ACCEDE Experimental Use Permit in Massachusetts in 2021 (and what to expect in 2022)

 In late 2020 Valent Biosciences received Federal registration for ACCEDE plant growth regulator. From their announcement “Accede is the first PGR based on a naturally occurring compound developed specifically for thinning of stone fruit, including peaches and nectarines. It also gives apple growers an effective tool to thin apples in the late thinning window when fruit are 15-20 mm in diameter. Until now, no fruit thinner has provided reliable thinning at this stage of development. Use of Accede will reduce the need for costly hand thinning to adjust the crop load and generate higher fruit quality and grower returns.” 

How does Accede work to thin apples and peaches? Accede (active ingredient 1-aminocyclopropane-1-carboxylic acid, ACC) is classified as a naturally occurring “biochemical” plant growth regulator. It is an immediate precursor to ethylene production. Application of Accede thus stimulates ethylene production which in turn triggers seed abortion and the formation of an abcission zone. Hence fruitlet drop (in apples when applied at 15-20 mm fruitlet diameter) and flower senescence (in peaches when applied at bloom) is promoted and accelerated. Application of ethephon can do the same thing, but ethephon is a bit “unpredictable” whereas Accede is a bit “safer.”

At the University of Massachusetts, Duane Greene started experimenting with ACC over 10 years ago. A couple years of trialing at the UMass Orchard in Belchertown on McIntosh apples resulted in significant fruit thinning that increased (less percent fruit set) with rate and with later timing (10 mm vs. 20 mm, Figure 1). He also noted some leaf yellowing/drop after Accede application, but it was not excessive. And Phil Schwallier at Michigan State University in 2016 showed that ACC application increased fruit size of Gala apples to 160 grams per apple compared to 120 grams per apple for untreated trees.

Figure 1 - 2011 results of ACC research at UMass Orchard (Duane Greene)

Lacking a state label in Massachusetts in 2021, I was asked by Valent to supervise Experimental Use Permit (EUP) applications of Accede in a handful of Massachusetts apple orchards. Valent applied for and received the EUP from the Massachusetts Department of Agricultural Resources (MDAR) in January 2021. Notable stipulations of the EUP included:

• MDAR notified in writing prior to application
• Supervised by Cat 49 (Research & Demonstration) applicator
• Public access limited by signage “Notice Pesticide Testing”
• Report submitted to MDAR at conclusion of EUP

With enough Accede on hand in the spring of 2021 to cover about five acres total, I solicited four Massachusetts orchards – one in the northeast, two in central Massachusetts, and one west of the Connecticut River – to use Accede under the EUP. I also intended to use Accede at the UMass Orchard in Belchertown. Along with Jim Wargo, Valent sales rep for New England and New York, visits were made to the orchards in late May to assess the need for further thinning after they had already applied their petal fall and 10 mm chemical thinners (Fig. 2). It was not too hard to settle on approximately one-half to one acre apple blocks where additional thinning was desired at 15-20 mm fruitlet size.

Figure 2 - Accede EUP application discussion with Jim Wargo (Valent USA) on 25-May, 2021

Valent supplied the directions for the growers to use when applying Accede under the EUP, including:

• Use a rate of 200-400 ppm (23-46 fl oz/A) at 15-20 mm fruitlet diameter
• Use a non-ionic surfactant at 0.05% v/v (6.5 fl oz/100 gal)
• Use 100 gallons per acre (adequate coverage of fruit and foliage)
• DO NOT apply as tank mix partner with other thinning products
• Consider reduced rate if temperatures predicted to exceed 90 F. on day of application
• And allow 7-10 days to observe effect of thinning

Growers were instructed to follow these directions the best they could, and applications were made around June 1. I should note that the NEWA Apple Carbohydrate model indicated a moderate deficit would be occurring shortly after most applications were made, so we expected to get some (good) results. Accede was applied to quite a few varieties, including Gala, Honeycrisp, Fuji, McIntosh, Cortland, Macoun, Golden Delicious, and Paulared (among a few others). Growers noted there were no particular problems mixing and applying Accede and most used LI-700 as the surfactant. The rate of Accede used was 300 to 400 ppm in 50 to 100 gallons of water. With the exception of Paulared and one Macoun block being larger trees, the rest of the blocks were smaller (150 gallons per acre dilute tree row volume approximately) but mature bearing trees on dwarfing rootstocks.

A few weeks following the Accede applications, a visit was made to each orchard to visually assess the efficacy (or not) of the Accede application(s). Valent provided a form that included the assessment parameters of leaf yellowing/drop, tree vigor, thinning activity, and return bloom (Fig. 3).

Figure 3 - Portion of assessment form provided by Valent to assess ACC applications

When assessments were complete, it was agreed that leaf yellowing-drop ranged from none to moderate, while tree vigor was generally good (slight reduction in canopy density) to excellent (no difference in tree canopy vs. untreated). Thinning activity varied widely by orchard and variety. As a general rule, Golden Delicious types (like Gala) were sufficiently thinned compared to the untreated control (Figs. 4 and 5) where little or no hand thinning was needed. McIntosh types seemed largely unfazed by the Accede application(s) though. This was also observed in an ACC experiment conducted on McIntosh by Greene where virtually no thinning occurred too. On Honeycrisp, it’s unclear how Accede may work, it may be useful there but still to be determined.

Figure 3 - Gala fruitlet drop following Accede application: untreated control on left vs. Accede application on right

Fig. 5 - Typical Gala fruitlet clusters after Accede application: untreated control on left, Accede application on right

We are learning how Accede may be another useful chemical thinner in your toolbox but don’t count on it being a silver bullet. Plan on starting chemical thinning early and often just as usual, and then bring out the Accede if you get to the point when fruitlets are 15-20 mm in size and you are looking at having to do considerable hand thinning still. Accede will probably not be a good option at the 10 mm fruit size, but that is still being evaluated. Having some carbohydrate deficit on the trees during the timing of Accede application will be helpful, and Accede may be particularly useful on Gala to increase thinning and improve apple size.

I alluded to the fact that Accede can also be used for thinning stone fruit, including peaches! That is a big deal as we don’t have a chemical thinner for peaches. And it’s a very promising thinner of peaches. For example, a summary of Accede EUP applied to peaches in 2021 in New York, Michigan, Ohio, and Pennsylvania across many peach varieties resulted in an average fruit reduction of 39% compared to the untreated control (Gregory Clarke, Valent USA). Peach varieties did vary quite widely in their thinning response to Accede, but that might have been a location effect. And in Michigan, work by Anna Wallis and Phil Schwallier in 2021 showed that hand thinning time was reduced by approximately 50% with Accede application compared to non-treated peaches. That would be sweet!

New York already has a state registration for Accede, on both apples and stone fruit, but as of late 2021 not all the New England states had Accede registered, including Massachusetts (per CDMS Advanced Label Search, which I really don't like, prefer Agrian, but Accede not listed there yet!). All state registrations, however, are expected in 2022. But I have learned that Accede supply for 2022 may be somewhat limited, and Valent plans to expand a demo program similar to what was done in 2021. Reach out to your agrochemical supplier if you want to use Accede in 2022, particularly if you want to trial it on some peaches.

Thanks to Parlee Farms, Carlson Orchards, Ragged Hill Orchard, and Clark Brothers Orchard for participating in the EUP. And to Jim Wargo and Greg Clarke of Valent for supporting the EUP in more ways than one. And Duane Greene for his preliminary work with ACC and for some worthy edits to the text herein...

Half-baked Research 2021: Part 2 - Lesson learned, don’t play with fire blight!

 Don’t play with matches. Don’t play with fire. Don’t play with fire blight! Lesson learned. Of course I had to prove it for myself, as in “Half-baked Research 2021: Part 2 - Lesson learned, don’t play with fire blight!”

I was approached in early 2021 by a notable “manufacturer and marketer of science-based nutritional and biological products that will enhance crop quality, storability, and yield in a profitable and environmentally sustainable manner” to evaluate some newer formulations as to how they might suppress fire blight infection. (Apple scab too with a different array of products, I will touch on that briefly at the end.) OK, I was game as I am a believer in their products.

The protocol called for product application(s) to apple at 1/2-inch green, tight cluster, 1st pink, and bloom with three of their products, at different rates and mixes, the idea being to build up some resistance to fire blight infection. At least that was the hypothesis. Treatments also included an untreated check (of course) and the grower “standard” of streptomycin at bloom.

OK. At first I proposed to do the work at the UMass Orchard in Belchertown, but as soon as it was hinted the trial might involve actual application of THE fire blight bacteria, I was promptly shot down by smart people at the University. Too much risk, too much time spent fighting fire blight in the past. Arghh, but I kind of understood and did not push the issue, despite it being a research orchard :-)

But, being stubborn, I said to myself, OK, I will see if I can find a grower cooperator. And darn it, if I am going to go to all that work to apply these products, I am not going to take the chance we actually have some natural fire blight going on, so I sure am going to inoculate the trees with ACTUAL fire blight when their time comes at bloom. I mean, how bad could it be? We know how to manage fire blight, right? I over-achieved and convinced (with some grumbling) two orchards to let me do the experiment within their bounds.

In one orchard, we agreed on a group of younger variety test trees grown to super-spindle on G.11 rootstock that were “mine” anyways. And the trees were on the edge of the orchard, and downwind from the prevailing wind. (Not that it does not blow from the East too.) I even suggested the trees were expendable if push comes to shove (literally) and they get a lot of fire blight. But I was not too worried, we could manage that, right? The second orchard had a couple rows of mature tall-spindle Fuji trees to work in, again on the orchard edge and downwind, that was great I thought, because it would be nice to have a real-world apple variety (vs. the numbered test varieties) to report the results to the sponsor. All was good, what could go wrong? 

So, the treatments (products) went on pretty much as scheduled. I used a back-pack sprayer, and they all got a good dose of treatments. A lot of driving around and work, but that was OK. Mission accomplished.

When bloom arrived in mid-May I made a run to the Connecticut Agricultural Experiment Station in New Haven to pick up some real live fire blight bacteria courtesy of Quan Zeng there. I think there was about 150 ml. of fire blight solution in an Erlenmeyer flask, the population density (CFU’s) of the fire blight bacteria in the solution escapes me, but I am pretty sure it was in the millions. I had to keep it cool (cold?) and use it in a few days, Quan advised. So, I put it in a cooler with an ice pack and safely seat-belt in the back of the Prius and set off back to the first orchard in MA to apply the fire blight. Somehow it felt pretty cool, definitely a first for me at least.

When I arrived to apply the bacteria, the test trees were in a varying state of bloom, and it was not as warm as predicted, maybe 65 degrees whereas it was supposed to be in the 70’s. Damn unpredictable East wind! But I went ahead and applied the fire blight bacteria solution to open bloom using the backpack sprayer. I should say I tagged only an individual limb area of the trees to direct the fire blight spray, I did not spray the whole tree with fire blight! After applying the fire blight to all the treatment trees I followed up with the streptomycin treatment to those trees only dedicated for that treatment. Because it was so cool during the application, and some of the test varieties did not have much open bloom yet, I came back a few days later as I had some fire blight solution left. So I sprayed the trees again with the fire blight even though it was even cooler and it started raining during the application!

Fire blight application to the Fuji orchard was a bit less dramatic, conditions were pretty good, with temperatures in the mid-70’s and a bit of humidity. That application was made mid-week (in mid-May) between the two applications described above.

I had some trepidation about whether the fire blight applications would work, for several reasons. Mostly because the application conditions were not ideal (too cool?), and I was afraid I might have not treated the fire blight containing flask 100% as recommended – maybe kept it too cold, maybe took too long (four days) to get the application(s) made?

So. I waited. Told the growers to let me know if they saw any sign of fire blight. I waited. A week. I was depressed. Doomed to fail. But then, shortly after a week, I got the first call, “yup, seeing some fire blight there in those variety test trees, you better get out here to take a look!” I did, and it was indeed fire blight! Yippee! And then guess what? A few days later, I got a call from the Fuji grower, “I think I am seeing some fire blight, you better come have a look.” Oh yes, a touch of fire blight. No worries, it did not seem too bad. So we waited a few more days.

Then things got worse. Fast! The fire blight was taking off! I had to get to both orchards and do my treatments evaluation, which was a simple rating scale – 0 = 0%; 25 = 25%; 50 = 50%; 75 = 75%; and 100 = 100% fire blight of flowers infected – on the limb area where I applied the fire blight. Done. And some pruning out of blight by me. But, it continued to get worse in both orchards, and some fire blight spread to neighboring trees was observed. Result was some sleepless nights, at least by me! We were resigned, however, to manage it (and the spread) by cutting it out (for a while) and spraying some low rate copper (in a Double Nickel/Cueva combination) and Apogee to the infected (including adjacent) trees. Some Oxidate too.

And then, a bit of miscommunication resulted in the demise of the experimental variety block! That was OK, as we had agreed on this course of action, but I was a little disappointed we did not try to further manage it. It was, however, spreading to adjacent Honeycrisp and Evercrisp trees, so totally understandable. It was the end of two experiments as you can see…

Grower impatience leads to the demise of the
fire blight infected apple variety test block! (25-May, 2021)

As to the Fuji block, heck now, we were not going to cut that one down! So, we fretted, and continued to prune out the fire blight. Some of the treatment trees were looking pretty sad (cut up), and there was some spread to adjacent Braeburn, Gala, and Honeycrisp. Finally by mid-summer the worst was over, new fire blight infections had stopped, and the block was salvaged I think. Can’t say the grower was overly happy, but he remained pretty good-natured about the situation. He is going to have to be on top of it in the Spring of 2022 as I am sure there are plenty of cankers left there. I don’t believe the fire blight killed any of the trees outright, despite being on susceptible M.9 rootstock.

So you probably gathered by now the products tested were not overly effective at preventing fire blight. Correct. But in retrospect, I don’t think the intent was for these to “prevent’” fire blight when disease pressure was extreme, as it was with my generous blanket of fire blight bacteria sprayed on the trees during bloom. I believe the idea was to solicit some kind of SAR (Systemic Acquired Resistance) response, which may or may not have happened. (Don't dismiss the nutrition benefits of the products either.) Worth pursuing with further research? Probably. Oh, by the way, I said the treatments did not “work.” Actually one did, guess which one? Yup, the streptomycin treatment, which was nearly 100% effective at preventing fire blight infection. Should we be surprised? Probably not, streptomycin is very effective at reducing the fire blight bacterial load and preventing infection. (Unless resistance to strep by the fire blight bacteria has developed.)

I failed to mention I also did apply the fire blight treatments to a group of Honeycrisp trees at the UMass Orchard, but I did NOT spray with fire blight bacteria. Guess what? Absolutely no fire blight. Same (mostly) for the rest of the Orchard. And oh yes, I mentioned I also worked with some purported apple scab suppressing (at least that was the hypothesis) products at the UMass Orchard, on McIntosh trees (highly susceptible to scab). These again were nutritionals/biologicals, I did not expect much, and that was the case. High rates in one case caused some phytotoxicity – they got a good dose multiple times coinciding with change in bud stage and/or primary apple scab infection period – and that actually inhibited scab because the phyto was so bad there was less susceptible green tissue. BTW, the control there was primary apple scab season-long Inspire Super. I don’t recommend it nor does the label advise it (resistance issues), but there was no scab, it works… :-)

Fuji fire blight experiment trees approaching bloom on 4-May, 2021

Blossom fire blight infected limb on experimental tree (22-May, 2021)

Thank you Tougas Family Farm (Northboro, MA) and Outlook Farm (Westhampton, MA) for the extra work and stress I created while doing this “half-baked” research. And to the sponsor for their financial support…

“Half-baked” Research 2021: Part 1 - “Precision” Crop Load Management

2021 was a year of – how shall I say it? – “half-baked” research. With a couple exceptions, too many minor research projects producing variable (aka dubious?) results. But I like to document “stuff.” So I am going to write up some “research” I did during the 2021 growing season for “what it’s worth?” (Hopefully something!) So here is “Half-Baked” Research 2021: Part 1 - “Precision Crop Load Management.”

In April 2021, in a commercial orchard “we” (meaning the grower and I) attempted to initiate a full-fledged research project per a protocol developed by the PACMAN group. PACMAN being “Precision Apple Crop load MANagement,” or as some prefer to call it Precision Crop Load Management (PCLM) of apples. The protocol was developed to address Objective 1. of PACMAN - “Develop and disseminate user-friendly computer-based models and comprehensive crop load management strategies for apple to achieve optimal crop load and maximize crop value.” Real PACMAN researchers in WA, MI, NY, NC, and VA are also following the protocol(s), which basically are as follows:

• For Experiment 1 – Pruning treatments: At green tip, reduce the total number of spur floral buds per tree to 50, 100, 150, 200, 250, 300, 350, or 400 with a target of 8 trees at each level. Thinning treatments: 1) Hand thin at full bloom to 2 flower per cluster then thin to single fruitlet (largest) at 10mm fruit size, 2) Chemically thin at bloom with lime sulfur and fish oil guided by the pollen tube growth model, at Petal Fall with NAA+Sevin and 12mm with Maxcel+Sevin if needed. Data collection to include: TCSA, final floral bud number per tree at bloom, final fruit number per tree at harvest, yield, average fruit size, average fruit red color, either actual packout (size and color) or calculated packout from mean fruit size and mean color and using a normal distribution to estimate number of boxes per acre in each size and color category.
• For Experiment 2 – At green tip, reduce total number of spur floral buds per tree to 200 on all trees (2 times the target fruit number of 100) The pruning must be done at green tip when floral spur buds can be easily distinguished from vegetative buds. 4 levels of crop load (3, 6, 9, and 12 fruits/cm2 TCSA). At full bloom reduce the number of clusters per tree to the assigned crop load (assuming only 1 fruit per cluster) by removing all flowers of a cluster. Secondly reduce the number of flowers per cluster to 2 (king and L3 lateral flower). Thirdly, at 10mm fruit size reduces the number of fruits/cluster to the desired crop load by hand thinning leaving only 1 fruit per cluster (the largest fruit). No chemical thinning.

All sounded like a good idea. On paper at least. But after thinking about the whole thing longer – and after flagging experimental trees, and starting to follow the protocols – we realized, amongst all the six million other things we had to do during the spring, and all the other projects I had going on (more on all that with upcoming blog posts) we simply could not follow through with all the treatment and data collection protocols. So, what actually happened?

The pruning treatments (Experiment 1) were accomplished on Gala trees. (Despite some grumbling by the grower.) Grower chemically thinned, however, pretty much at will. Farm crew avoided (I believe) hand thinning our flagged treatment trees. In September, we (thanks Jim Krupa) counted the number of apples remaining on the flagged treatment trees across eight replications. Observation of the pruning severity treatment trees was interesting, and we all agreed we liked the look of the Gala apples on the 50 and 100 buds left after green-tip pruning. At the higher bud densities, the Gala apples were “small.” Although the grower said – being a pick-your-own operation – the more apples the better. They agreed, however, they want quality, good-tasting apples for their customers, something they hang their hat on, and aggressively attempt to manage crop load for quality and annual bearing. Want to see the results of the fruit count per tree (across 8 trees per treatment counted) at harvest?

If I were to plot that, because we, as scientists, that’s just what we do, make charts:

Not a bad “fit.” (Red line.) Where is the sweet spot? I think where 100 meets 100, i.e., prune to a bud load of about 100 buds, hope for one apple set per bud, equals 100 apples per tree at harvest. Hope. Maybe best to leave a few more buds to hedge  your bets. Picts of the different pruning treatments vs. crop load at harvest follow at the end. You be the judge.

Oh yea, Experiment 2, we did not follow through much at all. Well, the grower did attempt to reduce the 4 levels of crop load – to 3, 6, 9, and 12 fruits/cm2 TCSA – per the protocol, but only on a few reps. These were Honeycrisp trees BTW. Did not see much going on there in the end. We did some fruit counts at harvest. I won’t ever report that because there is nothing there. Half-baked? Yup.

In the Gala experiment, I do think we learned something – that we may be under-pruning if the goal is large Gala’s. We kind of knew that, but this little bit of work bears that out. It will be very interesting to see the results from the real research, but I do know a preliminary analysis of the data suggests that “at a given crop load, larger fruits are produced in some climates than in other climates.” (2021 PCLM Report, T. Robinson et. al.)

Thanks to Tougas Farm for letting this research happen (despite some grumbling) and to Jim Krupa of UMass who so aptly helped me count apples and and held the treatment flagging for the pictures!

Pruned to 50 buds, 71 (large) apples left at harvest

Pruned to 100 buds, 140 apples left at harvest

Pruned to 150 buds, 122 apples left at harvest

Pruned to 200 buds, 148 apples left at harvest

Pruned to 250 buds, 140 apples left at harvest

The 2021 apple pest season according to the RIMpro Cloud Service

Directly from their website "RIMpro Cloud Service is an interactive Decision Support System (DSS) for pest and disease management in fruit and wine grape production. For many growers and consultants RIMpro is their essential tool for effective crop protection." We have been using RIMpro for some years now, and although not for everyone - NEWA being a good alternative - it is the most sophisticated and granular DSS out there. Visual presentation of model output  - such as the the flagship RIMpro Venturia (apple scab) model - is a particularly good and useful feature of RIMpro. To that end, I present mostly -- with a little explanation - the graphical RIMpro model output for most of the important apple pest model outputs of RIMpro, including Venturia (apple scab) for the 2021 growing season at the UMass Orchard in Belchertown, MA...

Apple scab model output based on weather station. Only when the red line (infection value) exceeds 100 is the scab risk high in an otherwise "clean" orchard. Thus, five apple scab infection periods that would need fungicide coverage, probably a combination of protectant and kick-back fungicides. I'd be looking at six sprays maybe?

Apple scab model output based on virtual (meteoblue.com) weather data. Whoa, big difference from onsite weather station. Here, nine RIM values exceed 100 (Medium infection risk) which would trigger at least nine fungicide sprays? The virtual weather data appears to over-estimate when it rains (or not).

Apple powdery mildew. Not clear on how to interpret, but it looks “bad!” Yes, powdery mildew was an issue this year on susceptible varieties like Cortland and Honeycrisp. Really. Pretty. Bad.

Fire blight. According to this RIMpro output there was one actual fire blight infection on May 18th wherein first visual symptoms should appear about May 25-26. A streptomycin spray then should have resulted in no fire blight. This is confirmed at the UMass Orchard. Plenty of fire blight around elsewhere though, interesting…

Moving on to an early insect, rosy apple aphid, the little buggers. The way I interpret this, nymphs and adults are in abundance and not yet curled up in the foliage during a tight spray window of approximately the last week in April into the first week of May. Two weeks. Indeed, this was overlooked and RAA was a real problem in certain orchard hot spots. Bad, trust me, resulted in many stunted/deformed apples.

Another early insect, apple sawfly. RIMpro shows May 11 as a recommended insecticide application date. This was during the early petal fall period, which can be problematic. Fortunately, sawfly seems to be a significant problem only in loosely managed orchards, in most it is not an economic issues. Of course you can see there is also activity pre-bloom, so a pre-bloom insecticide is also an option, although most would say not a good option.

Codling moth. Pretty straight forward if targeting hatching eggs and L1 larvae with an insecticide, for first generation about June 20, and for second generation (if necessary) in mid-august.

Codling moth using virtual weather data (even though I said I was not going to bring it up again). But, as the codling moth model only uses degree days to calculate CM life cycle, it is much better than when using wetting information in a disease model. Here, the CM insecticide spray windows largely agree with spraying dates using the on-site weather station.

Ah, some horticulture, apple thinning, only available when using the meteoblue weather forecast (virtual data). Pretty busy chart, eh? Let me just point out that app. May 23 and then again on May 27 there were  modest carbohydrate deficits, which would have been good chemical thinner application windows if you expected those chemical thinners to work. The growing pollen tube growth/squiggly blue lines also presumably help you time caustic bloom thinner application, but who does that anyways?

Sooty blotch/flyspeck. Who cares? All I know, is that in addition to preventing rots — that is another story this year — you need to be applying fungicide every 10-14 days (assuming it rains an inch or two during that time, no problem with that this year) beginning late June right up to harvest (following PHI’s of course). Watch late varieties in particular with moderate-severe infection events ins September-early October.

Marssonina leaf blotch. An increasingly vexing problem, seen plenty of it at the UMass Orchard beginning in mid-September, Golden Delicious, Mutsu, Fuji, Honeycrisp, Pazazz, and Topaz. Among others. Macs seem pretty immune to it. A fungal disease similar to scab, however, requires season-long control. Getting lax with late season fungicides can cause early defoliation, not sure how bit a problem that is? Can cause fruit spotting, but have not really seen that yet, stay tuned? RIMpro output suggests many infections, indeed that was the case I think…

Yes, we got apple scab in 2021 on unsprayed trees

Fresh apple powdery mildew!

Oh yes, there was fireblight, none at the UMass Orchard, but sporadically/widespread elsewhere!

Rosy apple aphid (RAA) nymph on apple bud in early April

Deformed apples in early July a result of RAA infestation

Marssonina leaf blotch on Evercrisp in late September

By late October (harvest time) these Evercrisp were completely defoliated a result of Marssonina leaf blotch!

Double-notching whip apple trees at bud break effective at promoting branching

Nursery apple trees that arrive as unbranched, so-called “whips” are a perpetual problem. In the old days, when growing a central-leader tree, those whips were simply headed (cut) at waist height and then a lower tier of scaffold branches would result from buds breaking and shoots growing (feathers) vigorously just below the heading cut. Then some of those would have to be “stripped” off so a proper leader could form (http://fruitadvisor.info/tfruit/clements/articles/youngtreetraining.htm).

But if a tall-spindle system is being planted, that heading cut is a big no-no, you don’t want strong vigorous shoots growing that form permanent scaffold branches. Unless the nursery tree comes already feathered, it’s nice to get numerous smaller branches “breaking” along the length of the leader starting at approximately knee height and moving up the leader. What typically happens on whips, however, is only the top buds break going a foot down or so from the top of the leader. In addition to ending up with a top-heavy tree, those shoots will flex their apical dominance and further prevent lower buds from breaking. So, intervention is desired on newly planted whip apple trees to get the uniform branching up and down (to knee height) the tree and create the desired tall-spindle form early and going forward.

Several techniques can be used to induce this kind of branching. A common recommendation is to spray the leader with 6-BenzylAdenine (6-BA) at bud break. 6-BA formulations include Promalin or Maxel (Valent) and Exilis or Perlan (Fine Americas). Over the years, I have found this to not be particularly successful at inducing branching (http://umassfruitnotes.com/v75n3/a3.pdf). Dormant buds along the leader can also be painted with a high concentration of 6-BA in latex paint but this must be done before bud break. It is largely successful but can stunt the growth of the resulting shoots (http://umassfruitnotes.com/v79n3/a2.pdf; http://umassfruitnotes.com/v80n1/a2.pdf; http://umassfruitnotes.com/v85n1/a6.pdf). Notching of the leader just above the bud where a branch break is desired can be effective, however, it is time consuming when using a hack-saw blade as has been often recommended. Recently, I’ve become aware of using a double-edged, anvil-style hand pruner making two opposite side “notches” just above buds in the region where branching is desired (Stefano Musacchi, WSU, personal communication). I have previously tried this here and there and my observation was that it does indeed appear to be quite effective. So, in 2021 I decided to do a mini-experiment to demonstrate this method of inducing branching on whip nursery apple trees.

Methodology was quite simple, I selected 30 just-planted whip apple trees at the UMass Orchard in Belchertown, MA. In a random manner, ten of the trees were NOTCHED using a double-edge hand pruner (STA-FOR Double Cutting Pruner, https://www.oescoinc.com/hand-tools/hand-pruners/double-cutting-pruner.html) just above each bud in the region where branching was desired, i.e. from approximately knee height then upwards about 18 to 24 inches. Typically, eight buds (plus or minus) were thus double-notched. This was done just as the buds in the top of the trees were breaking, but the dormant buds that were notched showed little or no growth (yet). 6-BA in the form of Promalin per the label rate (400 ppm) and directions for promoting branching at bud break was also applied to a similar region of the leader on ten other trees, and ten trees were left alone (the UnTreated Control, UTC).

In mid-June, the number of branch breaks (greater than 2.5 inches in length) on each tree in the region the branching treatments were applied were counted, and the results speak for themself. NOTCHED trees averaged 8.5 “breaks” per tree that are becoming feathers or branches. Nearly every notched bud broke and grew into a feather. 6-BA way underperformed compared to notching, with only 1.9 breaks per tree, and the UTC only resulted in an average of 0.8 branches per tree. (If you insist, a statistical analysis was done on the data, and the difference in branching was significant, and the NOTCHED treatment resulted in significantly more branching than the 6-BA and UTC treatments, which did not significantly differ from each other.)

Clearly notching using this double-edged anvil-style pruner is effective, and making the notches using the pruner is reasonably quick. Care must be taken, however, to not cut all the way through the tree nor to girdle the tree. (Someone suggested angling the pruner a bit to lessen the risk of girdling.) For several hundred newly planted trees that are whips it sure beats getting out the 6-BA filled backpack sprayer or the paint mixed up with 6-BA asNOTCHING in this manner is very effective at making branches. You do of course need to have a viable bud where the notch is made, and it is not alone effective at breaking branches on older “blind” wood without further intervention (http://umassfruitnotes.com/v82n3/a2.pdf). Furthermore, 1st-leaf trees should be planted early, fertilized, and irrigated to get the most out of your notching effort.

Here is a YouTube video about this mini-experiment: https://youtu.be/x2EqTUTBhFc

NOTCHING just above a dormant bud using a double-blade anvil style pruner

NOTCHING resulted in 8.5 feathered branch breaks per tree

6-BA application resulted in an average of only 1.9 feathered branch breaks per tree

UTC (no intervention) resulted in average of just 0.8 feathered branch breaks per tree

Fire blight's ugly side...

Blossom blight on newly planted NY-1 apple tree

Does it have a pretty side? No, of course not. But this past week I saw a particularly ugly side of fire blight.

First up, this year's planting of NY-1 (sold as SnapDragon®) apples. Serious fire blight taking out significant portions of the leader, maybe up to 50% of trees planted. Sorry sight. Conversation with grower:

Grower: "Did it come in from the nursery?"

Me: "Nursery will deny it and in reality you have a mature apple block next door with a history of fire blight and these affected trees had a lot of bloom, right? Did you remove the bloom or spray streptomycin during bloom?"

Grower: "No on removing the bloom, but I did spray strep once, and there was no rain when they were in bloom."

Me: "Yea but I checked NEWA and indeed the fire blight risk was high to extreme and it does not take much wetting, for example airblast spraying or heavy dew, to spread the blight around and cause infection."

Grower "Oh, now what can I expect?"

Me: "Well you are cutting the fire blight out during dry weather to the best of your ability, it is a shame given many trees have significant part of the leader with blight, and some trees will have to be removed completely. And you will continue to see more blight after you think you have it all cut out. You should probably also spray copper as often as feasible, that will help reduce the spread. And next year be on top of bloom with strep sprays when the fire blight risk is high. Hopefully infection will subside now which is usually what happens after the initial outbreak, but it won't go away unfortunately."

Grower: "But I still think it came in from the nursery :-)"

OK, questions lingering in my mind after departing the orchard. Is SnapDragon® particularly susceptible to fire blight? I know for a fact it's sister NY-2 (sold as RubyFrost® apples) is very susceptible. And a couple other adjacent just-planted varieties (MAIA apples) had some, but not nearly as much, fire blight. And, I know there are other recommendations out there to help prevent further spread in young trees, what are those? Double Nickel and Cueva? Actigard and Prohex-Cal (Apogee/Kudos)? But of course I did not remember the details.

Second, another new planting, this time MAIA-1 (sold as Evercrisp® apples), orchard crew in the middle of once again cutting it out. Enough to be time consuming, will never get it all, and in some cases the whole leader blighted. Ugh. Was not easy to elicit whether strep sprays had been applied, maybe just once? Now I was getting mad after seeing this twice in one week, and it seems to me this could have been prevented? Or maybe not given the fact this new apple planting was adjacent to a block of cider apples! Now there is double trouble if I ever saw it! A history of fire blight in this cider block, of course. Found some blight over there right now, Dabinett, Stokes Red had more than most of the others. It's just not a good idea planting a new apple orchard next to a cider apple block! (Is it a good idea to plant cider apples period? I am beginning to wonder...)

Shoot blight (likely originated from blossom) of 1st-leaf MAIA-1 apple tree

Bin full (literally) of fire blight prunings

Fire blight in cider apple (Dabinett or Stokes Red)

OK. What could have and should be done to prevent or reduce fire blight infection on these 1st-leaf trees:

• Manual removal of bloom. I know, it is time consuming but probably the number one thing you can do to prevent blossome blight infection. Usually requires several trips, every other day or so through the orchard to get all the bloom. I just clip the flower petals off at the pedicels with scissors or similar.
• Lacking bloom removal, frequent strep and copper sprays, as recommended by consultant Win Cowgill. Copper beginning at bud break, your choice of product at moderate rate. Streptomycin beginning when first blooms open and continuing every 2-3 days as bloom opens. Need several (many?) strep sprays to keep up with open bloom. Until it is done. Strep probably not necessary if it is absolutely dry and there is no risk of fire blight infection predicted by the models, but that is rare. I know there are peaches to prune and vegetables to plant but you need to find time to do this! And think about coverage, there is not much tree there, turn off the fan, go slow, make sure you are getting good coverage and not blowing your spray all over the place!
• If you are not successful with above, yes, cut out the fire blight. In dry weather. Does not hurt to sterilize pruners between cuts unless it signficantly hinders speed of fire blight removal. Goal should be to get it out of there ASAP. Remove prunings well away from orchard if possible, otherwise put in middle, let dry out for a few days, and mow. Always during dry weather.
• After pruning, it looks like the best option to prevent further shoot blight are regular applications (every 1-2 weeks?) of Double Nickel (a biofungicide) and Cueva (a low rate copper). There are other "biologicals" out there, but the Double Nickel/Cueva option seems to have the most mentions and has proven to be the most effective at preventing shoot blight. Kari Peter at PSU has a good review of these options here. (I wonder about Oxidate? Couldn't hurt.) And oh yes, a strep application if a trauma event -- rain with high wind and/or hail -- occurs.

Finally, be on top if it next year. George Sundin at MSU recommends Actigard with Prohex-Cal on young trees (2nd and 3rd-leaf) at high risk for fire blight. And strep during bloom when the fire blight warning flag gets hoisted is still your best friend.

Fire blight prediction models — words and colors (and numbers?) matter

This week apples have been in bloom in Massachusetts. Along comes the risk of fire blight blossom blight. Warm temperatures and moisture are known to be the trigger for blossom infection by fire blight. It’s been relatively cool — 60’s to lower 70’s — so the apparent risk of infection has been perceived as low. In addition, we have fire blight models on NEWA (Network for Environment and Weather Applications). And they — both Cougar Blight and the EIP (Epiphytic Infection Potential based on the MaryblytTM model) were showing generally low risk for blossom infection by fire blight. Nice, breathe easy, right?

But wait, there is always a catch when it comes to dealing with fire blight. A grower, who has a history of fire blight in their orchard, called me in the afternoon and said something to this effect, “Jeez Jon, this morning NEWA was showing low risk of fire blight infection but now one of them is green (Cougar Blight) and the other (EIP, Maryblyt) is showing HIGH, ORANGE risk of infection. What gives? Do I need to spray streptomycin? Arghhh, I had just put a cover spray on for scab this morning but did not include strep and I really don’t want to have to go out and spray the whole orchard again to prevent fire blight, what should I do?”

Great. Begs many questions. For one, I told the grower I am never going to tell him definitively NOT to spray strep for fire blight! But seriously, the day turned out warmer (low 70’s) than predicted (mid 60’s) so the model output changed. But why the perceived difference (by the grower) in model outputs, Cougar Blight being GREEN (low risk of infection?) while the EIP was ORANGE signifying much greater risk of infection? I was unable to give them a clear answer, so I had to do a little digging to refresh my memory on how the models differ in estimating risk of infection. I want to say here, however, the user-interface (on NEWA) is not the best and I hope my discourse might result in some clarification of the fire blight model outputs on NEWA going forward? Kerik?

OK, all a grower needs to know about the two fire blight models on NEWA, Cougar Blight and EIP.

Cougar Blight simply accumulates degree hours as heat units beginning at bloom. Then, models the fire blight infection risk level based solely on these accumulated heat units/degree hours. Note that it does NOT use wetting or anything else in determining risk, you have to assess the level of wetting's contribution to fire blight infection, be it rain, dew, spray event, etc. But if Cougar Blight says the risk is HIGH or particularly EXTREME you better be applying some streptomycin to open bloom if wetting occurs. Note that the infection risk level also changes based on the amount of fire blight recent history in the neighborhood. Generally I leave it as fire blight occured in the neighborhood last year to keep it middle of the road unless I know fire blight is currently active. Very simple, but realize the Cougar Blight model can say HIGH or EXTREME but if there is no wetting event, there will be no infection. Here is the latest on Cougar Blight from WSU, but realize they talk about wetting event in their DAS which is not included in the NEWA Cougar Blight model. 

EIP as I said is straight out of the MaryBlyt model. Which is way more complicated than Cougar Blight! (Which makes it better? Maybe?) I will try to boil it down to as simple as possible. For a blossom blight infection to actually occur, regardless of whether EIP/Maryblyt shows up YELLOW or ORANGE, four condidions must be met:

1. open bloom (D'oh! as Bart would say)
2. degree hours/heat units accumulation threshold
3. average (daily, 24 hours) temperature greater than or equal to 60 degrees F.
4. AND wetting! one tenth of an inch or more of rain, or could be heavy dew or dilute spray event?

INFECTION will not occur unless all four of these conditsion are met. Just one, two, or three of these conditions might indicate LOW, MODERATE, or HIGH risk of infection, but you would still need the fourth parameter, likely wetting, for INFECTION to actually occur and eventually show up as blossom blight. Below is a Table -- straight out of the 44 page Maryblyt manual, available here -- that pretty much sums it up:

Ok, let's look at the NEWA fire blight model ouptut that triggered this blog post:

The afternoon in question was 5/3, this model output was run after the fact, and actually at the time on 5/3 Cougar Blight was showing a GREEN table cell. You can see why the grower might have been concerned, not understanding the nuances of the models, a GREEN-Low infection risk cell table in Cougar Blight, and an ORANGE-High infection risk in EIP (Maryblyt). Huh? Admittedly, NEWA does, below the Table provide this explanation: 

Somewhat helpful but not overly, especially if you are panicking trying to figure out if I should apply a strep spray or "Oh crap, how come I did not include strep in that scab spray I just put on this morning???" Really, I told the grower it was in fact borderline and forecast cooler temperatures might reduce the risk of infection significantly. They still went out and sprayed streptomycin on younger, more susceptible blocks, or maybe it's been rumored they sprayed the whole orchard! Was there actually an INFECTION? Probably not, no, it appears not all four conditions were met for an INFECTION to occur. Bloom? Check. Degree hours? Check, barely, briefly, but then went down the next day 5/4. Wetting. Check, but not until next day 5/4. Average Temperature? Check, but only for 5/3 and barely. NO INFECTION! No need to spray strep! If you have faith and believe the models are right?

My thought is growers really need to know that all four conditions -- bloom, degree hour accumulation, average temperature, and wetting need to be met for an INFECTION to actually occur. This again in the Maryblyt manual is helpful: "A blossom [strep] spray is recommended when the risk is HIGH and when an infection is predicted for the next day."

Oh, and then there is RIMpro...

Whew, not sure I really cleared anything up or simplified it or not? Note to self, stick with horticulture, want to talk about thinning sprays now??? :-)

Tree Row Volume - it doesn't matter.

A recent New England Tree Fruit Extension Seminar focused on Tree Row Volume (TRV): What it is, why it matters, and how to use it. (You can watch the recording here when it becomes available.) After a brief introduction about TRV by the host, a guest speaker -- Jason Deveau, of sprayers101.com fame -- cut to the chase about what (IMHO too) is really important, that is spray COVERAGE. Because, modern pesticide labels make no mention of TRV or rate per 100 gallons, a rate that was based on dilute spray coverage using TRV. Forget TRV, just worry about getting good coverage with an adequate amount of water. Then apply the amount of pesticide per acre as noted on the label in that amount of water that is getting you good coverage. Bingo.

I am not going to talk about how to get good airblast sprayer coverage here. For that you need to get your copy of sprayers101.com/airblast101/. But let's look at a scenario. Let's say you have a tall-spindle apple orchard. Using TRV, it calculates out to about using 100 to 125 gallons of water per acre that would give you really good coverage. Fine if you are spraying oil. But when not, most growers I know spray tall-spindle using 50 to 60 gallons per acre and get quite adequate coverage. Adequate is fine because you can only fill up the sprayer so many times, right? There are other things to do!

OK now, let's look at a very modern pesticide label, that of Valent's Excalia. For apple scab, it says use 3 to 4 fluid ounces of Excalia per acre in a minimum of 100 gallons of water per acre. (Interesting on the minimum 100 gallons of water per acre, that is unfortunate, I would ignore it and as long as you are getting good coverage -- the label says "Equip sprayer with nozzles that provide accurate and uniform application" -- you should be fine.) So, if your tall-spindle orchard has a little smaller trees or pest pressure is on the lower side, use 3 ounces of Excalia in that 50 to 60 gallons of water. Alternately, if pest pressure is high and trees are just a little bigger, use 4 ounces. Simple. You got good coverage and are applying the label-correct amount of pesticide per acre. Modify this train of thought accordingly to your tree size/acreage/pesticide label. Point is to get good COVERAGE with the label-recommended amount per acre of pesticide.

One little monkey wrench thrown into this thought process might be when using Plant Growth Regulators (PGR's). Because, their label rate typically DOES NOT use rate per acre, but instead amount per 100 gallons (dilute TRV). (Or even worse, Parts Per Million (PPM). Ugh.) Don't stress though. Let's look at NAA in the brand name PoMaxa. The label says to use 1 to 4 fluid ounces of PoMaxa in 100 gallons (TRV) for apple thinning. So my tall-spindle orchard, to keep it simple, requires 100 gallons per acre TRV. So if I wanted to use a 4 ounce rate (equivalent to 10 PPM) I would need 4 ounces of Pomaxa in 100 gallons of water to cover that acre. But I am using 50 gallons to cover an acre, so I still need to add that 4 ounces in the 50 gallons of water, right! (Which is now technically equivalent to a 20 PPM solution, isnt' it? Why I don't like PPM.) Interestingly again, in the text of the label, it says "A typical rate for a moderate-to-thin apple cultivar in an orchard which requires 100 gallons of water per acre to achieve drip is 2 fl oz of PoMaxa per acre. For an acre requiring 200 gallons to achieve drip, use at least 4 fl oz per acre." Makes perfect sense, doesn't it? So why not just say that on the label and leave it at that! My advice would be for apple thining to say "use 2 to 8 oz. per acre depending on tree size and amount of thinning desired!" That would cover most dwarf and semi-dwarf orchards. And that is what I tell growers! For more on this topic: Spray Mixing Instructions (for PGR's) Considering Tree Row Volume

So, even though my start-out premise was TRV is dead, I came about and with PGR's not so fast! Sorry about that. I still contend, however, focus on getting good COVERAGE. Then for fungicides and pesticides use the label rate per acre, adjust the amount of product based on tree size and pest pressure. But always within the label amount (minimum and maximum) per acre. For PGR's, put on your thinking cap, analyze the situation a bit, and convert the label recommendation, whether it's amount per 100 gallons TRV or PPM, to rate per acre. Small trees, less PGR per acre, large trees, more PGR per acre. Less efficacy -- need for less thinning for example -- less PGR per acre, more efficacy, more PGR per acre. Makes kind of common sense doesn't it?

Still want to calculate TRV?