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bicarbonate for thinning

Posted by Brian Caldwell 
bicarbonate for thinning
December 05, 2012 08:57PM
There is a very interesting article from Europe on using bicarbonate for thinning. It might be a reasonable alternative to lime sulfur/oil, which raises phytotoxicity concerns with me. Since I use sulfur for scab and occasional lime sulfur, I don't want to burden the tree with more LS. This thinning article is in the HON library.

Since we got virtually no crop this year, I expect next spring's bloom to be heavy. We'll probably need to thin heavily!

Hemlock Grove Farm
Zone 5 in New York

Edited 1 time(s). Last edit at 12/07/2012 08:38AM by Michael Phillips.
Re: bicarbonate for thinning
April 19, 2013 08:18PM
First, dont use Armicarb. Get a technical grade potassium bicarbonate (2,65$ a kilo).

Test have shown that Armicarb causes more phytotoxicity then the technical grade product. Go figure.

Second, I tried it, probably a bit too late and got little results to show for.

This year, I expect a heay crop so I will be using Lime sulphur like a mad man!

7 acres in Oka (Qu├ębec)
Certified Organic Orchard
Sunrise, MacIntoch, Spartan, Cortland, Empire,

Edited 1 time(s). Last edit at 06/04/2013 09:17PM by Michael Phillips.
Re: bicarbonate for thinning
May 10, 2017 10:56AM
I was wondering if anyone has an update on using potassium bicarbonate for blossom thinning? Brian tells me his team has put on a couple sprays of Milstop @ 12.5 lb/100 this past week and really fried some petals! The big unknown when you take out subsequent bloom (following reasonable king bloom pollination) is how this truly plays out with fruit set. Two years back Brian felt he had really overdone it with his Goldens but then the apples sized up nicely and it indeed proved to be a proper crop.

Two other approaches used in Switzerland jumped out at me in reading that research paper anew but I can only speculate how these work as blossom thinners. Using ordinary foodstuffs has a certain appeal:

Molasses, applied 2 to 3 times, at 5 to 7% concentration . . . excess sugars overwhelm the bees? More likely gunks up the works, eh?

Cider Vinegar, applied 2 to 3 times, at 3% concentration . . . does acetic acid fry fragile flower parts? This might even have relevance for fire blight, given vinegar's anti-microbial oomph. Good use for a batch of vinegar gone awry.

Anyhow, it would be great to hear actual bicarb results from those of you who have tried this in past seasons. I' m tempted to go with ordinary baking soda, aka sodium bicarbonate, Arm & Hammer brand, costing as little as $8 for a 12 pound box. The base rate is the same, 10# per hundred gallons, along with one ounce of Therm-X as a sticker. Varieties like my Sweet Sixteens are loaded with blossom buds, and spraying half of those dozen trees will make an effective trial. The need to thin will very much tie to it warming up next week and bees of all persuasions flying in earnest.

Lost Nation Orchard
Zone 4b in New Hampshire

Edited 1 time(s). Last edit at 05/14/2017 12:04PM by Michael Phillips.
Re: bicarbonate for thinning
May 10, 2017 01:33PM
I will check in with other organic growers in our club.

Re: bicarbonate for thinning
May 11, 2017 06:29PM
Trying regalia + oil at several locations for thinning and CAR. Burned lots of petals, but nothing def yet. Will update when we have some details.

Mike Biltonen, Know Your Roots
Zone 5b in New York
Re: bicarbonate for thinning
May 14, 2017 12:42PM
I'd also be interested to know how potassium bicarbonate does in blossom potential. One theory holds that the freshly-exposed stigmas are somehow damaged, thereby blocking the gateway by which pollen reaches the ovules. High pH could alter stigma receptivity by no longer supporting pollen hydration and thus the formation of a pollen tube. Brown flower petals might deter bees but I don't think it's that simple. Russeting is said to be an issue if it rains within 24 hours of application. Not sure how temperature fits in here.

First app is made at about 10 to 20% bloom, following a day or two of decent king blossom pollination. A cool start to bloom would delay a thinning app accordingly. All keys to the bees. The second app comes at 50 to 70% bloom. Heavy-setting varieties with significant straggler bloom (formed at the base of annual shoots but needing slightly more time to develop) will even want a third app at 90% bloom.

Another part of the storyline concerns rates. According to the Swiss, some varieties are more sensitive to bicarb and thus must use lower rates. The 10# per acre threshold should not burn leaves but ornery varieties may require a higher rate to get proper results. I noted earlier that Brian uses 12.5# per acre. This is more than double what the label states for anthracnose and mildew prevention. Thus the cost at a "thinning rate" looks something like $120 to $150 per application ... whereas thinning by hand might cost $2000 in labor per acre and never be as timely ... which is so key to delivering return bloom the next season. There's talk that bicarb dehydrates the scab spore as well so that's a plus in a rainy bloom spell.

And then I'd really like to know if bicarb sets back the beneficial microbe scene to the same extent as lime sulfur.

Lost Nation Orchard
Zone 4b in New Hampshire
Re: bicarbonate for thinning
January 17, 2020 08:05PM
A belated thanks to Francis B for the tip on using straight potassium bicarbonate! Milstop is very expensive when used at thinning rates. If you are certified organic, be sure to check with your certifier before any new materials...
Here is my update--I've been leery of increasing my rate (I used baking soda last year), and so have been using 6# per 100 gal which translates to 12# per acre since we put on about 200 gal/acre. Baking soda is cheap, a few dollars a pound similar to the KHCO3.
I try to put on 2 thinning sprays--one at ~30% bloom, then another 5-7 days later. It is difficult because we have over 30 varieties. Two sprays at that rate are not enough to fully thin the crop, but our hand thinning is much reduced. This year we saw little russet from the thinning sprays, but there is always some.

Hemlock Grove Farm
Zone 5 in New York
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