Possible Apple Scab Infection Predicted with Rains 17 & 18 March in Southeastern, Eastern and Central Virginia: Bristol, Tyro, Rustburg, Red Hill, Timberville, Quicksburg
If the weather forecast is to hold up and become true for the next 72 h, with warm rains we will get on 17 and 18 March a weak to mild apple scab infections in Southeastern, Eastern and Central Virginia, unless fungicides are applied. The stations I checked in NEWA scab model indicate that apple scab infections are to occur on any exposed apple bud green tissues anywhere close to and in between these locations in VA: Bristol, Tyro, Rustburg, Red Hill, Timberville, Quickburg (use NEWA scab model to see any other station near you: https://newa.cornell.edu/apple-scab , see printouts below). My recommendation is to apply the anilinopyrimidine (AP) fungicide like Vangard (3 oz/A), or Scala (5 fl oz/A), or Luna Tranquility (12 fl oz/A) in tank mix with mancozeb (3 lb/A) before this block of rainy weather for maximum efficacy. Luna Tranquility has two scab active materials in it: an AP pyrimethanil (Group 9) plus an SDHI fluopyram (Group 7). So far the NEWA scab model is not showing that infection is possible in Winchester and surrounding areas, and the reason why is that the rain is not predicted for 17-18 March to occur. If this prediction stays this way and becomes true, for orchards near Winchester, VA, at this moment, no infections warrantying a fungicide application are predicted. But that is why you should watch the scab model in NEWA daily and if that prediction changes and you do get the rain on 17-18 March, apply a kick-back material like Vangard (3 oz/A), or Scala (5 fl oz/A), or Luna Tranquility (12 fl oz/A) with mancozeb (3 lb/A) after this block of rainy weather.
The above recommended AP fungicides work well in the periods with swings in cool and warm weather in spring like now and can be applied before or up to 72 hr after the time when rain event began which triggered the scab infection (kick-back activity), however, use the kick-back mode of activity only in an emergency i.e. if you know you did not have any fungicide applied before this infection. Vangard (3 oz/A), Scala (5 fl oz/A), or Luna Tranquility (12 fl oz/A) with mancozeb (3 lb/A) should be applied once more (at Tight Cluster) and keep in mind that they are not effective for juniper rusts but that is why you are adding mancozeb. This multi-site contact fungicide will wipe out any rare early rust infections at Tight Cluster, but plant to apply DMI fungicides (Group 3) at PK bud for rust if galls on nearby cedars open.
Finally, besides paying attention to temperature, rain, and hours of leaf wetness, the amount of green tissue surface present a the time of infection on your trees, is CRITICAL. The more the apple leaf tissue expands the higher the risk for infections will be. If you had scab symptoms last year in your orchard, you should count that you have high levels of carry-over scab inoculum from the infections of the previous year. Here are the outputs from NEWA for he locations I listed above for 17 – 18 March: