# Fighting black knot



## Full Skip (Mar 22, 2006)

I was delighted when we moved into our new home that there were three American Plum trees in the back of the yard, but over the summer, I noticed that two of them were infected with black knot fungus. Neither have anything on the main trunk, but the branch tips are covered and I'm in the process of cutting everything back now.

I have moved the smallest of the three and also the least infected and I'm pretty confident that I can control the fungus on that one.

what sort of prognosis am I looking at as far as the other two? One is about 18' and the other is about 10'. If I am to remove all of the knots that are currently on the branches, I'd need to trim nearly every single branch back considerably. I don't have any experience with fighting this stuff.

Is that sort of pruning even surviveable?

One other problem is that over the years, American Plum trees have formed a thicket all the way down a 20' oil pipeline ROW which runs through my yard, between two others and on down through the neighborhood. Some of these trees are infected as well. Surprisingly, some of the trees are completely healthy.

My main question is: am I wasting my time trying to control this with pruning and fungicide considering the other infected trees in the area?


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## Kate Butler (Mar 22, 2006)

*black knot*

"Is that sort of pruning even surviveable?"

Yes, if you do it over time (incrementally over 2 or 3 seasons) and not all at once.

"One other problem is that over the years, American Plum trees have formed a thicket all the way down a 20' oil pipeline ROW which runs through my yard, between two others and on down through the neighborhood. Some of these trees are infected as well. Surprisingly, some of the trees are completely healthy.

My main question is: am I wasting my time trying to control this with pruning and fungicide considering the other infected trees in the area?"

Possibly - but unless the infestation along the ROW is severe, the trees will survive. Black knot is unattractive, but surviveable over a long period of time. Treatment should improve your odds.


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## treeseer (Mar 23, 2006)

I agree with Kate, but it sounds like you should be removing entire plants out of the ROW, worst first.


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## Kate Butler (Mar 23, 2006)

*ROW pruning*



treeseer said:


> I agree with Kate, but it sounds like you should be removing entire plants out of the ROW, worst first.



Y'know, I thought about that, but some of the neighbors might object. Or, depending on local regs, you might need some sort of permission to do that. Definitely worth inquiring about.


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## Full Skip (Mar 23, 2006)

Technically I'd need permission from the gas company to do anything on the ROW. I've tried calling them and I get a computer. That's always annoying. Every so often a company truck will be in the neighborhood. I think that trying to talk to sombody on a crew would be my best bet.

As far as leaving some of the infected branches.

How dangerous are these infected branches to new growth as far as spreading spores?

Should I prune back what I can for the season and just hit everything really good with a fungicide prior to budbreak? Is that going to be enough to ensure some new growth? From what I understand, it is only the new growth that is succeptible.


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## Kneejerk Bombas (Mar 23, 2006)

Here in SE WI, black knot is the major identifying charictaristic of prunus.
I like black knot, it's neat looking. It's like flower galls on ash, that's cool too.
Dog Vomit Fungus is another interesting beauty in nature.
If you have the right attitude, it'll save a lot of work, cutting all those beautiful fruiting bodies out. And you'll save money and the environment too, sparying harsh chemicals that really don't work. 
It's all in your perception of things. In nature things are not always in neat rows or with straight lines, although those things make some people happy.
Removing whole trees because of a bark inconsistancey? Wow, that's radical! I thought it was silly to prune the knots out...


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## Full Skip (Mar 23, 2006)

My attitude is that I'd like to have a bunch of prunes to make wine with. You get less prunes when the branches die and fall off.

I have the right attitude. Trust me.


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## treeseer (Mar 23, 2006)

Mike down here black knot can and does kill branches and trees. I don't know where verona is so I can't advise the poster more than that.


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## Full Skip (Mar 23, 2006)

I thought that I put Verona, PA. I guess not. Anyway, I'm in Pennsylvania, not Italy.


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## treeseer (Mar 23, 2006)

Full Skip said:


> I thought that I put Verona, PA. I guess not. Anyway, I'm in Pennsylvania, not Italy.



And I'll bet you are one of at least Two Gentlemen from Verona (PA)  a la Willie the Shake

re cutting on ROW, I'd be surprised if anyone noticed or cared, but ask away.

Mike M is in WI, where black cherryPrunus serotina is a valued element of the forest canopy. My forestry prof at UW did his dissertation on it. Here in NC it is rare to see a big one due to the gall. Since you are closer to WI in climate, it may not be as huge a deal, but it is not likely just an ornamental nuisance as he suggests, especially on a fruit tree.


