Plum black knot

General Fruit Growing
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I’m sure it’s been asked but…I use chlorothalonil beginning of the growing season on plums for black knot prevention. Got methly, toka, a pluot and pluerry.
What I’m confused about is what to use after shuck split?
Captan isn’t recommended until after all growth is done (July ish )?
Also T.Methyl isn’t recommended after fruit set.
So …after shuck split what are you guys using for the rest of the year?
Then I figured sulfur at the end of the year.
I’ve got the peaches down but the plums seem tricky to get this knot on point.
Any tips appreciated.

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After flowering I’m not aware of any spray for plum black knot.

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3

Topsin M WSB label says you can. I’ve been using it now for many years. To aide myself in the control of black knot, I do spray chlorothalonil (@ a reduced rate of about 25% with nothing else added) after fruit harvest. So far so good.

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4

I thought the main infection period is in spring. You may be wasting time and money with later sprays.

Chemical controls are only modestly affective at any rate.

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But fruit set happens in spring. So if I still have well over a month and a half from fruit set to end of spring then wouldn’t it be suggested to spray until end of growth (end of spring). That’s my mentality at least. I think I’ll go with T.Methyl and see what happens. Thanks for the reply.

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Alright. Thanks for that. I’m in NE Ohio , knot is bad here. So I’m trying to do what I can. Sounds like T.Methyl is the answer.

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Here’s some literature that doesn’t clear the confusion much. "Ascospore discharge
continues to occur for 2-3 weeks after bloom.
Infections take place during this time but may
continue for a longer time period if susceptible host
plant tissue is available. The germinating ascospores
have the ability to penetrate unwounded surfaces of
elongating, green shoots directly.

Thanks Prof, but how long after bloom is spray useful? I don’t even trust the lit, to be frank, In my nursery we remove all knots at least 3 times a season, but never get it under control. We are thorough.

http://plantclinic.cornell.edu/factsheets/blackknot.pdf

Let us know it you seem to have found a protocol that works- the consensus among commercial growers here seems to be, plant the trees and harvest them until black knot kills them then cut them down and start again.

We keep trees going in the orchards I manage by cutting out all knots at least once a year. It’s a never ending cycle that helps keep us busy. Not the funnest job though.

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Man that sucks. I’m going to try the T.Methyl and cross my fingers. I mean, it’s not going to harm anything I guess. Thanks for the article. I just found you guys and if I get clear results at least this year I’ll post some updates.

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9

After black knot started, I almost found it impossible to stop; so I cut down the trees.

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10

What ratio do you spray with Topsin per gallon of water? All I’m seeing is for acreage.

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11

I started out with about 12 plum varieties. When one developed black knot I removed the tree from my orchard. I have settled on 6 varieties that haven’t had any black knot for about 5 years now. With a high risk of the plums getting frosted each year I don’t want another serious issue like black knot.

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What varieties do you find work now and what do you spray?

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13

I don’t spray anything for black knot. Spring Satin, AU Rosa, AU Cherry, Splash, Guthrie, and Odom. This is 5 not 6 varieties.

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Wow. No spraying for bk… I’m impressed. Thanks for the info my man.

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15

Where are you located?

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I’m located about 30 miles south of Birmingham AL

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I use this guide.

ho83.pdf (145.2 KB)

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Hey thanks my man. This has become a hobby kind of out of nowhere. Bought a house with some property. I saw it as a blank canvas. And started planting slowly from grafted varieties and seed. Peach,plum pawpaw, pear and persimmon, couple apple. I had to cut down plums when I moved here due to black knot. So I want to do these right.

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19

I am now controlling by cutting out and then blowtorching. I have tried each of these separately and they work pretty well separately, but together they nail it. You need to cut until the deeper-green colored wood is all gone, only lighter green or ivory wood should be showing. Then blowtorch for maybe 30 seconds, get some smoke going. If it is girdling the whole limb this method won’t work, but for me only smaller limbs get girdled and those I completely remove.

In 22 years only one tree needed removal, it got completely covered in knots. I could have pruned it back but concluded the variety was too susceptible to keep around. Rosy Gage was the variety. For most of these years I controlled by either just cutting or just blowtorching. That kept me in plums but I had too many return infections (maybe 10-20% would come back) so I am now doing both.

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Hmmm…not sure what you mean by the blowtorch method. So remove the limb then cauterize?

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