Apple Disease Update: Week of July 20, 2025
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It’s that time of year where the excellent treatments for managing Glomerella leaf spot and bitter rot separate themselves from the imposters. Fungicide applications for the tree on the left (Captan 80WDG) were initiated at 5th cover (~35-40 days after petal fall), whereas applications of Captan 80WDG were initiated at petal fall for the tree on the right. For both treatments, applications occurred on a 7 to 10 day intervals once they commenced. Although the lighting in the photo has much to be desired, it’s clear that the level of defoliation is much greater for the tree on the left. As I’ve mentioned previously, a number of trees in this research block are now dying or declining; likely from repeated years of premature defoliation due to GLS leading to a decrease in cold hardiness and increased susceptibility of opportunistic fungi such as Botryosphaeria. Furthermore, the trees are old in apple years-the orchard was apparently planted in 1997….
Like I said above, given this hot, humid and occasionally rainy afternoon weather over the past couple of weeks, as ‘Gala’ approaches maturity we are beginning to see significant differences in our GLS and bitter rot fungicide trial. For example, the incidence of GLS in the Omega fungicide treatment had minimal disease incidence; however while I haven’t crunched data yet, Captan 80WDG treatments that were either initiated at late bloom, petal fall, or first cover appeared to have considerably less disease incidence on the leaves. It’ll still be ~ 2 weeks until fruit rot incidence data is taken, but I will update you on these results as soon as I have them. As you can see in the photo below, incidence and severity are right on par at our research orchard in compared to other years.
For this week, continue to keep tight intervals with Captan 80WDG or Captan 4L. We’ve been applying 2.5 lb/A of Captan 80WDG in our research orchard; the station has been applying 2 qt/A of Captan 4L. If you need something with a bit more kick consider Topsin for GLS and bitter rot associated with GLS, Merivon, Pristine, or Aprovia. Remember that Aprovia has a 30 day PHI so you’re likely cutting it too close on early-harvest cultivars. Also, I like saving Merivon for my final spray for a particularly cultivar (or prior to your biggest pick).
Some Important PHIs to Consider:
- Aprovia: 30 days
- Omega: 28 days
- Luna Sensation, Flint Extra: 14 days
- Inspire Super: 14 days