It varies with the species of tree, and also with what the purpose of the pruning is.

You prune differently for shaping versus fruit production enhancement. And the age/size of the tree also matters.

Scott

When wood attacking fungus is a problem, such as with canker, the trick isn't fungicide but for the tree to be actively growing. Peaches heal faster when pruned in spring, apparently cherries suffer less when pruned in August.

I prune fruit trees on about 7 months of the year.

Well it's the cherries, MSU says if you prune them, you should put copper on them. And yes August is better but sometimes a cherry tree say on gisela, it may have too many terminal buds and not enough leaf to support the buds. They should be trimmed back in the spring or late winter. You may be able to do this in August which is the very best time for cherries.
Also copper can be used for peach leaf curl at this time. I figure you're out there pruning might as well spray them too. MSU suggests once after leaf fall, and once before bud break for peaches. In the west they suggest three sprays.
I actually will be using another product for PLC this year, but copper is a must for my cherries when pruning.
MSU has some radical approaches. For example on cherries they suggest if canker is a problem to leave prunning stubs. I guess the idea is to keep the canker away from the trunk if it becomes infected. Not sure really?
One link about the copper is given, but they have multiple documents on cherry pruning.
It won't hurt to spray your trees at this time. Yes, they will need more sprays. Your approach is minimal, mine is not.
I trust MSU, so I'm going to do what they say.
I figure if you disagree you would respond and sleone can decide how to proceed. Some universities give bad advice, but I don't think it is the case here.

Pruning after terminal bud set in mid summer does not stimulate new growth, in my experience, and espaliers have traditionally been pruned at this time for centuries. I prune apples every working day from July well into Sept so I have less to do in winter when I'm pruning every single weekday as well.

I've never really suffered consequences of pruning at a "wrong time" although when I started in all this I followed the literature and was very cautious. It was the sanguine attitude of commercial growers who would prune most any time that gave me the confidence to follow the old saying, "best time to prune is when the pruners are sharp".

That must be nice I have had it twice already. And I only have 3 trees.
One tree had to be removed it was bad, why they suggest stumping here. I prefer to follow MSU's advice. You have no experience in my area. They do. If you read the bulletin they not only tell you to spray after pruning, they tell you to spray BEFORE too! And I do. This has worked really well.
But I appreciate your advice, it is interesting, but I prefer to error on the side of caution. If others want to ignore canker infection possibility, that is their prerogative. As general advice, I think it is rather poor advice. My trees are on Russell Island, and it is super moist there. Potato chips last one day there before they have no crunch. I have been having a hard time growing anything there. But slowly I have been finding ways. And I do get a decent cherry crop despite the worst possible conditions. I have learned a lot. I have certainly learned canker is alive and well in my area.

In this case you initially recommended your approach without specifying that it was based on an issue with a single species. I think this clarification is helpful.

If you rely entirely on the advice of people whose information is acquired in the arena of commercial fruit production you may never learn the difference of what is required to grow a small stand of fruit trees compared to growing in multiple acres of monoculture.

I did not learn practical home orchard care by relying on Cornell. Their experts can offer advice when a specific issue occurs but they aren't very helpful if you want to pursue a low spray regimen to produce sound but not necessarily pristine fruit. You sometimes have to risk your crop or even your trees to learn what you need on any given site.

If I erred on the side of caution as a general rule I would wind up spraying all the orchards I manage twice as often as necessary. If I followed Cornell's advice on when to prune, I'd be able to manage a fraction of the orchards that I do now and I'd have to make my living doing something else.

That is really good advice, and I do now too, but when I first started my cherries, I was new to fruit trees. I didn't know better and a couple trees got infected with canker.
One responded well, the other the infection went to the main trunk, and I lopped it off, the tree leafed out well, but then suddenly died and had to be removed.
I have 2 places 35 miles apart and the conditions could not be more different. Here in the city away from the water, and the old growth forest, it's dry. Easier to manage my trees here. Still last year was a wet spring and I saw a few fungal infections on strawberries, cucumbers, and on a magnolia tree. I removed the tree. I have found some products I will be trying this year to eliminate any infections. Including anti-fungal drench before transplanting, and use of beneficial fungi and bacteria, plus trace minerals to establish vegetables as early as possible. They now have anti-fungal bacterial products, pretty cool! Not for trees, well not sure? Actinovate is the product. I will use more traditional fungicides too. At my cottage it is so wet, all precautions one can do make sense there. I always will try new products too. When using fungi and bacteria it is best to buy directly from the manufacturer as some of the products have a short shelf life and you could be putting on dead spores. Some are excellent! We know about mycorrhizae fungi, one product contains every species you would need for vegetables. It has 9 Endomycorrhizal fungi, 7 Ectomycorrhizal fungi, 2 Trichoderma fungi and 19 beneficial bacteria.
I really like this product when growing stuff in containers as you are putting plants in pretty much a sterile medium. This is a jump start. Works great for containerized tomatoes, cucumbers, etc. Sorry off subject some, just related to using biologicals for fungal defense.
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I'm not familiar with it? But conditions are wet here in late winter, and MSU a local University advocates late summer pruning for cherries to decrease chance of bacterial or fungal infections. MSU suggests to prune in august. Cherries are our states life blood. it is a major crop here, we grow the most tart cherries of any state, or country for that matter. It is super important here. Although I happen to be talking about sweet cherries. What i like about MSU is they have extensive information not only for the commercial market, but for home growers too. They have developed many cultivars for both markets. MSU has developed more blueberry plants than anything, but recently 2 tart cherry cultivars were released. I think the cultivars are for both markets, you can purchase them at Grandpa's nursery which is located in Michigan. They are very much like Balaton.

