Major Apple Scab and Juniper Rust Infections Predicted 14-17 April in Whole Virginia
Apples are in bloom in Winchester and from 14– 17 April 2023, and besides fire blight threat I addressed in my previous blog post from today, we are expecting multiple rain events as per the NWS forecast. These many rain events will allow longer leaf wetting that will lead to major scab infection in whole VA, and especially in and around the Winchester VA. This also be a sever rust infection event. I would recommend to be covered with at least 3 lb of Mancozeb Pro-Stick, but adding a DMI fungicide otherwise know as SI fungicide, will be a wise choice in all of Virginia apple orchards. It varies depending on a location, but the current scab model prediction indicate that the scab infection will start with the rain on 15th or 16th April early in the morning (~ 9 AM) and multiple other infections will occur with the rain events on 15, 16, 17, and 18April. This will surely cause significant apple scab fungus ascospore release and infections in northern Virginia. These are my spray recommendations:
A good spray period will be from today 14th or tomorrow 15th April before the rain on 15th starts and any time during 16th April when leaves dry a bit, because you would achieve maximum coverage of the rapidly expanding green tissue. If you must, you can also apply a DMI fungicide up to 96 h after the infection started on the 15th April but we would not recommend this kick-back application mode and we would recommend it only in an emergency (no spray coverage before 15 April; sprayer breakdown, etc.) . The best option to apply would be Inspire Super (12 fl oz/A), or Cevya (5 fl oz/A), or Procure (16 fl oz/A) plus mancozeb (3 lb/A). Keep in mind that the systemic fungicides here are preferred for severe scab events like this because with warmer temperatures the green tissue will increase its surface area intensely from 6 – 9 April (1), and the DMI will enter inside leaves while they expand and protect them through the multiple rains (6 events). The idea is to have enough fungicide residue cover to stay on the leaves through the infection periods even if rains top up to 2 inches (up until rains end on 18th April). If rust is not of a concern for your location, as maybe no cedars are close to you, mancozeb (3 lb/A) plus Luna Tranquility, or Fontelis, or Aprovia, or Sercadis, or Miravis, or Excalia, would be a better choice for scab control (all these single-site SDHI fungicides will not be effective on juniper rusts, but they will control powdery mildew). I would not recommend you to apply SDHI after the infection on 15 April (kick-back mode of use). You can, if you must, apply Luna Tranquility after the infection due to an Anilino Pyrimidine (AP) component in it that has kick-back activity up to 72 h (pyrimethanil). Make sure you apply it up to 72 h after the rain starts early morning on 15th or 16th April.