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…