Major apple scab and fire blight infections predicted for 25 – 27 April 2025 rains: Powerful Spray Protection Needed

Major apple scab, Juniper-apple rust, and fire blight infections (where flowers are open) are predicted for 25 – 27 April rains ahead. See attached screenshots. This applies to all of Virginia. Apply fungicides and streptomycin tomorrow, before the rains start.Early apple cultivars are at Petal Fall in central Virgnia but many other cultivars are still in bloom in Winchester. From 25 – 27 April 2025, we are expecting multiple rain events starting during the day as per the NWS forecast visible at this moment. This is predicted to lead to major i..severe apple scab and Juniper-apple rust infection in all of Virginia. This will also be a significant fire blight infection event for any apple tress in bloom. At petal fall, I would recommend using Cevya, Inspire Super, Rally, Sonoma, Topguard, Rhyme or Procure plus mancozeb (stop mancozeb at 77 days before harvest for early maturing cultivars). This will cover you for scab rust and powdery mildew. In regions where you think Rally is not that effective add Microthiol Disperss to your spray tank in addition to DMI fungicide and mancozeb. Another tank mix consideration is either Fontelis, Sercadis, Miravis or Excalia plus mancozeb for scab, rust and powdery mildew control at the same time (most weight for rust control will be pulled by mancozeb, so use these mix in areas where rust was not a historical problem). Juniper-apple rusts can have extended infection periods up until 1st or 2nd cover in Vorginia. We are in a year with wet and warm spring when cedar galls have been out from 3 April, at least in Winchester area. Warm wet weather at petal fall can also allow Botrytis to infect the dying petals and move from petals into sepals where it can remain quiescent until fruit are moved into storage where the Botrytis can cause gray mold storage decay. Using Inspire Super at petal fall and/or first cover is be the best option because it contains cyprodinil, a fungicide that is effective against Botrytis (if Botrytis is not resistant to this fungicide). Powdery mildew can have an extended infection periods in highly susceptible cultivars until first or second cover too, so reserving DMI fungicides for use by second cover in these cases is necessary. If powdery mildew was not an issue last year, Inspire Super or other DMI plus mancozeb would also be my recommendation for the first cover (10 days after petal fall). If mildew was more of a problem last year for you, use SDHIs: either Aprovia, Fontelis, Sercadis, Miravis or Excalia plus mancozeb (3 lb/A). Add a surfactant to SDHIs as it allows their longer residual activity. For scab, consider using Axios this year – it is a new fungicide in FRAC 52 group and is very effective. Only three applications per year are allowed. Incorporating Axios into spray program will help prevent fungicide resistance to FRAC 3 (DMIs) and 7 (SDHIs). At this time of the year systemic fungicides here are much needed for severe scab events like we expect 25-27 April because with warmer temperatures the green tissue will increase its surface area intensely in April (1), and the DMIs and SDHIs (if you add attractant) will enter your leaves while they expand and protect them through the multiple rains (2). The idea is to have enough fungicide residue cover to stay on the leaves through the oncoming infection periods. If rust is not of a concern for your location, as maybe no cedars are close to you, mancozeb (3 lb/A) plus Fontelis, or Sercadis, or Miravis, or Excalia, would be a better choice for scab control (all these single-site SDHI fungicides will not be effective to control juniper-apple rusts).  This blog is based on the outputs from the NEWA apple scab model available at https://newa.cornell.edu/apple-scab

I decided not to post print screen this time as I want you to get used to using these models yourself – it is imperative that you use them and get comfortable interpreting them. If you have any questions you can contact me, using usual channels.