Here's some info on what we are facing here from MSU. In 2012 many orchards got hit, and so did I. A major portion of our commerical fruit trees were taken out in 2012.

Because canker isn't generally an issue on pie cherries, I prefer to prune them in the dormant season. It's the only fruit tree type I don't summer prune. The reason, pie cherries are prone to get leaf spot here. They want to defoliate in late summer anyway (which weakens the tree). I assume cutting away summer foliage (via pruning) would add to the problem.

Everything else I try to prune when I think it needs it (i.e. prune in summer when the fruit needs more sun, prune in winter to thin wood).

learning

school

We have had severe infections here in pie cherries too, it can be a problem. I would not rule out canker in your trees, leaf spot, defoliation can be symptoms.

I was really excited about the Romance cherries and planned to put in a couple rows, but SWD checked me. I'm afraid of what they would do to the fruit in a larger planting.

Yes, I'm worried about that too. I just ate some of my raspberries with oatmeal, frozen from the fall harvest, and man they were so good, with oatmeal and nuts. The taste was out of this world compared to store bought! Man, I'm going to miss them if SWD hits me!
I was thinking about nut trees if SWD becomes a problem, which again going on a tangent, I found a 2nd nursery with shag bark hickories for sale. I'll post info if still looking.
Have you seen the new almond cultivars that are true soft shelled almonds? Not peach-almond hybrids. I was thinking of growing some of them. Rated to zone 5. One Green World has them! That's an awesome nursery btw!

By coincidence only, the University of Oregon seems to agree with my recollection. Not fans of copper for this affliction- that's for sure. Better make sure that's the right approach.

There is very detailed info here.

Oops! I have to take that back, they have worked and made a number of videos with MSU about MI cherry trees.
Looks like these guys have worked together to study how to use Gisela rootstocks, A collaborative project of: Dr. Gregory Lang, Michigan State University; Lynn Long, Oregon State University; Win Cowgill, Rutgers University; Jon Clements, UMass Amherst; and Gisela® Inc

Do you have something more recent than this?

However, upon further reading, I've found that your information is correct and copper spray is widely recommended after pruning even though it isn't very affective- but enough so to be worth doing according to current Cornell and other guidelines.

I stand corrected and thank you for bringing this to my attention.

After reading all this material about cherry canker I am somewhat surprised that my careless timing of pruning has never led to any outbreaks of this infection over the last 25 years.

Cherries are a minority species in orchards I manage and I am very busy doing non-pruning work in the first couple weeks after trees come out of dormancy. It would be expensive to come back to prune only cherries and peaches at many of the smaller orchards I manage.

I recently started managing cherries with summer pruning anyway- but only to better manage fruiting wood. I will now pay more attention to weather forecasts before performing this kind of pruning. I will wait until I actually see some cherry canker somewhere before I start spraying after pruning. I have to keep customer expenses down.

If you hadn't posted about it I wouldn't think about cherry canker much at all.

Thanks again.

Some people are just good at what they do.
I myself as really a beginner here, have had terrible luck with cherries. Last year I managed to secure a Cupid and Romeo plant from the Romance series. Not sold in the USA. Both are dead. No chance of replacing them.
I'm ready to throw in the towel! I do have a couple of sweet cherry trees that are doing OK in a bad environment.I lost one, another I'm battling canker on, it is OK for now. The third never got it. I though do not plan on replacing them, should something happen. It's just too hard to grow them at my cottage. I will grow cherries in the city from now on. Others on the island have trees, but they are in better locations. I'm in the middle of the woods, besides the moisture, the air flow is low there. I have found that the Cornus Mas Dogwood grows well there, bamboo, variegated plants, and some wild brambles. I'm going to try highbush cranberries, and swamp currants. I've often said I have ideal conditions in the city, but really anything is ideal after dealing with the environment on a small island in the middle of a massive river.

I assume you noticed that growing cherries on berms is highly recommended and seems to make as much difference as anything else you can do for most all that ails cherries.