Oh! Good approach.
I had a damson for a couple years, the thing would be more black knot than wood every year, despite me cutting it off as soon as I saw any black knot appearing at all (which amounted to removing probably 1/4 of the treeās limbs annually). Thereās a wild cherry grove close to me full of black knot, and some old damsons that are also mostly black knot on a neighbourās property. Trust me, apples are far more worth my time here haha. Thank you for the tip though nonetheless.
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Have you tried any of these?
Chlorothalonil
Copper Hydroxide
Copper Octanoate
Copper Sulphate
Propiconazole
Thiophanate-methyl
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Do you ever get problems with lack of chill hours?
I recently planted Green Gage and Bavay (also called in Spain Reina Claudia Tolosa) in my farm in Southern Spain, and I generally donāt get much chill. The climate is sort of similar to many areas of costal California and the Valley.
I planted them anyway, because the Green Gage and Bavay are one of my favourite fruit, but Iām intetested to know of people in a similar situation to my own.
In Spain itās a classic of late summer. They are the only commonly sold euro plums, now that the asian plum has taken over most comercial orchards.
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My Green gage from the house in the Bay Area, my daughter texted me this recently, pictures of this tree is 10 years ago. I think I bought from Raintree nursery, maybe itās a Bavay. Itās very tasty, very sweet.
I never fertilized or did anything to it.
Itās incredibly productive.
Close in shot of one side of the tree
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That is very encouraging, that tree looks fantastic! And knowing it was a great producer gives me further hope.
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I looked at my zone in the Bay Area, itās between 9b to 10a.
Scott, this is the first time Iād heard of anyone suggesting to blowtorch a living tree you intend to keep, but Iām intrigued by the method and will add it to the wheelhouse. Thanks for sharing.
I bought a blow torch at Scotts recommendation and couldnāt really figure out how to use it. I tried it on several trees but didnāt notice particularly positive results. Itās pretty hard to tell how hot youāve gotten the tissue. Your eyes tell you nothing. Rather than a blow torch, I cut it out and spray wounds with chlorothalonil. It may reduce the chance of return infections to a wound site. Seems to.
Iāve spent a lot of money paying my helper to cut it out in my nursery the last few years since weāve had a string of wet springs. It amuses me if someone says they know exactly how black-knot will behave as a general rule because I see so much unpredictable fluctuation between sites not related to sun exposure or varieties.
Can anyone find any research on the subject of controlling or suppressing black knot with a blow torch?
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As far as I know it is my own idea and my own informal research in the last five or so years says it works well.
One downside I am finding as I prune now is the torched ones donāt look very different from live ones. I need to chip them with my pruners sometimes to make sure they are dead ones.
Before the blowtorch I was pruning them out and it was working fine but maybe one out of three times it would not all get cut and would come back. With torching I am so far batting 1000.
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I was hoping someone else would pipe up who followed your suggestionā¦ you have been suggesting this approach for some time. Return infections are not the largest problem to meā¦ unless they are leading to more new infections.
What Iāve found works exceptionally well is dry stretches during the growing season 
. Seriously, spring was wet last yearā¦ again, but things did dry out at times during summer and black-knot pressure was much less.
Could you tell me a little bit more about the location? Where in Bay Area? Also, do you have any pictures of the fruit? I know of a few places in Bay Area where Bavay Green Gage was planted and so far not very productive (close to zero). However, all of them were planted in the last 4-5 years and I hear these trees take longer to produce. I planted one in my home in San Jose and I didnāt see any fruits for 3 years as well. I pulled it out this year in my quest to replace all citation rootstocks. I was wondering if we just donāt get enough chill or the tree might take longer to produce.
Iāll pm you the location. But itās north of San Jose.
I donāt have any picture of this fruit, Iām trying to find that close up picture but itās lost, itās very prolific and big size like my Shiro.
Iāve torched black knot in the past and it was effective in stopping spread of that knot. 3 years in and the branch I attempted to sterilize with fire has proven safe from further spread of the infection.
Unfortunately I have an apartment bld nearby with a prunus padilla (mayday tree) with limbs that seem both covered and surviving with the infection.
Scott
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This blowtorch technique is intriguing Scott. Do you have to kill the bark or just singe it on the exterior?
I do not have blackknot but I am adding a number of plum varieties by grafting so someday I may need to know how long you apply the heat?
Thanks for answering any particulars you remember
Dennis
Kent, wa
I would say try to get the sap boilingā¦ that will āsterilizeā any virus. The knot can be fairly deep in the wood so you need it all boiling so you need several seconds of torching, maybe five seconds on an average sized knot. If they start giving off smoke that means you can do a little less time on the next knot.
If the limb is not too wide you need to be careful to only heat one side, it if is killed all the way around it will girdle. I never girdled a limb though.
Note this technique I also use on bacterial canker. It is more useful on that since canker is more severe for me (on cherries and plums), I have saved several trees that probably would have died otherwise.
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Thank you for this Scott. If the wood is pencil size how many seconds of torching would you recommend?
Zeroā¦ it wonāt work on small wood. I only use it on wood at least an inch in diameter. Anything on smaller wood I just cut off completely. Knots tend to be all the way around the limb in such cases anyway.
Cornell has and so have I, if less scientifically. The benefit seems to be modest and certainly hasnāt cleared up problem sites where Iāve tried a couple sprays during peak infection time.
Every university based guide Iāve read suggests that no fungicide is very effective in controlling this disease and given how time consuming cutting it out of trees and how damaging it can be, if there was a chemical cure I suspect commercial growers would be all over it. One commercial grower here once told me that most plum growers simply let black knot run its course until trees fail to produce enough fruit to be profitable, than remove them, burn them and replant.
Commercial guidelines also recommend eliminating all native cherries anywhere near a plum orchard. Maybe someone should write Cornell about Scotts method. Iād like to see the results of a controlled study even though I trust Scotts anecdotal observations as much as I can trust anybody on that basis.
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