VT Apple IPM: Thinning, fire blight, scab

May 20, 2021

It’s looking pretty hot out there in more ways than one. Many orchards are at or near petal fall, but those with bloom should be keeping the streptomycin sprays on, with all this heat we’re having. Fire blight remains a concern statewide, and I would expect some infection in any orchard that has sufficient inoculum. That last part is important, and yet hard to quantify. Certainly if you’ve has the disease in the past, especially in the last two years, it’s likely that it will show up. The next disease concern is apple scab. Any promised rains keep getting pushed back in the forecast, now Saturday-Sunday looks like the most likely chance for any substantial rainfall. Whenever it comes, we should be prepared with a good coating of protective fungicide. Most growers are switching over to captan now which is fine, but be careful not to mix with Regulaid if you’re using that wetting agent to improve strep penetration into blossoms, as the combination of that, captan, and heat will likely cause leaf burn. If you’re looking at a second application of strep after one that already had a wetting agent included, you can leave it out this time. It’s also nota bad idea to put something in that would provide broader disease control, like an SDHI, SI, or DMI fungicide (take your pick from materials with FRAC codes 3, 7, 11 here, and always rotate FRAC codes after two successive applications of the same one).

Growers at 100% petal fall may want to consider adding in an insecticide against European apple sawfly, plum curculio, and early codling moth. However, if you have any blooms remaining, including in the groundcover vegetation, I recommend holding off on applying any materials harmful to bees and other pollinators. I typically include some Dipel or other Bt product in this ‘almost petal fall’ spray to help keep lepidopteran pests like green fruit worm and obliquebanded leafroller at bay while I wait until the following week to apply something more broad spectrum like Avaunt, Actara, or even Imidan if you’re still using organophosphates. Sevin applied in a thinning spray will have some efficacy as an insecticide, but not a lot.

As for thinning, it’s time to get on it. Blooms are heavy this year, and the sooner you remove resource competition and gibberellin formation from excess developing seeds, the more likely you will get reasonable return bloom next year. If you still have any bloom, or just want to stay away from it, please leave the Sevin / carbaryl on the shelf. With the hot weather, trees are going to respond well to thinner applications anyway, so an NAA or 6 BA spray should suffice. Pick one- the former is typically good on McIntosh and most large-fruited cultivars, the latter on varieties that tend to produce smaller fruit (Empire, Gala, Fuji, Macoun). See specific recommendations here.

For cider apple growers, I don’t have a great recommendation for managing biennialism on European cultivars. The need to thin for fruit size is less of a concern than for dessert cultivars, but you don’t want to overstress the tree and have no crop this year. I would plan on multiple applications of NAA, say bloom, petal fall, and at 8-10 mm fruit size, to encourage return bloom.

For what it’s worth, here’s the tank mix I plan to apply tonight or tomorrow morning: Captan (5 lbs/ac), Merivon (5oz), Dipel DF (1 lb), Refine (8 oz), Harbour (24 oz). This is to a very mixed orchard of ~50 varieties in all stages of bloom to petal fall.

VT Apple IPM: Buds are moving fast

At the UVM Horticulture Research and Education Center orchards in South Burlington, buds rapidly moved toward and past the half inch green bud stage yesterday, depending on cultivar. Two more days in the 70s will just keep things moving. This is heading toward one of the earliest seasons in my recent memory.

Good news: things look to cool down a bit next week, with no frost in sight. Buds at half inch green can withstand temperatures into the low 20s (°F). There is also a pretty heavy potential bloom this year, so even if a percentage of buds are damaged, we may do all right in the end.

Bad news: as buds open further, they lose hardiness, so by tight cluster, we start to see damage in the mid-upper 20s.

Be careful of snake oils out there that purport to boost hardiness, but do consider getting foliar nutrition on a bit earlier than normal. And speaking of oils, now is a perfect time to get your oil on to manage mites and San Jose scale, the latter of which is becoming an increasing problem in area orchards.

Good news: dry weather means no scab.

