VT Apple IPM – More codling moth materials

A good question came up today regarding my recent recommendation on codling moth management: “Saw your note on Codling Moth and was wondering if Assail or Leverage or Belay would work as well as what you listed (Intrepid, Altacor, Belt, Rimon)?”

It’s helpful to have someone read your words back to you. The materials I mentioned are all pretty targeted, if not specific to, lepidopteran pests, and are all effective against codling moth. My unspoken statement was that if you are only targeting CM and want to use a ‘softer’ material, these fit the bill. But certainly, if you still have fresh curculio activity, or just have another material ready to go in the shed, a more broad-spectrum pesticide is fine to use. Assail, Delegate, Imidan, Voliam Flexi, and Danitol are other materials rated at high efficacy against CM in the New England Tree Fruit Management Guide. By all means, use them. Managing CM in high-pressure orchards is pretty critical now.

Take care. I’ll be out tomorrow morning with a tank of Intrepid and Calcium at the crack of dawn tomorrow morning. Were I in the commercial business, I might consider one last fungicide before calling it good for apple scab, but it’s important to get the fire blight I’ve seen out of the orchard and the 4-hour REI on Intrepid is pretty key to getting that done.

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.

VT Grape IPM – Peak disease management

I apologize for this overdue communication. Some grapes at the UVM Vineyard in South Burlington were starting bloom yesterday, and we are in peak disease management season. I’ll keep this brief:

  1. Pretty much every major disease is likely active now, including black rot, Phomopsis, powdery and downy mildew, and anthracnose. Vines should be protected with the best materials in your toolbox. For non-organic growers, that means mancozeb or captan plus a DMI (FRAC code 3, e.g., Rally, Vintage, Inspire super) or strobilurin (FRAC code 11, e.g., Flint, Sovran, etc) material. Rotate those FRAC codes and do not use materials with the same code more than twice in a row.
  2. For organic growers, this is the window to be using whatever copper material you choose.
  3. Keep fungicide coverage on at 7-14 day intervals, shorter as there is more rain.
  4. Keep an eye out for grape tumid gallmaker to be popping up. If these have been a problem in your vineyard, Movento or Assail are your best materials. I don’t know any organic option, so you’ll need to remove them by hand.
  5. Shoot thinning is still critical now, the sooner it’s done, the more resources you will leave for the remaining shoots. Shoots have not lignified enough to do any combing.
  6. If you suspect any nutrient deficiencies, this is a good time to collect petiole samples for analysis. I prefer the veraison timing, but bloom sampling allows for correction this season if somethings comes up particularly low. Details on petiole sampling can be found here.

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.

VT Apple IPM – ‘Cover’ spray time

Category [tree fruit; IPM]

June 8, 2021

Sorry- I’m late on getting anything out, so I’ll cover the high points that are important for managing Vermont orchards in the next few days / week:

  1. It’s time to get a codling moth spray on for many orchards. CM is best managed by using the NEWA degree-day model. For your site, enter the first pheromone trap capture (Biofix) or, with less certainty, let the model predict emergence (that’s the default). Most materials should be applied between 100 and 200 degree days (base 50°F) from that date. For most orchards, that is now. A lepidopteran-specific material like Intrepid, Altacor, Belt, or Rimon (latter two should have been on a few days ago) is best against this pest.
  2. Plum curculio still has some activity left in it for this season in most orchards. If you covered the orchard with a relatively broad-spectrum insecticide at petal fall, border sprays will suffice to keep late-season damage down.
  3. Apple scab primary season is done pretty much everywhere. Scout the orchard meticulously for signs of scab, if you have it, keep up a Captan program until things are burned out. Otherwise, fungal diseases are probably good for a little bit.
  4. Fire blight- Streptomycin works!! We have tow partial rows at the UVM orchard with many dead trees that I plan to rip out (that’s another story), so I haven’t bothered spraying them this year. They are right in our Fire Blight-riddled cider block, which is 95-98% clean right now, but those Spitzenburgs are toast. Scout your orchard carefully for signs of the disease and plan to prune out ASAP, on a dry day. Except in the case of hail, do not apply streptomycin to an orchard that shows symptoms of the disease.
  5. Fertility- If you’re applying nitrogen, start making plans to back off and shut it down soon. This is a great time to apply magnesium, potassium, and other cations if our soil or foliar analyses calls for them.
  6. Every spray this time of year should include some calcium. On Honeycrisp, calcium should go on even if another spray material isn’t needed.
  7. Keep an eye on thinning. This has been one of the most inconsistent years I have seen in my time with this crop (25 years) and I’m seeing and hearing of fruit densities all over the place. It’s getting late to apply thinners, so while scouting for Fire Blight, keep an eye out for trees that need a little hand thinning.
  8. Water, if you can. Many areas of the sate are running dry, and we’re still in the window of maximum cell division that determines fruit size and quality.

