Frost damage or something else?

Question: I just noticed this evening that my three Snowdrift Crabapple trees have some type of disease or damage.  All of my trees leafed out and bloomed early this year due to the early warm temperatures, then we had back-to-back nights a couple weeks ago of 26 and 29 degree temperatures.  Several of my trees showed immediate signs of frost damage, some seem to be totally fine, and these crabapples just started showing the brown, wilted leaves within the past day or two.  I'm concerned because it looks like fire blight, even though I have 20 young fruit trees on my property, and have never had fire blight since planting the oldest of them 3 or 4 years ago.  These 3 crabapples were planted in the spring of 2022 and have done great ever since.  They leafed out really well this spring, and bloomed very nicely.

If I can ask a related question...I also planted 2 Yoshino cherry trees last this past winter.  They, like everything else, leafed out early and then were hit with the hard frost.  One of those trees has completely recovered and has grown new shoots and leaves, but the other one, which is only planted about 30 feet from the other one, has not done anything yet.  It just has the shriveled up dead leaves on it, and has not started to sprout new growth yet.  These were both planted as bare root plants, and are just a little over 3 feet tall with trunk diameters of about half an inch.  Is it possible that the one tree was killed, or could it just be taking a lot longer to bounce back from the frost damage?  I don't have any pictures of the Yoshino cherry tree.  All of the attached pictures are of the crabapples.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 17, 2023, 4:19 PM EDT
response: We think the damage pictured might be both -- overlapping symptoms of Fire Blight plus cold injury from late frosts. In recent days we've received several inquiries about trees with Fire Blight symptoms (crabapples, apples, pears, etc.). If you are preventatively spraying your fruit trees for the typical pests and diseases encountered in our area, as is recommended, then you are probably protecting them sufficiently from Fire Blight infection.  One way to distinguish between cold injury and infection is waiting to see if new growth appears after the damage manifests. If only cold-injured, branches with leaf damage will regrow; if infected, they will not, plus decline can continue as the bacterium moves further down the branch and deprives more growth of water and nutrient flow.  One of our tree/shrub reference books that includes Crabapple variety rankings does list 'Snowdrift' as ranging from having moderate to high or even severe susceptibility to Fire Blight. Other sources do mention a vulnerability to this disease for 'Snowdrift' but don't list how severe it might get.  It's hard to tell if the second Yoshino cherry you describe is dead or just weakened enough that it isn't ready to leaf back out yet. Plants tend to lose freeze/frost tolerance once they break dormancy, no matter how prematurely that dormancy might be broken due to a warm spell, so it's possible the sapwood in that young tree couldn't withstand the temperature drop. Frost pockets are places in the landscape that collect colder air (because it sinks down into low points between hills, for instance) and if one tree happens to be planted in one, if the ground isn't fairly level there, maybe that influenced its ability to tolerate the temperature swings.  Perhaps something unrelated to (but overlapping with) the frost damage is preventing it from recuperating. Is the plant surrounded by lawn, where maybe mowing or string-trimming damaged the bark on the trunk? (Such injuries can kill a tree.) Perhaps it had unhealthy roots or not enough roots when planted, since bare-root plants are more perishable than containerized plants since they can dry out easily prior to planting. Maybe it was over- or under-watered around the time of the frost, or roots were struggling and, without the support of carbohydrates from photosynthesizing foliage feeding new growth, couldn't replace any lost roots or establish new ones. Time will tell if the leafless cherry can recover, but if you don't see new growth fairly soon (by late May or early June, maybe, given your location in western MD), it might have been lost.  Miri

responder: The Question Asker Replied May 18, 2023, 8:47 PM EDT
response: Good evening,    Thank you very much for your quick response to this question, and to my question about the scale insects on my young oak tree.    I will keep a close eye on the crabapples to see if it looks like any regrowth is starting to happen now that it looks like we will have a stretch of warm weather.  I have not seen any signs of fire blight on any of my other fruit trees, and I do have 6 apple trees and 2 pear trees, so they could be susceptible to it.  Also, the fruit trees are located in between the crabapples, so I would think if there is an infection spreading around it would have gotten at least one of the fruit trees.  The other thing is that all but two of the fruit trees have been in the ground for 2 years or more, so they are probably better able to deal with things than the crabapples that were just planted a year ago.    I have not started a spraying regimen for my fruit trees yet.  The oldest ones were planted in September 2020, and the most recent one was planted early this spring.  I have not had any disease problems so far, other than a little cedar apple rust last year.  I removed the infected red cedars from my property over the winter, and so far I haven’t seen any signs of it on my trees this year.  So, I guess I should look in to the spraying schedule to try to protect things a little better, just in case.    The two Yoshino cherry trees were just planted this spring.  They have trunk guards on them, and are surrounded by mulch beds about 24 inches in diameter, so they haven’t been damaged by a weed whacker or lawn mower.  I guess the more likely scenario for them is that one of them was just more healthy and/or had a healthier root system when it was planted and was better able to recover from the frost.    So, I’m watching all of those things closely, and keeping my fingers crossed that they will all recover.    Also, I removed all of the scale insects from the oak tree that I asked about in a separate question.  The tree is young and only about 5 feet tall, so it was easy to reach all of them and get them off.  The worst thing was that the tree is about 5 feet away from a nest box with tree swallows in it, and I was being dive-bombed by an angry bird the whole time I was removing the scale insects!    Thanks again, Jason

