14-16 April 2023 Rains: (I) Possible Fire Blight Infection; (II) Juniper Rusts Active in Central but Not in Northern VA, (III) Scab Infection Possible if Leaf Wetting is Long
We are in bloom in Northern VA. Based on the weather forecast as it stands now, if showers predicted in NWS with a 17-53% chance to occur on Saturday 15th or Sunday 16th April they will lead to infection by fire blight. The only exception is Bristol with predicted infections 14-15 April. NEWA’s EIP Model print screens showing dark red boxes and EIP over 100 are inserted below. As you get closer to 16th April, weather forecast will get more reliable and find a good window to apply streptomycin if EIP is still in dark red box and over 100. In central Virginia, Juniper rust galls are orange and will produce basidiospores that infect apple spur leaves with these rains so apple trees require protection with SI (DMI) fungicides like Rally, Rhyme, Procure, Inspire Super or Cevya. In central Virginia my recommendation would be Inspire Super 12 fl oz/A+ mancozeb 3 lb/A, or any of the other DMI’s listed above. If the current weather forecast remains as it looks now, scab infection could occur but it might not be a severe one due to fast drying of leaves after rains 16 April. Who uses RIMpro will be know. In Northern Virginia, I would recommend you to tank mix fungicides with your streptomycin to make it more economical and to control any weak rust and scab infections. A good choice in Northern Virginia would be mancozeb (3 lb/A) + either Fontelis, Sercadis, Miravis or Excalia for scab. Mancozeb will be effective for any weak rust infections. The SDHI fungicides will work better against scab by adding the adjuvant for streptomycin, and it will control powdery mildew as well. However, all these single-site SDHI fungicides will not be effective on juniper rusts, but we are counting that rust is not ready yet to infect in Northern Virginia. Fungicides are needed because leaf mass will rapidly expand with warm weather we expect and it is best to have a systemic fungicide in the green tissue while it expands. Dilution of fungicide residue is not only caused by rain, but with the leaf tissues expansion as well. Be vigilant and keep looking at the prediction models every day, twice a day (morning and evening) to see if any of these predictions will change and apply your disease control materials accordingly (for example, if rains on 16th April trigger slow leaf drying, I would replace the SDHI fungicide above with a DMI fungicide: Inspire Super, Rally, Rhyme, or Procure, etc.). A good spray period will be from 12-15 April before the rains on the 14 or 16th April start, because the closer you are to the infection period you would achieve maximum coverage of the rapidly expanding green tissue.