All for now,

Terry

VT Grape IPM: Things are taking off

Vine growth is really ramping up in Vermont vineyards, which means that the next two months are critical to set the stage for a quality vintage for 2021. I often say that, once established, grapes are weeds, and I’ll stick to that assertion. However, there’s a difference between a plant that can grow profusely and managing it to provide optimal crop quality. It’s our jobs as farmers to manage the vines for our needs- that what makes us different from foragers of the wild grapes that indeed do grow like weeds all around us.

Top of mind right now should be two practices: shoot thinning and disease management. Shoot thinning is critical to channel the vine’s energy into an appropriate number of shoots to maintain vine balance, and to high quality shoots to ensure consistency of ripening. We typically target 4-6 shoots per foot of canopy. So, vines on six-foot spacing should have about 24-36 well-spaced shoots on them, assuming they have filled their space. Adjust that as needed- vigorous vines get more shoots, less vigorous ones fewer. Now, since they haven’t lignified, you can just pop them off with your fingers. Be sure to select the most consistent and healthy shoots to leave behind. On many cultivars, the secondary shoots, which will be behind in development and thus smaller than the primary shoots, may emerge from the same bud at the base of a more desirable shoot- break those off. Remember thought that breaking off shoots is likely to remove the basal buds that could form next year’s shoots, so you only want to break these off that are in a position where you do not want a renewal spur for next year. This is a great time to strip shoots off the trunk from the fruiting zone down to the trunk base, but leave a sucker or two at the bottom as a renewal option in case the trunk freezes out or is otherwise damaged. I explain this process in a video here (15 minutes, pardon the wind noise); my colleague at Cornell, Dr. Justine Vanden Heuvel, describes in more succinctly using Vinifera cultivars in slightly different training system here.

This is a typical time to start thinking about a spray program to manage disease. 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.

As a reminder, a refreshed version of the Initial IPM Strategy for New Cold Climate Winegrape Growers is available at: https://www.uvm.edu/~orchard/fruit/pubs/Factsheets/UVMFRT004_initialIPMStrategy.pdf

Organic growers are in for a bit more work. The standard fungicides, copper and sulfur, have only fair efficacy against this disease at best, and in a couple of weeks when black rot becomes the next disease of concern, those materials will have even less efficacy against that disease. The first line of defense in an organic vineyard is a strict sanitation program. This includes removing all mummies still in the canopy (not dropping on the ground, but actually removing them from the vineyard) as well as any obviously diseased wood. Phomopsis and anthracnose both overwinter largely on infected wood in the canopy, and removing this wood during dormant pruning or now is essential to reducing disease pressure. Stubs left at the ends of spurs should now be removed since you can see where this year’s shoot growth will resume (at the developing shoot)- these stubs will die and may become infected with phomopsis this season (or were last season) .

Removing stubs at end of retained spurs.

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.

Despite the rain we just received, most sites in Vermont are still running very dry. Established vines on most soils should be okay, but consider watering young vines. I’ll discuss soil fertility later this week.

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.

Honeycrisp Virtual Meetups

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Virtual Honeycrisp Meetup – A three-part series of conversations about Honeycrisp

Researchers, extension specialists and grower panelists;
New York grower Rod Farrow; Michigan grower Chris Kropf and Washington grower Bruce Allen

Join us and bring your experience and questions!
Register to each date in the links below.

JUNE 3rd
CROP LOAD MANAGEMENT
Register

JUNE 17TH
ROOTSTOCKS
Register

JULY 1ST
NUTRIENT MANAGEMENT
Register

Facilitated by B. Sallato WSU Extension, M. Miranda Sazo Cornell Cooperative Extension, and A. Wallis MSU Extension. Supported by IFTA, USDA-SCRI Root2Fruit project and Good Fruit Grower.
For more information visit http://treefruit.wsu.edu/event/virtual-honeycrisp-meetup/2021-06-03/

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VT Apple IPM: Petal fall thinning meeting TODAY, 1PM

I want to get this one out quick:

(Cornell) Champlain Valley Virtual 10-12mm Thinning Meeting Today at 1PM
The Champlain Valley 10-12mm meeting will be held today from 1-2PM. At this meeting, Dr. Terence Robinson will discuss his thinning recommendations for the 10-12mm timing. To join, simply click on the link at 1PM.

