Fireblight pruning

[FBerkel]

I heard from the Man himself (Shigo), that sterilizing tools to avoid spreading fireblight seems to be an old arborist's tale: he said his grad students could not spead fireblight from 100% culture into uninfected trees through pruning wounds. This was 15 years ago. Every article I've read since begins from the assumption that it can be spread, but I've yet to see one that footnotes any study showing that this is true. My own experience is that pruning blighted trees without sterilizing, only during the dormant season, is safe. I do dozens every Winter. It makes sense, sinced the bacteria are holed up inside their cankers in the winter for a reason.

(Shigo also said it doesn't hurt to sterilize with 10% bleach
and suggested that it therefor might not be a bad idea)

 

[Stumper]

FB, Was Dr.Shigo's study on dormant pruning? That would not be so surprising but I would expect some transmission during the growing season. As the Dr. said sterilizing does't hurt.

 

[FBerkel]

His study was in season, if memory serves me. I f anyone prunes blight in season (the only reason to do so would be a last ditch attempt to save a rapidly dying tree), they should definitely sterilize, IMO.

 

[John Paul Sanborn]

Let's use proper verbage here. Sterilize is to kill all colonies of micobes, which would require an autoclave.

Sanatize means you get enough of them to make the chance of infectioon minmal.

 

[Nickrosis]

I was just as his workshop yesterday, but I think I have enough questions already to call or fax him. Let you know about this... The workshop was great - at the Sugar Shack near Durham, New Hampshire.

Nickrosis

 

[FBerkel]

Nick,

Would appreciate it if you'd post any response you get out of him on the subject.

 

[Nickrosis]

I have faxed him the question and will let you know when I hear back from him.

Nickrosis

 

[Nickrosis]

Shigo's Response

Today, I received a response from Dr. Shigo. I will quote it in its entirety.

"Fire Blight - Sterilization - When I see some data I will believe it! Until then, I doubt it will help. - The disease has two parts: flower infection that spreads to new growth only, and crotch infection after the bacteria build up on the new growth. Why would you prune new growth? -

"My thoughts only."

Alex Shigo
_______________________
I hope this helps.

Nickrosis

 

[Nickrosis]

This would help too.... Here is what I sent to him originally.

"My other question is simpler, and I would be grateful if you could clear this up. Here is what was written on the online discussion board as well:
'heard from …Shigo… that sterilizing tools to avoid spreading fireblight seems to be an old arborist's tale: he said his grad students could not spead [sic] fireblight from 100% culture into uninfected trees through pruning wounds. This was 15 years ago. Every article I've read since begins from the assumption that it can be spread, but I've yet to see one that footnotes any study showing that this is true. My own experience is that pruning blighted trees without sterilizing, only during the dormant season, is safe. I do dozens every Winter. It makes sense, sinced [sic] the bacteria are holed up inside their cankers in the winter for a reason.

(Shigo also said it doesn't hurt to sterilize with 10% bleach and suggested that it therefor [sic] might not be a bad idea)'

Someone asked if the study was done during the dormant season.

'His study was in season, if memory serves me. If anyone prunes blight in season (the only reason to do so would be a last ditch attempt to save a rapidly dying tree), they should definitely sterilize, IMO [in my opinion].

--Fred Berkelhammer,
President, Berkelhammer Tree Experts, Inc.'

He has this tree company out of Boulder County, Colorado. If you could clarify this when you have the time, I would certainly appreciate it."
____________________________________________________
An answer needs a question, and there it is.

Nickrosis

 

[Stumper]

In answer to Dr. Shigo's question....."why would you prune new growth?" Because some nincompoop 'topped' the tree reducing it to stubs of scaffold branches. The resulting mess may leave you with nothing to prune but new growth. That said it would seem that under normal conditions there is little need to sterilize tools.-I'll probably continue however until a study proves that it is a waste of time. My subjective impression is that it does reduce the recurrence of fireblight in Apples and pears.

 

[FBerkel]

Thanks, Nick. He seems to be questioning the whole premise for my original question, that one should prune out fireblight in the first place? Wow!

 

[John Paul Sanborn]

I asked Meesh-el Quinn, a phc eggs-pert in Missery about her thoughts on it.

___
don't think it would be so much of a concern - fireblight bacteria can hang out in
cankers and be relatively dormant until weather conditions are right, and then they take
off. i think it would be a good idea not to prune an infected tree in wet weather and
maybe not even in warm weather with high humidity. literature says 65-85 F is
optimum temp for fire blight to be active. but just because we don't make pruning
wounds doesn't mean the bacteria that are present won't spread. in my opinion, if it's
dry and cool or dry and hot the risk of spread is very minimal, wound or no wound.
certainly we're not going to avoid fireblight by avoiding pruning, as it's going to take off
when the conditions are right as long as the bacterium is present. i guess the question
is whether avoiding pruning except when dormant would reduce the risk of infection,
and my opinion is that it wouldn't be significant enough to be concerned. major
avenues of new infections are buds and new shoots, so avoiding wounding is not likely
to significantly reduce infection. quite obviously when i look around the campus at all
the fireblight we have in the last two years, it's not by any stretch of the imagination
worse on trees that were pruned during growing season. three to six years ago (since
i've been working here) it was essentially non-existent. weather conditions.

that's my opinion - it is not shared by all...some literature will say to avoid pruning
during active growing season. and i suppose one more wound is one more place to
become infected...but since it can infect through pores and blossoms - what's one or
two pruning wounds? i think that the most susceptible parts of the tree are the
succulent new growth anyway - probably not where the pruning cuts are made.

 

[FBerkel]

I don't know...maybe I'm too hooked into the orthodoxy on this one, but seems like a pruning wound is a much bigger target than a pore: greater chance of bacteria washing over it.

Soes seem like many of the past assumptions go flying out the window, e.g. don't cut American Elm in the growing season....

 

[John Paul Sanborn]

That one went out the window bout 2 years ago. WDNR no longer recomends using months ending with an "r" in elm planning. Any time is good.

The tought now is that the beetle is attracted to the scent of the expanding growth. There is more of that then any amount of cuts we can make.

They feed on twig unions, the old wisdom was that the scent of feeding attracted more beetles, but these wounds are so small.

Mini-apple-us looked at losses of trees prunned in different seasons. it was an unscientific study, in that the samples were small and over a short time period and there were no parameters during the pruning. They just analized the numbers and found that there was actualy a slightly higher mortality in winter pruned trees.

Maybe Tom can get someone more familiar with the study to comment?