Due to the effects of the unusually warm winter, I am not offering spraying of copper sulfate for ornamental fruit trees for spring 2024. Instead we will have to make 2024 a case study: What happens if we don’t spray copper for a year?
A critical first copper application is best made as the buds show a “green tip” of growth, which is already happening as of March 6th. Typically this doesn’t happen for eight more weeks–at the end of April! As I am writing this, overnight temps have dropped to 29 degrees, which means that leaf and flower tissue may have been frozen, further suggesting that the tree may have to tap the roots for energy to regrow new buds (commonly, a month later). An early April re-budding could also be so early that that too could be vulnerable to a freeze, in which case the trees would have to come up with even more extra energy from the roots to produce buds yet again. So it will be interesting to see what the weather brings and how the trees react. It is impractical for me to try to guess as to how this will play out and when I should try to spray copper! In summary, from a business standpoint, this is too operationally complex. But this will be a great opportunity to observe the effects of unusual warm (and perhaps more drought) on disease and pest life cycles of fruit trees (and about trees generally).
The copper fungicide application is often made largely for aesthetic purposes–to keep the leaves from shriveling up in late summer and littering the lawn, leaving you with a leafless tree for the last couple months of the growing season. Because this happens year after year, there are presumed cumulative stresses on the tree, perhaps from excess summer sun on the otherwise shaded bark, which may be avoided with the annual use of copper. It’s worth noting that spring 2023 was unusually dry, and of course “dry in spring” is rather unusual–and fraught with peril. It is known that the rust affecting fruit trees spreads in connection with rain. Since we can never predict “how much rain” we will get in April and May, we are applying copper in early spring before we know how necessary it is to do so in any given year in order to avoid the fungal infection on the leaf. I have been applying copper to most of your trees for several years, such that you have been able to note whether or not the copper is having, generally, a positive effect. Had we known that last year was going to be so dry in the inoculation phase of this pathogen, we probably wouldn’t have bothered with the copper.
We really have no choice this year but to skip the copper for the reasons discussed above, but we can make an experiment of seeing how your trees look in late summer–to see how much leaf rust they have. This is a rather convoluted experiment, however: At the moment we do not know whether buds will freeze and have to be regrown once, or twice, or not at all. We do not know whether or not we will have a wet spring in the period that the fungus is transported through the air and encounters your trees developing leaves. In short, fruit trees and trees in general face potential stresses which are far greater than Apple-Cedar and Cedar-Hawthorne Rust.
In the life sciences, hindsight is 20/20! To that ends I will welcome and appreciate your observations of your trees this spring and late summer in comparison to copper treatment years and years prior to copper treatment. Send me a text/photo at any time with your updates. My end goal of course is to learn about tree disease phenomenon, such that I can make even more informed plant health care decisions for my customers in the future.
Click here for a good academic article explaining Cedar-Apple Rust from Oklahoma State University.
Thanks, and as usual, call or text with any questions. I will likely have a pitch for copper spraying of your tree(s) at this time next year….
–Will
