Yoshino Cherry Decline?

Question: We planted a 2 year old yoshino cherry tree, obtained from our local nursery, last spring. It seemed to have established well during its first season. We got ample blossoms a few weeks ago when it flowered but as it transitioned to leaves we noted that several branches seemed "withered" at the ends with no new leaves growing and signs of what appeared to be leaf buds having died. On some of these branches there are new leaves beginning to come on but only about 1/2 way out the length of the limb/branch and it is only about 25% of these "withered" branches displaying this behavior. This tree gets ample sun, about 6-8 hours a day, and we try to monitor the water it gets. Overall, this tree doesn't appear to be thriving and we are concerned something is wrong. Can you look at our pictures and help us determine what this tree needs to be healthy? It was hard to get good shots so we have fingers crossed that you can gleam something from what is there. Thank you!

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 12, 2023, 2:21 PM EDT
response: It's hard to tell from the photos what is affecting the tree, though we think we see (it's dark and hard to make out) old cicada egg-laying scars in some of the leafless branch tips. This would be expected for a tree of this age since the periodical cicadas causing this damage emerged a couple years ago. Some tree branches tolerated the damage but others succumbed to dieback either immediately or within a few years of the damage occurring. You can visit the linked page to see if the scarring looks similar to what might be on the underside of those leafless twigs.  Regardless of the original cause, the branches lacking leaves at this point should be pruned off, down to wherever they meet live growth. Be sure to leave a short stub at the juncture instead of pruning branches off flush with the trunk (or with larger branches where they meet) as this type of wound will not seal-over well and could invite further dieback. The "proper pruning cuts" section of our tree pruning page illustrates where to make a cut so the branch collar (the zone of tissue that will close-over the cut) is undamaged.  Root loss can also cause branch dieback, though it can be hard to trace-back when that might have occurred since the impacts aren't always immediate. Cherries are sensitive to over-watering and poorly-drain soils, though in that case we think the damage might have been more universally impacting all branches. In either case, we see the outlet of a roof downspout and what might be a sump pump outlet somewhat close to the tree (uphill from it?). Make sure this doesn't deposit too much water into that area during heavy rains, or else see if you can extend it further away from this site. To determine when the tree might need water based on weather, feel the soil around six inches deep. If it's becoming somewhat dry to the touch at that depth, watering will probably benefit the tree. If it's damp to the touch at that depth instead, watering is probably not needed yet.  We can't see the tree's base in the photos, but if the lawn grows up to the trunk with no mulch barrier between them, we suggest using one. This will not only reduce the odds a mower or weed-whacker strike causes serious injury to the vital sapwood just under the bark, but will also reduce competition between the tree's roots and the lawn's. (As the tree matures and casts more shade, it will gradually cause the turf to thin-out anyway.) Mulch should only lie in a flat layer about two or three inches thick and should not touch the trunk base itself so it gets good air circulation. Planting depth is also critical for trees, even if impacts from improper depth don't manifest for years. The root flare, which is the point on the trunk base where major roots branch off, should sit just at the soil surface. If buried by even a few inches, it can lead to problems with root health that can cause canopy dieback.  Ornamental/flowering cherries are unfortunately vulnerable to an array of potential problems, so overlapping issues might be contributing to its struggles. While possibly too young yet to have attracted the attention of a wood-boring insect, we can't rule it out, nor can we rule-out an infection by fungi or bacteria that kill or clog the water-transport tissues within the branches, both of which are factors that can cause them to wilt or have their leaf buds die so the branch can't leaf back out. You can explore our ornamental cherry diagnostic page for possible culprits to see if any symptoms seem to match.  Little can be done about existing issues since pesticides in this situation are preventative, not curative, but since trees under stress tend to be more vulnerable to problems overall, monitoring the plant's watering needs and not fertilizing it (it will be getting plenty of nutrients if you fertilize the lawn yearly) is the best thing you can do for now. Time will tell if it's able to recover; at least ornamental cherries tend to grow relatively quickly when healthy, so it can catch up if whatever the problem is was temporary.  Miri

responder: The Question Asker Replied May 13, 2023, 6:48 AM EDT
response: Thank you for your email. After reviewing what you wrote and the link to the diagnostic page we are still a little lost.  We do remember that around the time the tree was leafing out we got just over 3 inches of rain in about 48 hours. Is it possible the tree just got too much water at a critical time in it's spring development?  We looked the tree over again closely and we don't think we see anything similar to the conditions on the diagnostic page. I'm attaching new pictures for your reference of both some braches, strange white dots on upper trunk and one larger spot on the lower trunk that appear questionable. The branches with die back are still flexible, should we still prune?  We thank you for continuing to guide us on this, we truly hope we can help this tree recover and thrive. Sincerely,Heather

