We had 3 extremely wet springs in a row, the first two led into wet summers. I’m hopeful that the extreme BK pressure is the result of these conditions and the more “normal” spring we are having this season will suppress this disgusting disease.
Meanwhile, I followed Scotts rec and ordered a small blow torch this morning. I’m getting too many return infections to removed galls. I used to spray the wounds with chlorothalonil immediately after surgery (butchery?) and never studied it in a way to clarify efficacy.
A very familiar story, but that seems to be how people are. They are attracted to a place by a beautiful garden , but then find it requires maintenance, so cut it all down. Seen it happen too many times.
This year the black knot is really really bad I have never seen so many black knots pop up on plum trees. I start to question the effectiveness of my dormant spray
I have heard commercial growers say that they just consider plums a short lived tree that you crop until the BK kills it- and they apply Captan frequently. Chlorothalonil is said to be the most affective fungicide against it in recs by Cornell and others. I don’t know what research they draw that conclusion from, but the caveat is always that nothing is adequate without contining gall removal in problem sites and seasons. along with the removal of nearby native cherry trees.
When I planted my first orchard here over a quarter a century ago I grew plum trees in an area with poor sun exposure, especially from the east, but for about 8 years never had a problem with black knot, I assume because of a sequence of very dry, hot springs.
It isn’t that the disease wasn’t well established, it was that conditions didn’t encourage it for a few years. Native cherries are numerous in the woods that lead up to my property.
In their recommendations to commercial growers the only fungicides Cornell recommend for black knot are chlorothalonil formulations or Topsin M. For brown rot they recommend a wide range of materials. In a discussion of black knot in their recs they state, “Bravo is the most effective fungicide for black knot control. Topsin M is only moderately affective.”
That is from the 2010 book. I don’t have time this morning to see if there is more current information, but the 2020 book may be free on-line through U. Mass.
I find that the best information from Cornell is directed to commercial growers. That is where I found out the myclo was not nearly as affective against brown rot as Indar.
This was just from today. From one mirabelle plum, Parfume de Septembre. There are more BK on the tree but I am tired of cutting them off and losing a bunch of plums. I will trim the rest off after harvesting my plums.
The size of these black knots and their location make it impossible to cut them off the knots without braking those branches.
Oh Tippy that picture makes me sick. Your Parfum de Sept. were my fav. Mirabelle! Look at all of the wasted mirabelles. That is horrible. I am so sorry. Ugh!
I thought I wanted to minimize spores spreading so I cut off infected areas when I saw them. After losing a couple lbs of plums this year, I have wised up and will do like you and @thecityman do, leave BK be and will remove those infected branches after harvest.
Last year, I removed several areas including two large branches that had numerous infection. If the trend continues, I may not have much left of the tree!!
@mrsg47 your area is probably much drier. That will be to your benefits.
From what I have read, the spores are released in spring. I don’t think it will continue release the spores during summer~ winter, I could be wrong though, but this is my understanding.
It is much drier. When it rains hard here, there is sand in the mixture so my outdoor white dining table is beige after any rain storm. It comes up from Africa. We need rain right now. We’ve had hints but little to no humidity. Just plain hot. 92 today.
They will not stop growing during the summer. They will spread and get larger. Just before i left I discovered serious black not especially on my Italian Prune Plum. I left it go and enjoyed the plums.
This university guideline state this, although it seems if it was true we wouldn’t all be having so much trouble controlling this disease. “Generally, the knots produce no spores until the second spring after they become visible.”
It also says the spores continue to be released and infect new wood until terminal growth stops, which seems not to happen until fall if you control leaf hoppers in E. Plums.
Trying to understand how severe the burning of the black knot on the tree should be.
Do you burn beyond the obvious fungus?
Do you scrape off the burnt fungus?
