallons), boron (1# solubor or 0.1-0.2 lb actual B/100 gal) and zinc (many materials, use label rates). I wouldn’t mix this tonic with oil, do one and then the other in this next spray or two if needed.