|Ginger Gold apple bud stage, April 16, 2014|
As shown above, apples at our AREC were mostly in open cluster bud stage Wednesday morning, April 16.
Scab and rust infection period: We had about 13 hr wetting in the 59-64° range Apr 14-15, followed by another 10 hr wet as the temperature dropped from 55 to 38. This was plenty enough for scab, quince rust and cedar-apple and infection.
As usual, we saw powdery mildew spores emerging from tight cluster stage buds last week, and mildew infection would have occurred with dry weather April 9-10 and 13-14, so we should now be spraying apples for scab, the rusts and mildew.
After-infection control of rusts: Quince rust and cedar-apple rust spores were released and likely found a susceptible target in apple blossoms at open cluster. It is best to include an SI fungicide for after-infection control of rusts, especially quince rust, considering yesterday’s warm infection period. If an EBDC fungicide had been applied just before the rain, it may have weathered through with less than an inch of rain, but where rainfall was more an inch or the most recent fungicide application was more than a week earlier, applied more than a week ago, it is best to follow-up with a supplemental SI fungicide for after-infection control of rusts.
Fire blight?: The warm temperatures over the weekend to Apr 15 might have favored fire blight Apr 14-15 if bloom opened April 11-13, but fire blight infection was not likely where bloom first opened during the day April 14 or 15. Now it looks like it will remain relatively cool into next week, but with warmer temperatures and more bloom expected by the middle of next week. Of course the fire blight threat can change quickly if the temperatures are warmer than predicted.
TYRO, VA: Similar apple disease scenarios were expected for central Virginia, where the bud stage is more advanced with bloom open last week, temperatures generally several degrees warmer and rainfall reported to be as much as 2.4 inch.