Why are my high bush blueberry plants not doing well?
Question:
I planted six high bush blueberries of different varieties three years ago. This year several of them are growing strangely. Some have a ton of berries, but minimal plant growth. Others had hardly any berries and others appear damaged or sick. Could you provide potential diagnosis and guidance as to how to help them?
Answer:
So, I think we have two separate issues here.
1) Variability of fruit and leaf production. This can depend heavily on how the plant allocates its resources into different plant organs. Blueberries form buds for next year on current season wood, so a proliferation of leaves or fruits indicates that last season the plant was pushing resources into bud formation for one or the other. We had a number of late, hard frosts at the end of the 22-23 winter that caused a lot of bud damage, so this may have factored in. Best practices management will keep the shrubs healthy overall and average out the production over time.
2) Foliar issues. All of the above said, you definitely have something going on in the leaves–I’m seeing what might be evidence of anthracnose and septoria, though visual diagnosis is always tricky. You will want to prune out affected leaves and branches, remove all fallen plant debris from the bed (many fungal pathogens will overwinter on plant material in the soil), and clean/sterilize your tools between shrubs to prevent spread. Also moving forward, if you do any supplemental watering, make sure it’s aimed at the soil below the bush and not over the top. Moist, still air in the interior of the blueberry helps spores proliferate, so you want to avoid unnecessary wetting. If the conditions continue next year, you could consider using a fungicide, though these are mostly preventative rather than curative, which makes it tough to decide if you need to use one.
Both of these issues will also be mitigated by proper pruning of the shrubs, which will remove problem tissue, keep them healthy over time, and increase airflow through the leaves, which helps tamp down fungal spread.
As I indicated above, visual diagnoses are inherently challenging, so if you remain concerned or if my advice doesn’t seem to match what you’re seeing, you can always consider submitting the photos and a physical sample to the UMaine Plant Disease Diagnostic Lab for testing. There is a small fee for their service, but you’ll have confirmation of any pathogens present. I lean toward encouraging you to do this because I’m on the fence as to whether I’m also seeing some cankers on the shrub stems–it might be good to get a second opinion from the plant pathologist at the lab.
Happy gardening.