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## Urban Forester (Mar 23, 2006)

Black knot is caused by the fungus, Dibotryon morbosum (another name for the fungus is Apiosporina morbosa). The fungus overwinters in knots on twigs and branches or in the infected wood immediately surrounding them. In the spring, the fungus produces spores (ascospores) in sacs (asci) contained within tiny fruiting bodies on the surface of the knots. These ascospores are ejected into the air during rainy periods and are blown for moderate distances by wind currents. Only succulent green twigs of the current season's growth are susceptible to infection. Ascospores that land on them may germinate and cause infection if the twigs remain wet for a sufficient length of time. Normal growth is disrupted in the infected regions, and a knot is formed as the fungus causes the plant to produce tumorlike growths. Knots may become visible by the late summer of the year of infection but often are not noticed until the following spring, when they begin to enlarge rapidly. New ascospores capable of spreading the disease may be formed in the young knots the year following infection but often are not formed until the second spring. The fungus continues to grow in infected wood during the spring and fall months, causing the knots to elongate several inches each year and eventually girdle affected twigs and branches. Ascospores are potentially available from the time of bud break until terminal shoot growth stops, but the greatest number appear to be released during the period between white bud and shuck split. Although the precise environmental conditions required for infection are uncertain, only a few hours of rain apparently are required at temperatures above 55 degrees F (13 degrees C), whereas much longer rainy periods are required to produce infection at temperatures below this threshold. Fungicides can offer significant protection against black knot, but are unlikely to be effective if pruning and sanitation are ignored. The timing of fungicide sprays should be adjusted to account for inoculum levels and weather conditions. Where inoculum is high because of an established black knot problem or a neighboring abandoned orchard, protection may be needed from bud break until early summer. Where inoculum has been maintained at low to moderate levels, sprays are most likely to be useful from white bud through shuck split (the period of maximum availability of ascospores). Fungicides are most necessary and will provide the greatest benefit if applied before rainy periods, particularly when temperatures are greater than 55 degrees F (13 degrees C). In evaluating control programs, remember that knots often do not become apparent until the year following infection (from OSU) A product containing Thiophanate-Methyl (Clearys 3336 or equivilent) is recommended.


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## treeseer (Mar 23, 2006)

OK I follow all that except "Only succulent green twigs of the current season's growth are susceptible to infection.", because i see big honkin galls on 12"+ stems, and I don't think they've been there since the stems were green twigs. But maybe they were.


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## antigrassguy (Mar 24, 2006)

Fullskip, I understand your desire to make homemade wine. My dad makes a kick butt oak leaf wine. But youve got black knot on trees in lawn and a gas ROW that is thick with plums. "some are unaffected" Have you thought of trying to propagate plums that are not effected? Could be fun and profitable. I would harvest plums out of ROW, how mad could they get for this?, and make wine. Then I would encourage the black knot to GROW, buy a wood lathe and then turn some awesome gobblets out of knots for serving your necture. . Have fun and good luck.


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## Kneejerk Bombas (Mar 24, 2006)

I have a problem with satitation, to some degree. 
If you are dealing with an uncommon plant, with an unusual disease, then by all means, sanatize the area. But with black knot in my area, it's like apple scab on crabapples, you can do your best to sanitize, but that won't stop the spores that float in from 10 miles away. You'll still have black knot on your Prunus and scab on your apples.
These are just examples from my geographic area, but you should get my point.


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## antigrassguy (Mar 24, 2006)

Good call, treeco. EOM


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## Kneejerk Bombas (Mar 24, 2006)

Full Skip said:


> My attitude is that I'd like to have a bunch of prunes to make wine with. You get less prunes when the branches die and fall off.
> 
> I have the right attitude. Trust me.



I have noticed that dead branches don't seem to produce as much fruit. 

Are plums like apples in that they produce bigger fruit when they are pruned hard? If so, maybe the black knot is not as bad as you think.

Your comments do lead me to believe in the case of fruit production, sanitation and spraying may be the way to go.


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## Kneejerk Bombas (Mar 24, 2006)

antigrassguy said:


> Good call, treeco. EOM


Another thing is picking asparagus along the road side, where they often spray broad-leaf weed killer about harvest time.


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## antigrassguy (Mar 24, 2006)

Mike, thats overrated. Ive eaten lots o' aspergrass and I'm fi.. fi.. fi.. fine. IMO.  But I dont have it in writing.


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## Kneejerk Bombas (Mar 24, 2006)

The Dioxin in the weed killer shouldn't be bad for you, they government said it didn't have any effect on the guys they dumped it on in Vietnam anyway. It's the taste that bothers me.


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