Join Zoom Meeting

https://cornell.zoom.us/j/99544274591?pwd=NHZkZU1HK2ZmTDkvc2hCeHhCdW96QT09

Meeting ID: 995 4427 4591

Passcode: 288556

One tap mobile

+16468769923,,99544274591# US (New York)

+16465189805,,99544274591# US (New York)

On that note, here’s my quick rundown of things to in the orchard:

  1. Manage plum curculio. This should be pest # 1 right now, and with hot, humid weather, its activity should be pretty high. PC is active from petal fall but especially at 8-12 mm fruit size, until 308 degree days (base 50°F) after petal fall. There is a model in NEWA, use it.
  2. Codling moth is pest #2. If you monitored CM in pheromone traps and recorded first date of capture, use that in the NEWA model, or hand calculate degree days (also base 50°F). Sprays should be timed at 150 DD for ovicidal materials (Rimon, Intrepid, Esteem) or 250-360 DD for most other materials. As usual, use the New England Tree Fruit Management Guide to help guide selection.
  3. Start adding calcium to sprays any time now, especially on Honeycrisp.
  4. While we’re talking nutrients, trees are in their main flush of growth, so any nitrogen fertilizers you’ll be applying should be going on now.
  5. Water! Things are really, really dry out there, and that’s not looking to change any time soon.
  6. Because of that, apple scab is on the back burner, mostly. When we get rain, scab will be an issue. When you next spray, make sure you’re staying covered.
  7. There are a lot of reports about powdery mildew showing in area, which does not require leaf wetness, only high humidity. For orchards with a history of PM and with susceptible cultivars (Cortland, Gala, Ginger Gold, Idared, Jonathan, Mutsu (Crispin), and Paulared), you may want to include a material with some efficacy against the disease. From the NETFMG: “The most common multi-site fungicides, captan and mancozeb, are ineffective against powdery mildew. DMI fungicides vary in effectiveness. Unfortunately, the DMIs most effective against powdery mildew, Rhyme, Rally, Rubigan and Procure, are least effective against scab, and vice-versa. QoI fungicides, Flint, Flint Extra and Sovran (and pre-mixes with Group 11 ingredients) have good efficacy against powdery mildew. SDHI fungicides, Aprovia, Fontelis and Sercadis (and pre-mixes with Group 7 ingredients) are somewhat less effective, but still provide good control. Low rates of sulfur are effective in low disease pressure environments, such as New England, but the risk of sulfur injury increases as temperatures go over 85°F. In organic production systems, sulfur applied at weekly intervals, and bicarbonate and peroxide-based fungicides applied on 3-5 days intervals are the best options. (TB note: in my 12+ years of growing apples organically using sulfur to manage scab, I never saw PM in orchards managed using that system.)
  8. Keep an eye out for fire blight infections. If you find any, cut them out as soon as you do. But, please send me an email, as my colleague Dr. Kerik Cox at Cornell is tracking Erwinia amlovera (the causal bacteria of the disease) strains in the northeast and testing for streptomycin resistance.

Okay, that’s all for now. Who knows a good rain dance??

VT Apple IPM: Petal fall thinning meeting, fire blight clarification

From our colleagues across the lake at Cornell University. This should be a very informative meeting. -TB

The virtual Champlain Valley Petal Fall Thinning Meeting will be held on Tuesday, May 18, from 4-5pm. At this meeting we will hear from Dr. Robinson on his thoughts for thinning at the petal fall timing. To join, simply click on the zoom link on Tuesday at 4pm.

Join Zoom Meeting

https://cornell.zoom.us/j/99544274591?pwd=NHZkZU1HK2ZmTDkvc2hCeHhCdW96QT09

Meeting ID: 995 4427 4591

Passcode: 288556

One tap mobile

+16468769923,,99544274591# US (New York)

+16465189805,,99544274591# US (New York)

Clarification on Fire Blight notice:

A couple of people have asked if it is safe to apply streptomycin when bees are in the orchard. To my knowledge, there are no indications that strep is harmful to bees. In fact, its labeling to be applied during bloom indicates that it has passed the EPA standards for pollinator safety. The outlook for fire blight has only gotten more favorable for this week, given the warm weather expected at the end of the week. If you have open blossoms Tues-Fri, I’d plan to treat sometime during that window.

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.

