Source: NCSU COOPERATIVE EXTENSION, 8/24/21

As Gala harvest concludes (and now that I’ve been able to do some additional research) this week I’d like to address two main topics. The first is going back to the question posed a few weeks ago: Do we need to continue to spray for Glomerella leaf spot following harvest? In short, my advice would be to continue to spray a protectant fungicide (e.g. Captan) every 14-21 days following harvest on Gala or cultivars harvested within a few weeks of Gala. I’d particularly advocate for this if you have incidence on your trees less than 20% or so. Anything more, my thought is that any overwintering inoculum is likely going to be quite high (prior to interventions such as flail mowing and urea applications) that it’s not likely worth your effort or money.

I promise the reasoning behind this advice is not because I enjoy watching you juggle harvest and additional applications at the same time. During the past week I have gone and sampled leaves with GLS lesions from the leaves and the ground. In both locations, there was evidence of acervuli (the fungal structures that contain the asexual spores of the pathogen-see photo directly below). When I ruptured the acervuli, mature conidia (those asexual spores that appear salmon/orange on bitter rot lesions on fruit) were discovered. This means that pathogen is still out there and able to infect (as evidenced by the lesions on young leaves in the top photo).

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