responder: The Question Asker Replied May 13, 2023, 6:48 AM EDT
response: Thank you for your email. After reviewing what you wrote and the link to the diagnostic page we are still a little lost.  We do remember that around the time the tree was leafing out we got just over 3 inches of rain in about 48 hours. Is it possible the tree just got too much water at a critical time in it's spring development?  We looked the tree over again closely and we don't think we see anything similar to the conditions on the diagnostic page. I'm attaching new pictures for your reference of both some braches, strange white dots on upper trunk and one larger spot on the lower trunk that appear questionable. The branches with die back are still flexible, should we still prune?  We thank you for continuing to guide us on this, we truly hope we can help this tree recover and thrive. Sincerely,Heather

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 15, 2023, 2:44 PM EDT
response: Hi Heather,  Although most of the photos are unfortunately not in focus enough to clarify diagnosis, we can tell from the close-ups of the leafless branches that they are dead/dying and not going to regrow. The bark on the branches in question looks a bit shriveled or puckered, which is one telltale sign a branch is slowly dehydrating as it dies. It might not be brittle yet as this does not happen rapidly, but even supple branches can sometimes be dead. So yes, we'd still recommend that any branches which remained leafless this spring be pruned off.  Usually, when scattered dieback like that occurs, something hampered or entirely cut-off entirely the part of the tree's vascular system that's feeding that branch. The vascular system is the water- and nutrient-conducting tissues that lie just under the bark, somewhat akin to bundles of straw-like tubes, and whether physically injured (by cuts through the bark or chewed-into by wood-boring insects) or blocked internally (clogged) from fungal or bacterial growth in those tissues themselves, once the twig's leaves or buds beyond that point lose their supply of hydration and nourishment, they die and the branch soon follows. It can be hard to trace-back where exactly the problem occurred, and complicating matters, sometimes it's all the way down in the root system instead, where the loss of some roots means all of the canopy can't receive its usual amount of nourishment and water. This is not because the soil itself is lacking moisture or nutrients (so adding more has no benefit), but rather because the plant can't absorb what it needs and/or transport it to all the above-ground growth.  In a poorly-drained soil (including one that is compacted, as compaction worsens drainage), a lot of rain in a relatively short amount of time could indeed contribute to root loss from lack of enough oxygen in the soil for them to access. (The pores between soil particles are filled with a mix of air and moisture in soil that is neither parched nor flooded. As moisture levels increase, the oxygen content in those pore spaces falls because water is taking-up some of the spaces that air used to, and roots can start to "suffocate" after prolonged wetness, becoming more vulnerable to root-rot pathogen infections in the process.) If root rot did set in, no treatment will reverse it, and while there are soil-applied fungicides ("drenches") that can suppress these pathogens, they can neither salvage a declining plant nor eliminate those microbes for the long term, which is why we don't recommend their use. Root-rot pathogens are ubiquitous in our environment but they generally only cause problems when certain conditions stress a plant and make it vulnerable to attack.  We think we see a very small number of White Prunicola Scale on the bark (photo file name ending in -555) but the population size visible is nowhere near the levels that would be expected if they were causing branch dieback, so it's likely a coincidence that they are present. In fact, it's nearly impossible to tell in photographs if a scale insect is still alive since they are hidden from direct view by their characteristic covers (the shell-like layer, white in the case of this scale species, that sits atop their flattened tiny bodies). Therefore, the scale in the photo might not even be alive any longer, even if their white covers haven't weathered away yet. It's something to keep an eye on for the long term if the tree recuperates, but for now we see no need to be concerned with insecticides for treating them.  The scar on the trunk (photo ending in -416) is hard to diagnose since it appears to be old and might not have caused serious damage at the time. It could be canker -- we can't rule that out -- but if so the entire canopy would probably be in decline instead of scattered single branches. Cankers are infections of the tissues just under the bark and can be bacterial or fungal in origin. They are not treatable once the damage is done, though canker-causing pathogens tend to take advantage of trees under stress from environmental conditions like drought or injuries to the bark.  We can't see enough detail for the larger white dots (photo ending in -370) which might be what you're describing on the upper trunk, so please send in-focus pictures of those if you can. They might just be silken insect or spider constructions that are not plant pests. Some species of scale insect can be about this size, but from what we can see so far, they do not appear to be scale.  Miri