From one of the coldest Aprils to one of the hottest Mays, what will June bring us? So far, apple scab has been less of a problem than usual, but powdery mildew seems to flying under the radar for many orchards. Keep your eyes out for the characteristic leaf curl (Fig.1). Varieties like Jonathan, JonaGold, Cortland, GingerGold and SunCrisp, are very susceptible. Due to the dry weather, many growers switched to a captozeb program, which is excellent against scab, but doesn’t do anything for powdery mildew, or very little against rust.
Fig. 1. Typical leaf curl from early powdery mildew infection. Photo by Janna Beckerman.
Speaking of rust: Dry weather has delayed not only ascospore ejection of scab, but also those orange, gelatinous kooshballs of spores (Fig. 2). I don’t recall the last time I saw any telial spore horns (aka kooshballs) in June, but they were still going like gangbusters on June 1 here. For those in central Indiana to parts north, all three diseases are controlled by strobilurin/QoI fungicides like Flint or Sovran; 7-11 fungicides like Luna Sensation, Merivon, Pristine; or DMI fungicides like Indar, Inspire, Rally and Topguard. Of course, depending upon fungicide resistance issues, your mileage may vary.
Fig. 2. Juniper rust, specifically, cedar-hawthorn rust. Photo by Janna Beckerman.