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 19, 2023, 3:03 PM EDT
response: Hi Jason,  Fruit tree vulnerability to fire blight and other diseases varies from one cultivar to another, and may also depend on exactly when they were blooming (as the spores are through to primarily be introduced to the plant on pollinators visiting the open flowers). Therefore, it's conceivable that the crabapples got hit hard this year while other fruits nearby avoided infection. In this situation, how long the trees have been in the ground is likely not a factor, though it might impact other forms of tree stress susceptibility.  Our When to Spray Fruit Trees page provides illustrations and brief descriptions as to the types of certain stages of growth referenced in most spray schedules. These are used more so than calendar dates because weather variations will cause trees to break dormancy at slightly different times each year, which in turn impacts when pathogen spores will be on the move. Trees are vulnerable to different pathogen spore infection at different times, though overall these windows of time tend to overlap in spring, though might extend into early summer. Spraying manages pests too, so some of these will also be applied at specific times, which relates to the insect's life cycle and what life stage does the damage. Sometimes new fruit tree plantings escape significant pest/disease problems in their first few years if there aren't many fruits in the immediate area (so the insects or pathogens have to "find" the hosts) but eventually they tend to catch up. Be advised that while removing rust-infected junipers in the immediate vicinity of vulnerable fruits is prudent, spores of rust fungi can travel for a mile or more on the wind, so future reinfection is always possible.  Mulched zones around trees is great but just make sure that the mulch doesn't touch the trunk itself, leaving a bit of a void in the center so the bark is uncovered and continues to get good air circulation. (That is, don't use a "mulch volcano.") The mulch layer should be a flat three inches deep or less in order to not suffocate the roots.  Some birds do actually consume scale right off the branches, but we don't think Tree Swallows do since they prefer to catch insects in flight. Hopefully the parent birds weren't too perturbed afterwards. Good luck!  Miri

responder: The Question Asker Replied May 19, 2023, 3:50 PM EDT
response: Hello! Thank you for the great additional information.  That will be very useful. Yes, I definitely keep the mulch away from the tree trunks, and don't employ the mulch volcano strategy!Thanks again!JasonOn Fri, May 19, 2023, 3:03 PM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 19, 2023, 4:06 PM EDT
response: You're welcome!

responder: The Question Asker Replied May 22, 2023, 8:23 PM EDT
response: Hi, Miri.    I just wanted to give you an update on the latest with my crabapples and Yoshino cherry and see what you thought.  After looking at the information you sent, as well as some other information online, I felt pretty sure that the issue with the crabapples is fire blight.  I also read about some management techniques, including ugly stub pruning, etc.  I understand the rationale for that, but since these trees are so young the affects of the fire blight already reached most of the length of each affected branch.  I was hoping to just prune it all out of the trees.  I have done a lot of hard pruning with the other fruit trees that I have planted, so I was hoping that I could take advantage of the long growing season ahead of us and just prune them back hard and see how they respond over the summer.  If I end up losing them, it was probably heading that way anyhow given how much of the trees were affected.  I would prefer to be aggressive this year and hope for the best, than to be conservative and end up losing them next year or the following.    Regarding the Yoshino cherry tree, it still hasn’t put any new growth out yet, but I have done a couple tiny little scratch tests on the bark over the past few days, and there is green tissue just under the brown bark, so I guess that gives me a little hope that it still may be summoning the strength to bounce back.    Anyhow, that’s the latest on those two issues.  Thanks again for your help!    Jason

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied May 23, 2023, 3:31 PM EDT
response: You're welcome. Good luck! The lack of foliage on the cherry is not encouraging and while a scratch test can sometimes be unintentionally misleading and giving false hope regarding the potential for regrowth, all you can do is give them a bit longer (until the scratch test doesn't reveal any green tissues) if you want to be certain it's a lost cause. If keeping them isn't holding-up a process for replacing the trees, there's no harm in waiting a little more.  Miri