Apple Disease Update: Week of June 10

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Image of a diseased apple

The past week has been relatively uneventful in regards to infection events compared to previous weeks. That said, relative humidity, leaf wetting hours, and temperature was within the parameters for a Glomerella leaf spot infection event this past Sunday (6/10) in Western NC. For this week’s post my goal is to keep management suggestions short and sweet:

Glomerella Leaf Spot/Fruit Rot: Even though there was less than two inches of rain in Western NC this week, I would encourage an application of Captan 80WDG (3.75 lb/A) + ProPhyt (4 pt/A) or Ziram (4 lb/A) + ProPhyt (4 pt/A) no more than 10 days after your last fungicide spray. In both our research orchard and in commercial orchards, using a 14+ day application interval even during drier summers was too long. Given the humidity and leaf wetting hours often experienced during the summer months in NC, these conditions may need enough to trigger an infection event. Applying ProPhyt or a different phosphorous acid fungicide seems to enhance the activity of captan (or has in the very least provided greater control of Glomerella leaf spot/fruit rot than captan by itself. So far I’ve seen a bit of GLS in Henderson County, but little to no fruit infections in orchards that I’d visited.

Bitter Rot: Technically bitter rot is a more general term that includes what I refer to as Glomerella fruit rot. In other words, Glomerella fruit rot is technically bitter rot. The same fungicide programs for “Glomerella” should also be used for “bitter rot” in apple. In visiting apple orchards today, I noticed several apples (I presume they were hand thinned?) laying underneath tree canopies in some blocks. If you have had a lot of bitter rot pressure previously in certain blocks, I’d encourage you to remove the fallen apples from the orchard and destroy them. Bitter rot will often develop on these fallen apples. Spores from these infections can be splashed dispersed into the tree canopy or possibly be even vectored by fruit flies or other insects into apples within the tree canopy.

I think that’s it for this week’s update. As always, feel free to email me or call me with any questions that may come up!