Mark, once a tree has fireblight, the bacteria is spread through the entire tree, even if the wood is healthy. At that point, all you can do is just cut out any branch that shows signs of infection. The aim at removing the branch isn't to rid the tree of fireblight, but to prevent the infection from spreading to other trees.

I've read the literature on this and didn't believe it when I first read the fact that fireblight bacteria will travel all the way from the point of infection (flowers) down to the roots. However, over the last couple of years, I've had numerous fireblight infections that I got to observe. On an apple tree, fireblight entered through the blossoms and fast growing MM-111 rootstock sucker tips started to show infection. On a pear tree, a branch got infected, but the variety was fairly resistant. However, on the same tree that was grafted with other varieties, grafts of obviously highly susceptible varieties started to get infected starting from the graft point upwards. That was proof beyond any doubt to me that the fireblight bacteria had traveled all the way through the entire tree.

Fireblight thrives on fast growing shoots, but can't really grow much in areas of the tree where the level of carbohydrates is high. So the best thing to do is to cut the infection out down to last year's wood. If the infection goes beyond that, then keep cutting to the next big branch.

Oh, and cleaning nippers is a waste of time since the bacteria is throughout the tree.

My observations have been somewhat different than Axels. While there may be some bacteria throughout the tree, in most cases the symptomatic infection stays highly local. By highly local I mean only a couple inches below the visible signs. Axel, the rootstock suckers are some of the most susceptible shoots for fireblight so I expect you were seeing an independent infection of them. For the other grafts that got infected, I agree that could be from a small amount of bacteria traveling through the plant to highly sensitive varieties.

I prune shoot infections only 3-4 inches below; blossom infections on a spur off a scaffold I just pull off the blossom. Bigger limb infections I will do a foot on if it won't take out other branches; I will do less to save another limb. The bacteria start traveling down into the tree after the infection; big infections get a bigger pool of bacteria going down. When you are pruning you are pruning at a point where "most" of the bacteria didn't get across the line of the cut, so there will not be enough to damage the rest of the tree. That line is fuzzy so its a judgement call. If you are too high its not the end of the world, in a few days you will see the wood at the cut is looking necrotic so just take more off.

Scott

Thank you both for your very helpful thoughts.

Is the darkened cambium sign indicative or just coincidental? And does the copper help prevent against new infection?

Thanks again,

Mark

I'm seeing a lot of FB shoot blight this year, even though it's been quite dry. Sure it's been hot but not especially humid so I wonder if Scott or Axel or anyone else can explain why so much more persistance of this damage this year.

Usually I'll only see it at a site or 2 and when I remove the dead shoots it's the end of it, often indefinately, but this year I have removed shoots as much as 3 times from sites with zero rainfall between strikes.

I would say that there are strikes at 4 times as many sites as I've ever seen and not a single strike on pears. So far the damage is primarily cosmetic and does seem to be subsiding, as you'd expect as dry conditions are morphing into serious drought(by east coast standards).

I also get that. My current theory for my orchard is my quince was harboring a lot of blight which was re-infecting everything over and over. I wasn't paying enough attention to it but this year I have been and it had a lot of blighted fruits, shoots, stems, everything. Since I got on top of the quince I have not had a single infection elsewhere. More generally I would say its that there are blighted limbs/fruits which are nearby but not getting taken out and they right weather conditions wake them up. They may be on your property, or on the neighbors. It sounds like you are getting infections during periods of no rain at all? I may have seen a few of those but its generally the rain that brings on the infections - even a light rain in a dry period will bring them on. Maybe morning dew can also be a time when the disease can propagate without rain? You may be seeing more of it due to the higher temps - 85F is ideal propagation temperature for FB.

One thing I have done in the past to try to limit later blight is to paint over anything on any limb that looked like it may be an old FB strike on a scaffold.

Speaking of rain, its finally raining here now for the first time in several weeks. Ahhhh. The grass was looking totally burned out and I was noticing bushes and small trees all over town getting sad or dying.

Scott

My understanding of the disease process is that while the bacteria do travel internally within the tree, a peripheral strike does not imply that the whole tree is necessarily infected or that the tree cannot be cured of the disease. The goal during the bulk of the growing season is to reduce the bacterial load by pruning, which not only lessens the likelihood of spread to other trees but reduces the innoculum in the affected tree with the aim of preventing further spread within the tree and subsequently the development of overwintering cankers. Now trees that are hit hard, especially low on the central leader or on the rootstock are best removed. Those with peripheral strikes, I believe, should be managed aggressively with the intent of eventually eliminating the bacteria from the tree by immediately pruning at least a foot (and probably more) below any visible signs of the disease in the leaves, bark or cambium. This is to be followed by further and even more aggressive pruning during the dormant season. Less aggressive approaches I would think leave bacteria that could multiply to very large numbers and be more likely to spread further into the tree.

Thanks Scott. By the way, I think I was the one who suggested to you that quince is the typhoid Mary of FB.

Yes, I think your comments got me paying a lot more attention to my quince - I knew it was bad but I didn't realize how bad until I started looking.

Scott