Bad news: no scab development doesn’t mean the disease is going away, just that its development is slowed. You’ll need to deal with it sometime. Also, I’m concerned about water for the trees already- if you irrigate, get ready asap. If you don’t, think about installing a system.
Regional note: there is an increasing chance for rain in central and especially southern VT Sunday night into Monday. The further south you are, the more important it is to be covered.

Good news: no insects to really think about yet, aside from pollinators that are just emerging from their ground burrows, especially in sandy soil.

Bad (?) news: get your tarnished plant bug and European apple sawfly traps up asap. Three white sticky cards per block, half knee height (TPB), half head height (EAS). Check against the threshold table and quick scouting guide you have printed off and put on the refrigerator.

Good news: weather is looking great for spray applications.

What to do:

  • Apply copper to any blocks you haven’t yet, but back off as bud stages hit half inch green (HIG). Cuprofix seems to be the main material used now but really, any of the high metallic ion formulations will work. Use full label rates, but back off if you’re interpretation of HIG is being conservative to justify putting copper on that should have gone on this past week.
  • If you’re already past five days or so from your copper spray, and you’re south of, say, route 2, it may not be a bad idea to put on some mancozeb to provide some protection from the potential wetting event. Warmer sites may have 5-10% of apple scab ascospore mature and significant tissue exposed on advancing buds. You could also consider a cool-weather early season fungicide like Syllit, Vangard, or Scala to give a bit more boost if the wetting event is looking greater.
  • This is a perfect week for applying oil. Mix by solution, not rate per acre, and drop your speed down to really soak the trees. 100 gallons per acre minimum should be the plan. Adjust your rates down as the buds open up: 3% (3 gallons spray oil / 100 gallons water) is fine through early green tip; 2% through tight cluster; 1% as you get into open cluster and pink. Copper and mancozeb can be sprayed with oil, sulfur and captan definitely not.
  • When you can, apply foliar nutrients. This is a great time to apply Dr. Warren Stiles’ ‘cold weather prebloom cocktail’ of nitrogen (urea (3 lb./100 gallons dilute, or one of the liquid formulations like N-Pact at label rate), zinc (use label rate of your favorite product) and boron (0.1 -0.3 lb. B/acre). I would do these separate from the oil, maybe later in the week when more leaves have emerged to catch them and we don’t have to worry about the oil causing burning with the nutrients.
  • Separate from spraying, this is great weather to plant trees and do general orchard maintenance. You’re all done pruning, right?

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.

Good week for copper application in Vermont orchards

Most apple cultivars at the UVM Orchard in South Burlington were at the silver tip bud stage when I checked on Friday, with only the slightest but of green tissue showing on the earliest ones (Zestar). I call silver tip when the bud scales at the tip of fruit buds first separate, but green tissue is not yet evident when looking at the bud from the side. Bud stage criteria can be viewed here: http://orchard.uvm.edu/uvmapple/hort/99budstage/BudStageCriteria.html

What does this mean for orchard management? The window between silver tip and green tip is perfect for applying copper to suppress fire blight and to act as your first scab spray of the season. Dave Rosenberger pulled together an excellent summary of the use of early season copper for scab and fire blight management in the March 25, 2013 issue of Scaffolds. But, while early season copper can be an excellent management tool, copper materials can be phytotoxic. That is why the early season spray is made before much green tissue is exposed. If applied when buds are closed, however, then cold temperatures immediately before or after spraying are not a huge concern. In fact, I have in many years had my airblast sprayer fan shroud ice up while applying copper- not an ideal situation, but it can happen at 5 AM when the temperature is 31 F and the velocity of air coming through the shroud contributes to rapid cooling, much like a snow gun on the ski slopes. Oil, however, is a different story when it comes to applications before or after freezing weather. Delayed dormant, silver tip, and green tip are common times to apply an oil spray to help manage mites, aphids, scales, and other overwintering arthropods pests. When oil penetrates cells, it causes phtotoxicity that can affect fruit development, especially when cluster leaves which supply most of the carbohydrates to developing fruit early in the season are damaged. Oil is often applied at dilute rates, and the goal for a grower should be to fully saturate the tree as best possible. Application of oil just after or before freezing events (say 2-4 days) can cause damage, so if you have seen or are expecting freezing temperatures, put the oil away for a couple of days.

Fortunately, oil can be applied right up to tight cluster-early pink bud stages, and in fact may be more effective then. We should be out of frost risk by then (otherwise we have bigger problems than oil on fruit cluster leaves), so maybe delaying your oil application would be prudent, so long as you can fit it around Captan sprays later in the season. Oil should not be applied within 7-10 days of a Captan or Sulfur spray. For more details on spring oil applications to manage mites and other pests, including rates and spray incompatibility issues, please refer to the New England Tree Fruit Management Guide.

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.

Happy Spring, and the 29th March Message

As promised, the apple season has begun today, April 1 with….cold and snow. No, we are not at green tip yet, but I have seen tiny bits of green tissue poking out from some early cultivars and received a report from an orchard in the southern part of the state the other day that they were just around the corner.

I won’t belabor the things that growers need to think about, as a more timely message will be sent once buds start to break. But this is a reminder to start checking your trees regularly and to record bud stages- these are needed for many models in the NEWA system. You also should be tuning up your sprayers, as any day now we’ll be making the call to apply copper to reduce overwintering fire blight and prevent early season apple scab infections.

I would like to take this moment to share the UMASS March Message, which is both linked and attached. This summary coordinated by Dr. Jaime Pinero and the UMASS Fruit Team carries on the tradition of the late Ron Prokopy, who summarized the latest IPM research topics for growers just as the season was beginning.

Finally, anyone who missed the New England Winter Fruit Webinars, which included discussion on sprayer calibration, apple insect pest management, and updates to the NEWA system, can view them here: https://www.youtube.com/playlist?list=PLUL3FZJYGp3n04GfGTlQgoXoKBk7R2Xx7

-Terry

From: Jaime Pinero

We are pleased to bring you the 29th edition of the March Message!

See PDF attached – the table of contents is interactive; clicking on a section takes you to that respective page.

Google docs version:

https://bit.ly/3dhp4yc

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.

29th Annual March Message (2021) .pdf

Important changes to UVM Fruit website, and upcoming winter educational opportunities

As we shift into winter, I’d like to highlight some changes among the UVM Fruit program, and to present a number of opportunities for learning and networking this season. First, our website which has been operating since 2013 was retired on fairly short notice when the background sofytware was retired by . Thanks to the Extension Web Team, we now have a new site shared with the Vegetable Program, now together known as UVM Commercial Horticulture. The site is not completely migrated yet, but is largely in-place at: https://www.uvm.edu/extension/horticulture/commercial. Please update your bookmarks, but save the “…this link is broken…” emails for a bit until we can get things squared away. The complementary UVM Fruit Blog is still available, but will likely be tweaked a bit this winter to make specific material easier to find. Consider the website as the main site for static information, and the blog as a place where I post more time-sensitive material, particularly an archive of all emails sent to our mailing lists.

One of the key outputs of our program is the annual Vermont Tree Fruit Grower Association meeting held every February. Obviously, that is not going to happen this year. On the other hand, we do have a number of online meetings and webinars that will provide opportunity for learning, collaboration, and to acquire pesticide applicator’s recertification credits. These will happen under different banners, so I’ll summarize them below. All of these require preregistration, and each platform has a different sign up.

2020 Vermont Vegetable and Berry Grower Webinar Series registration (all use same link, on right side of page)

  • 12/2/2020: Bags, Liners, Containers – So Many Options – Chris Callahan
  • 12/9/2020: Adding Tree Fruit to a Diversified Farm – Terry Bradshaw
  • 12/16/2020: VVBGA Meet and Greet. Lisa McDougall, Justin Rich, Andy Jones

2020 UVM Fruit Program / VT Tree Fruit Growers Assoc Annual Meeting.

  • 2/18/2021: Meeting hosted by UVM Fruit Program on Zoom; VTFGA will handle registration (watch for details)

2020-2021 New England Winter Fruit Meetings registration page (not all meetings set up for registration yet)

A collaboration among the New England Tree Fruit Extension Professionals. Most of these meetings will qualify for pesticide recertification credits.

  • 1/12/2021: Harvista and SmartFresh on Honeycrisp and Other Varieties; CA Storage Techniques Presenter: Jennifer DeEll, OMAFRA and Randolph Beaudry, MSU
  • 1/19/2021 : Training and Pruning Strategies for Healthy and Productive Peach Trees Presenter: Bill Shane, MSU
  • 1/26/2021: Blueberry Twig Blight Diseases Presenter: Mark Longstroth, MSU
  • 2/9/2021: Cider Apples in 2021: Where Do We Stand? Presenters: Terry Bradshaw and Liz Garofalo
  • 2/16/2021: Invasive Insect Pests: Spotted Wing Drosophila, Brown Marmorated Stink Bug and Spotted Lantern Fly Presenter: Jaime Piñero, UMass
  • 3/3/2021: Managing a Trickster: Adventures in Apple Maggot Control Presenter: Suzanne Blatt, Ag Canada
  • 3/10/2021: Research Update on Early-Season Insect Pests Presenter: Jaime Piñero, UMass and Glen Koeher, UMaine Extension
  • 3/17/2021: Honeycrisp Bitter Pit and Soft Scald Management Presenters: Renae Moran and Glen Koehler, UMaine Extension
  • 3/23/2021: Tree Row Volume: What it is, why it matters and when to use it Presenter: Terry Bradshaw, UVM
  • 3/30/2021: Network for Environment and Weather Applications (NEWA) 2.0 – Project Upgrades 2021 Presenter: Dan Olmstead, NEWA

There are more details to come on all of these, and each will be outlined in later posts. I look forward to a productive winter, and wish everyone the best during this holiday season.

Take care,

Terry

Petal fall

By Terence Bradshaw

I know that some orchards are still in bloom, so the thinning and insect management portions of this message may not pertain. Hopefully everyone with any hint of risk for fire blight has treated sometime during this heat spell. Cooler weather this weekend and rapidly dropping blossoms will decrease risk, but until then, the pump is primed. Everyone also needs to keep an eye out for blossom blight symptoms, and for the shoot blight that will follow. Growers can apply Apogee (4.5-9 ounces per 100 gallons dilute**) any time now to reduce shoot blight incidence. Apogee treatments will reduce shoot elongation and thicken cell walls for about 2-4 weeks post-application, so retreatment may be necessary every 1-4 weeks until terminal bud set.

All set on FB? Okay, we have some big fish to fry this week. Let’s cover them one by one.

  1. This will all be said in light of the heat that we’re experiencing in the next couple of days. If you can avoid spraying anything (streptomycin excepted) when the weather is >85°, that’s a good thing. Then again, don’t ignore the very real threat of the following pests that need to be protected against. I have an inkling that many of us will be up pretty late/ early tonight/tomorrow morning to get things covered while dodging the heat.
  2. We are all headed for a pretty big apple scab infection period starting tomorrow Thursday 5/28 or Friday. Make sure you are covered going into it, I would not count on any material’s kick-back activity to handle this kind of scab load. As I’ve mentioned before, some materials (captan, sulfur) can cause leaf burning when applied ahead of hot weather. But, given what looks like an extended wetting period and an ample load of mature ascospores, I’d take the chance of a little leaf burn over a major scab outbreak. If you want to put on a lower rate now and follow up Sunday or so with a kick-back material (SDHI, strobilurin, or DMI, see here for more discussion, also mixed with a protectant like mancozeb or captan). Everyone should plan on phasing out mancozeb soon, as it it toxic to beneficial predatory mites that do some great biological control or European red mite and two-spotted spider mite, and we’ll soon have to be thinking about its 77-day preharvest interval. Organic growers, I would apply sulfur before and after the rain event, and maybe consider lime sulfur (LS) for the second spray to provide some post-infection control. LS is caustic, nasty stuff, so use it wisely, wear all the appropriate gear, and wash everything down well as it is very corrosive to steel and other materials.
  3. If you’re at total petal fall, then it’s time to start thinking about insect pests, especially plum curculio (PC). PC love this heat and will be ready to oviposit on fruit as they reach 7-10 mm diameter. Organic growers should plan on getting a coating or Surround on trees asap, and maintaining that coverage for about 400 degree days (base 50°F) after petal fall (NEWA has a good model for this). This is a longer window of coverage than for non-organic orchard management (308 dd base 50°F), because Surround does not kill the insects and so must be maintained longer until the biological urge to oviposit has completely subsided. For non-organic orchards, effective materials include Imidan, Actara, Avaunt, Voliam, and Agri-Flex. Carbaryl, if used for thinning (see below), will have some efficacy, but probably shouldn’t be your primary material of choice given the weather that is very conducive to PC activity. Thinning rates of carbaryl are about half the insecticide rate, and I would plan on using just that lower rate as a thinner and use a separate material for my insect management. Any of these materials will help to manage the other petal fall insects, including European apple sawfly and the various lepidopterans (obliquebanded leafroller, Oriental fruit moth, codling moth, etc) that may be emerging at this time.
  4. Thinning. Okay, this is always a tricky one. First, anything applied in the next 40 hours will be highly active because of the heat, so I’d err on lower rates and a lighter touch. A second application may be needed after this weather breaks. Now, I haven’t been in orchards all across the state, but where I have seen bloom from Connecticut valley, Addison county, and our own orchard in South Burlington, it was good to downright heavy. Pollination and fertilization conditions have been just about perfect, so I’d expect trees to need a decent thinning this year. The New England Tree Fruit Management Guide has some good variety-by-variety recommendations, so I recommend starting there. A good, standard petal fall spray of 1 qt/acre of carbaryl and 8 oz/acre Fruitone N or L (I did the TRV adjustment for you) should do the trick for most orchards. For organic orchards, it’s time to start hand thinning. A lime sulfur spray used for scab can help to knock some fruit off, but it’s not labeled specifically for that use.

I think that covers it for now.

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

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Petal fall and spraying this week

By Terence Bradshaw

What an amazing weekend it’s been, weather-wise. I still need to check bud stages, my cider varieties here at 1500’ elevation in central Vermont are still at around half-inch green, and so are not an indicator of what things look like around the state in more typical orchards. However, I imagine many varieties are approaching petal fall, and growers may be itching to put on an insecticide of thinning spray.

The weather for the next three days (Tuesday-Thursday I mean) calls for pretty extreme heat, by May standards, anyway. Given that likely spray materials now include potentially phytotoxic fungicides (captan, sulfur) and insecticides (carbaryl), and that thinners will be very active if applied in this heat, I urge caution. I also don’t like to apply anything in temps of 85° or hotter.

I’ll look over bud stages in the next day or so and check the weather for later this week. Chances look decent for our first apple scab infection period in a while on Friday, and it could be a doozie. Combine that with need to thin and manage post-bloom insects, and we could be in for a complicated spray week.

If you spray anything now, I’d only consider streptomycin on highly susceptible varieties in orchards with recent fire blight infection. In that case, a coat of fungicide (not captan or sulfur because of phytotoxicity issues) may not be a bad idea. But in most cases, I’d lean towards no treatments and plan on an evening / night / crack-of-dawn-when-it’s-cooler treatment window later in the 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, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Fire blight & streptomycin questions

By Terence Bradshaw

I’ve received a few questions about the fire blight alert:

  1. If you are in an inland/upland site and no bloom or fresh pruning wounds, this alert does not apply. However, I bet most apples in the state, aside from some late cider varieties, will be in bloom before this disease alert is done.
  2. Strep can be applied within 24 hours before or after an infection / wetting event. So you could wait to see if there is dew, but need to know that there’s no dew if you decide to hold off. Dr. David Rosenberger from Cornell has also been discussing the possibility that high humidity may be enough to cause infections. Bottom line- I’d get out there sometime if you have any risk (susceptible blooming varieties, past history).
  3. A treated flower is a treated flower. So if you’re at full bloom and you’re going to treat anyway, treat any time.
  4. Rate: I was corrected on the rate of streptomycin that I’d recommended, which I’d passed on from another extension warning without reading the label. Harbour is the main (only?) brand of strep we use in the state, and it is labeled for 24-48 ounces per acre. The first application should include Regulaid or similar wetting agent, subsequent sprays, if applied, can and should omit the wetting agent to reduce phytotoxicity.
    The Harbour label is a bit confusing, as it makes some jumps from concentration to rate with an implied understanding of (and I’d say controversial application of) tree row volume. We’ll discuss TRV another time, not during an important disease event. Stick to the label rate, which is 24-48 ounces per acre.

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, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Fire blight alert

By Terence Bradshaw

I’ll keep this short and to the point. In spite of, or rather in keeping with, what I said the other day, fire blight risk is increasing in Vermont orchards. I’m seeing sustained warm, sunny, relatively windless, and dry conditions for the next 5-7 days, with increasing risk of rain as next week starts. The heat is driving the bacterial population to increase pretty rapidly. Warmth suitable for infection is present. Open blossoms are present. The question is whether ot not you a) have fire blight inoculum in or near your orchard and b) whether or not wou’ll get the necessary wetting to cause infection. For the first one, if you’ve ever had any fire blight in the past couple of years, assume that you have inoculum. The population is moving too rapidly to assume otherwise.

For the second, you may want to wait things out until just before a rain on Monday or Tuesday, but what if ypu miss a dew event? Sunday morning looks like there’s potential for some dew, and that’s enough.

Anyone in any stage of bloom, is to get a streptomycin (or pick your organic biocontrol of choice, but I can’t personally vouch for any at this time) spray on sometime between Friday and Sunday morning. Once a blossom is treated, it’s protected, so later is better to ensure you cover the maximum number of blossoms. But don’t wait so late that you miss a good spray window. Strep should be applied 16 oz per acre in sufficient water to get good wetting, amd I recommend Regulaid or another organosilicone wetting agent be included.

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, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

Bloom, apple IPM

By Terence Bradshaw

Apple bloom has started in much of the state, and the weather looks about as good as it gets for pollination and fertilization. It’s been dry since last Friday, and, in most sites, that rain wasn’t even as much as expected. So, water if you can, trees in bloom and setting fruit have high energy requirements, and water is a key part of mineral nutrient transfer and photosynthesis. While I’m at it, this is a good time to get your fertilizers on. Nitrogen fertilizers should be applied between bloom and June 15, while your potassium and other fertilizers can go down between now and midsummer. It’s also not too late to put on foliar fertilizers, such as the prebloom nutrient cocktail recommended by Cornell University and New England apple experts. However, given the bloom, the dry weather, and minimal disease pressure resulting from that, I’d put the sprayer away for a while- with the caveat I’ll leave below..

It looks like dry weather will be the rule for a while, so apple scab just isn’t an issue. That means that, when we do get some wetting, an pretty good infection period could result, so keep an eye on things and plan to cover ahead of any rains, which look to be at least a week out. When the weather is dry, ascospore maturation goes into hibernation so we can’t assume the spores will all mature and release with the next rain and scab season will be done with in one event. Of course, use NEWA to help keep an eye on your scab and other disease issues.

