On Monday, March 31, we saw our first green-tip stage showing on Gala (above) and Red Delicious apples, and that raises the question whether wetting March 29-30 was enough for a scab infection period.
At our AREC, we had just enough wetting (18 hr wet at 48-40° F, with 0.54 inch of rain), and we did trap scab ascospores, but probably had very little green tissue exposed during the wetting period.
This year, we will be tracking and reporting disease update information based on data we are receiving from weather stations placed in Silver Creek Orchards, Pharsalia Road in Tyro, Nelson County, Virginia. Green tip was also reported on Pink Lady apples in that area. There was considerably more wetting in Tyro than at Winchester, easily long enough for scab infection: 26 hr wet at 57-48° F, then 3 hr dry, followed by 7 more hours wet at 34-44°, with a total of 1.72 inch of rain. There was probably enough green tissue exposed during the wetting, so the only question is whether scab ascospores were present and mature for the wetting event. Wherever there was scab present in the orchard or on nearby untended trees in fall 2013, spores were likely mature and available to infect.
Where apples are just beginning to show green-tip, it is definitely time for protective fungicides such as copper or EBDCs; however, if green tissue was exposed during this potential infection event, it would be prudent to include a fungicide with after-infection activity with the protectant if this is the first fungicide application. We have found Vangard (cyprodinil) to be compatible with copper, and effective in such situations. Because of fruit russet concerns, copper materials should not be applied to fresh market fruit after 1/4-inch green-tip stage.
We thank Dr. Mizuho Nita, grape pathologist with Alson H. Smith AREC, Winchester, for procuring funding and placing the weather stations in Tyro. We also thank John Saunders, Silver Creek Orchards, for hosting these weather stations and helping us to install them. As the season progresses, we hope to compare accumulated wetting, temperature, and infection conditions within adjacent grape and apple leaf canopies at three elevations from approximately 944-1462 ft. Dr. Nita's funding came from a VDACS SCRI block grant (Virginia Dept. of Agriculture and Consumer Services, Specialty Crop Research Initiative).
