This newly planted Bloodgood has started to show light brown spots this growing season, and is not leafing out quite as vigorously as I would have hoped. I assumed it was drought-related (it's in the shadow of two massive poplar/locust trees), so I increased my watering time, but my neighbor thinks it's fungal disease. Thoughts? I sprayed with Bordeaux, not much else to do I imagine.
Has the look of phyllosticta a fungal disease. Regular watering and mulching is the best way I have found for this. Also make sure leaves that drop are destroyed and not left to rot over winter.
One thing we noticed over the years with newly planted Japanese maples from retailers was the same type of issues you are showing. Often young trees are grown in green houses, then transported to retailers for sale. After abruptly being exposed to outdoor sun and spring rain showers ( water drops acting like a magnifying glass) this was a very common look to the leaves. The sudden shift from being in a protected environment to full on sun on delicate new leaves does show those same type of symptoms. A good chance it will adapt and recover naturally. Watch for the next flush of new growth and that may ease your concerns.
This is still widely believed but has been proven to be a myth. https://gardenprofessors.com/water-droplets-and-burned-leaves-continued/
@Margot , I just read the article. Seems to relate to the natural growing environment of plants in general and how water is and can be dispersed on specific plants. In our experience, we would have approx 6-700 young grafted trees of many varieties ready to move outside from the greenhouse in early April to the shade houses we had built. We would always baby them as they had to be just perfect for the annual Van Dusen garden show in Vancouver back in its prime. Often our shade houses were too full so up to 100 cultivators had to sit in full sun. These trees were already 2-3 weeks ahead in leaf formation then all the field grown trees. It never failed that we would get the brown spot / holes in some of the trees not protected by the shade house. Of course those never made it to the garden show. We would sell them once the next flush of growth came out. Personally I do not think it is a myth at all. When trees are grown in an artificial surrounding and not allowed to evolve naturally with the spring weather, the foliage is weaker and often can not withstand the quick change. The worst was always a sudden spring rain followed by very excessive heat on the same day. With that said, we never had an issue with any of the trees that were damaged, they always rebounded back with the second growth flush. Also our experience is only in growing japanese trees and the effect it had on young cultivators removed from green house to an outdoor environment in early spring. All the shade house stored trees never had the brown spot / hole issue, they would receive the same rain, but very limited sun. And perhaps it is not the right choice of words ( magnifying glass), but rather the effect sun and rain had on very tender leaves that were not hardened off with a natural spring growth rate. I guess it could be a very limited study in that sense
Certainly looks like Phyllostica to me, now that I look at more examples. In addition, I've noticed the same spots on a sheltered, mature Red Dragon on the other side of the property. So I presume I just drown them in copper and hope for the best? :)
Not so sure about drowning in copper. This can affect the natural organisms in the soil. I use Bordeaux mix on cut stems, but that's it. So if you decide to prune out some of the branches that die back, then apply the paste. As I said, a good mulch with a regular but controlled watering regime and removing and destroying any fallen leaves should sort this problem out. The second flush will give an idea if all is heading in the right direction. I wouldn't rule out @Otto Bjornson theory though, he has decades of experience growing maples to sell, so keep an open mind. @Margot also makes a very good point re the study she has attached. It is very much science theories, when not all experts agree with each other.
Experts agree when peer-reviewed studies reach the identical conclusions. It doesn't look like there are many studies so far about the theory that water droplets burn leaves. I think this one is quite compelling and allows for the fact that water droplets on smooth leaves can have a different effect than those on hairy ones. Are Japanese maple leaves considered to be hairy? "In sunshine, water drops residing on smooth, hairless plant leaves are unlikely to damage the underlying leaf tissue, while water drops held above leaves by plant hairs can indeed cause sunburn, if their focal regions fall on to the leaf blade." https://nph.onlinelibrary.wiley.com/doi/full/10.1111/j.1469-8137.2009.03150.x
They are smooth... But the point I was making is that many scientists disagree on test results that are identical. I understand peer reviewed. So what I was saying about Otto's post, was that in the real world for many decades of growing Japanese maples he had come to the conclusion that indeed water droplets on very young maples would cause spots on the leaves from direct sun. I do like to keep an open mind between science and practice. As usual, a very good point made by you Margot.
A droplet of water on a leaf is likely not pure water. In addition to pollen, bacteria, spores, and the like are 'always' in the air. They will wind up suspended in the water standing on a leaf. BTW, most fungicides work by being a dry coating on leaves and stems that is activated by becoming re-dissolved in water that comes to those surfaces. It just kills the spores in that water droplet. I happen to be a fan of dilute hydrogen peroxide spraying because it is inexpensive and enviro-friendly. Its shortcoming, however, is that it only works against the spores that were present at time I sprayed. It leaves no residue that can affect anything that shows up later.
I generally use an "organic" copper spray like Captain Jack and tend to use it liberally. But I'll be sure that no leaf clutter remains on the ground.
Now that's a very good point, I wonder if that was taken into consideration in the study that @Margot posted. I didn't see it mentioned.
@MapleZen , I see this every year in CT, but this year it’s particularly bad. There is no damage long term to the trees, and I don’t treat with anything. Shirazz is affected the most this year (pictures from the beginning of June, before the forums shut down for a month). Interestingly, right next to it is shirasawanum ‘Jordan’ without a single spot on its leaves, go figure… A. griseum is also not affected. Local species, saccharum and rubrum are showing plenty of the same spots. Whatever it is, it’s just cosmetic damage.
Thanks for that confirmation. The spots sort of halted after I treated with Bordeaux (coincidence or not) and the trees seem fine otherwise, which I would expect from leaf blight. Thanks!