The disease we really think about during bloom, and especially during a warm/hot bloom, is fire blight. This bacterial disease acts differently from scab and other fungal diseases in two key ways- first, it is essentially internal in the tree, and therefore can act systemically and therefore tends to stick around for a while. Next, its infective pathogen can ramp up its population rapidly under warm conditions. The cool spring so far has kept fire blight danger (measured as epiphytic infection potential, or EIP) down to a minimum. However, that EIP is expected to ramp up fast in the next week:

The fire blight model does assume that you a) have inoculum present, and b) that you have water to move it into blossoms which allow entry into the tree’s vascular system. You can adjust the latter condition a little in NEWA, and the former is a judgement call as far as making an application is concerned. I would have at least one application of streptomycin on-hand and be prepared to treat blooming trees, particularly if you have a wetting event. This could include heavy dew, especially if you have a day afterward that has high relative humidity. High-value, fire blight-prone varieties may warrant a prophylactic treatment going into the weekend, but that’s a tough call.

For organic growers, Actinovate, BlightBan A506, Bloomtime Biological, Blossom Protect, Double Nickel, Regalia, and Serenade are labeled biological controls. I can’t vouch for any of their effectiveness, and I know that some growers apply copper or lime sulfur (warning- both are very phytotoxic) during bloom to manage the disease but again, no promises are offered from me there. If you can, I would suggest Serenade or one of the other biological materials if you have it on-hand and to watch carefully for symptoms which will require cutting out.

Once the EIP is sufficiently high (in NEWA, 100 is considered high enough to cause infection), you need three factors for infection to occur: open wounds (i.e. blossoms or fresh pruning cuts); mean temperature above 60°F; and wetting, even a spray or dew event can be enough to move bacteria into susceptible openings.

This risk is pretty much widespread across the state. The thing to remember is that protective measures, i.e. application of streptomycin in most orchards, or caustic materials/biological controls in organic orchards, must be applied to open wounds or blossoms within 24 hours before or after infection. So if we assume that an infection event occurs in a rain you’ll want strep or another material (really, if your orchard isn’t certified organic, strep is the only material to consider) on within a day. It will be hot Friday, so blossoms will be opening all day (or petals falling on cultivars that have finished bloom already) and potential for phytoxicity will be greater. The later you can go, the better to make sure you cover any blossoms that open, but don’t delay and miss it.

But, make sure to look at the forecast at least twice a day. We not only are not predicting rain, but also, at least for the next few days, predicting dew, either. The NEWA fire blight model output (see above) includes predictions for rain and dew.

Harbour is the strep material available to most growers. I would recommend applying at 1-2 pounds per acre based on tree canopy volume, if in doubt, err on the lower end. I also recommend including a wetting agent like Regulaid or LI-700. If possible, apply on its own, without other fungicides or insecticides (you are in bloom, so no insecticides anyway). You will get leaf yellowing from this application, expect it and the tree will soon grow out of it. One application Wednesday PM-Friday AM should cover you. Once any particular blossom is treated, it’s protected. Temperatures are expected to drop after Friday, which lowers risk, but if high risk continues through the weekend and you keep having blossoms open, then a second application Saturday-Monday (I have no good idea of what the weather will be five+ days from now) may be warranted.

Trees that are at full petal fall are not susceptible, but straggling late blooms can be infection sites. Ideally, the whole orchard would be treated. If you need to prioritize, go first for cultivars that had fire blight in the last two yearr or highly susceptible cultivars (Gala, Ginger Gold, Honeycrisp, Cortland, Paulared, etc), and of course blocks that are in bloom. Application well after any wetting event,will not give protection against it. Also, despite the wording on the Harbour label, continued treatment every 10-14 days after bloom is not recommended (at all- don’t do it), and doing so is a) expensive, b) a waste, and, most importantly, c) the best way to develop antibiotic resistance in E. amylovera populations.

As for insects, there are management actions you can be doing now. Of course, no insecticides during bloom. But you should be checking pheromone-baited codling moth traps at least every other day and noting the date of first capture in order to set your biofix for the NEWA models we’ll use later. Now is a good time to get mating disruption ties for dogwood borer or codling moth up in the orchard.

Finally, keep a good eye on the bloom and on pollinator activity in the orchard. I suspect that this will be a year that we’ll need to really work on crop thinning, even though we’re in an ‘even year’ which, in the past decade or so, has meant smaller total crop overall. We’ll talk about thinning next time.

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