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Frost protection before petal fall

Posted by Ian Graham 
Frost protection before petal fall
May 07, 2017 02:09PM
I've searched GOA forum for any gleanings on frost protection when we're given a weather forecast of frost. There are only three entries that mention frost so maybe we need a thread on its own.
We're getting a warning of light frost tonite, first time since thaw, apricots, plums, peaches, pears, serviceberry, cherries are in blossom and some apple varieties are at tight cluster.
TAG book pg 128 gives three suggestions: water spray, valerian extract spray and kelp spray. The options of orchard heat, air movement and bare moist ground are discussed.
Could growers speak to their success/not with the sprays, particularly for mild frost say 3 degF below freezing?

Old 99 Farm and permaculture site
Dundas ON 5b
Re: Frost protection before petal fall
May 07, 2017 05:03PM
Ian,

The critical temperature thresholds for fruit at petal fall and at fruit set are 25-28F. This is where you would expect to see between 90 and 10% bud/fruitlet kill, so a wide range of potential damage over a narrow range of temperatures. After the last few years, though, I suspect the temperature charts are too conservative because we have not seen the amount of damage you would expect based on the charts. So unless the temperatures dip too far below 28F or for too long or too quickly, you will only see mild damage, if any at all. Apples at tight cluster have critical temperature thresholds of 21-27F for the same amount of damage. My skepticism about the the accuracy of the charts holds here, too.

The theory behind the kelp sprays (or any other mineral spray) is that by getting the minerals into the cell cytoplasm you increase the % soluble solids (or brix) and reduce the freezing point of the cell constituents. Remember, only pure water freezes at 32F - all else has a lower freezing point based on the % soluble solids. The trick is beefing up the %SS in time for the frost or freeze event. You can't just start the night before, but rather need to "see it coming" and get a few sprays on. We've had these conversations before about how to measure brix in a meaningful way in the field to know the status of the trees. There are no quick and easy answers - everything is "it depends."

The Valerian sprays come out of the biodynamic literature and something I have personally taken quite a bit of interest in. In short, you need Valerian extract that you potentize by mixing in water prior to spraying. The first application needs to go on a few hours before the frost or freeze event occurs. The second application needs to be applied after the frost has lifted - but instead of just Valerian (BD507) you need to also mix with BD500. In biodynamic terms, this approach provides a warm, healing environment for exposed the plant tissue.

Both of the above approaches work, when properly applied, but only within the terms described at the top. You will not a save single fruitlet if the temperatures are 5, 7 10 degrees F below the minimum limit.

Orchard heat should be fairly obvious, but won't work unless there is some modicum of cloud cover. A clear, cold night only allows that heat to simply and freely radiant to the heavens. This is why smudge pots (or smoky fires) are still fairly useful, because they can create an artificial cloud cover within and just above the orchard canopy, trapping the heat and keeping the plant tissue at a safe temperature.

Lateral air movement across a flat surface can prevent the frost from settling, but isn't as effective as heat. Cold can kill just as easy as frost. But looking at it from another perspective, vertical air movement can move warm air from high altitudes (say a ridge top of a valley) into the lower reaches of the valley, causing a mixing of the two, raising the temperature of the air in and around the trees in the valley. Big orchard fans, helicopters, heaters, and various other heat/air generating contraptions have been used over the years, but only within a narrow range of temperatures.

So, how cold is it going to get where you are? If you are really only going to flirt with a few degrees below freezing, likely all the trees, and esp the apples, will be OK. You could try some sprays of this or that, but unless you have the products on hand and can get them applied in an appropriate time frame, you're better off saving your energy and letting nature take its course.

Hopefully this helps.

Mike Biltonen, Know Your Roots
Zone 5b in New York
Re: Frost protection before petal fall
May 07, 2017 05:17PM
well that helps a lot. Mike the diff in time zones helps this time!
I have the goodies for kelp and valerian root, but if you say kelp can't help if sprayed the nite of expected frost.
we're being told -1dC say -2dF so 30dF, not in the danger zone.
I do have a brix refractometer, would like to start using it with fruit. do you suggest any sources besides here for actually using the readings?

Ian
Old 99 Farm, Hamilton ON 5b
Re: Frost protection before petal fall
May 07, 2017 06:17PM
Ian,

The kelp is just better is applied several times leading up to a frost or freeze. It can still help if applied only once, just to a lessor extent.

As far as brix, the hard science related to frost/freeze protection is yet to be worked out. But science Schmience, one of the better sources for information on simple brix assessment of crop juices is the Bionutrient Food Association. Here is their document on brix content. You can click the back links to learn about what they do.

As well, there is sap analysis if you'd like a lab to do the analysis, but it takes time to get results. Crop Health Labs.

The best bet is to just keep your trees as healthy as possible all year long. This is where both in-house brix tests and sap analysis come in handy! Only use "rescue" treatments when you're really in between a rock and a hard place, or just want to see what the heck happens.

Mike Biltonen, Know Your Roots
Zone 5b in New York
Re: Frost protection before petal fall
May 12, 2017 01:04AM
thanks mike, the frost scare was overrated. I"m dealing with pear in full bloom, apple not past pink, plum and apricot, peach already into petal drop. A few trees each so it's not really possible to make one pass with my (new) 50 gal sprayer.
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