VT Apple IPM: Yup, fire blight risk is on the rise this week

As I mentioned yesterday, fire blight risk is on the rise in all orchards in Vermont.

Too long / didn’t read synopsis: if you have open blooms (and you likely do), check NEWA and be ready with a streptomycin application this week.

With increasing warmth, the population of bacteria that causes fire blight is rapidly multiplying. Let’s look at the conditions required for infection:

1. Open blossoms.

2. Wetting. Everywhere in the state has a chance for some wetting this week, including heavy dew or even a spray application

3. Heat during and after the wetting event. This is marginal, but if there’s a high enough bacterial load, then infection could occur.

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.

In the few hours since I first checked the models this morning, they have already increased risk for this week, at least at my South Burlington 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) apply streptomycin to all blooming blocks (don’t forget those lagging ‘rat tail’ blooms) tomorrow (Monday 5/17) or Tuesday. 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 many orchards at full bloom, that may mean that you’re just treating once, but for cooler sites where bloom is just getting going, that may mean to applications.

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 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

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.

VT Apple IPM: NEWA Apple Scab Model

I’ve heard some confusion about apple scab this week, and chatter that the apple scab model in NEWA isn’t working correctly. Please let me reiterate what I said a few weeks ago. Models are just tools that helps understand what’s going on in the orchard, based on data (from weather stations, generally) and assumptions (about biology). NEWA is great, because it outputs a clear, green/red indicator of a disease infection event. But neither the data going into those models nor the biology in the orchard are that cut and dry.

TLDR: Keep your orchard covered with fungicide this week. Period.

The small, intermittent rains and wetting periods can add up to a large spore release and infection if you’re not covered. Because of the intermittent nature of this week’s rains, NEWA models appear to be correcting (maybe changing is a better word) almost daily, and orchards within short distances of one another show different results. None of these events so far this week has added up to one major infection event, but cumulatively, you could have a decent infection on your hands, and if you’re waiting for NEWA to scream red, you could be too late. Also, you run the risk of facing poor spraying conditions or just not having buildup from prior applications should a decent wetting event come. It’s one thing if you can spray your orchard in an hour, another if it takes a day. Keep the coverage on.

The NEWA scab models require a number of assumptions. First, ascospores, which are released from overwintering inoculum from last tear’s infections, mature according to a fairly reliable growing degree day accumulation. If that incoming data gets off (as happened on some stations in the region, since fixed), or a sufficient dry period occurs, the model may not accumulate development in-line with what’s happening in the field. Once we have mature spores, they need a wetting event, typically considered between 0.01-0.1” of rain, to be released from the leaf litter. More release in the daylight than at night, but a small percent of ‘night spores’ from a large inoculum can be significant. Then we need the leaves to be wet for a certain number of hours depending on the temperature. And those wetting hours can be cumulative across a number of days if the dry periods in between are less than 24 hours. This makes for a pretty complicated model.

This also makes for some potentially bad decisions if we’re waiting for this model to give us an overly simplistic change from green to red, when in reality, there are gradations within that model determination, and fuzzy distinctions and limits among all of those assumptions mentioned.

That said, the NEWA scab model is indeed running as it should. The earlier quirks have been dealt with, and I expect that any delayed ascospore maturation from dry spells has caught up to the statistical confidence interval built into the model.

We’re in the peak of primary ascospore season, everywhere in the state. There are chances of showers most days this week. While I applaud good IPM, this is not the time to cut corners. If you have a chance to stay covered with even a basic rate of captan / manzozeb (or sulfur if organic), then do so. Once a week is good, but don’t get caught off-guard. Warmer weather this weekend and early next week also brings potential fire blight infection. Keep an eye on that model daily if you have anything still in bloom.

VT Apple IPM: Pink, Bloom, Petal Fall edition

Here we are on May 11, with bud stages all over the place. I’m seeing trees near me in upland/inland central Vermont at tight cluster bud stage; hearing reports from Bennington of trees at pink; and have trees at our orchard in full bloom and starting to lose a few petals. 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 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. However, the drawn-out prebloom period may increase the time that sensitive tissue is out there to be fed on by numerous pests. 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 is really low, as temperatures have been too cool anywhere for bacterial populations to build up. Keep an eye on NEWA if you have later blooming cultivars and the weather starts to warm up. Apple scab, on the other hand, 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. This week is a bit tricky to time the sprays, as there has been and continues to be a low top moderate chance of rain most days this week, but not really enough to know for sure if a spray would be wasted.

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!”

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.

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