At our AREC we had green tip on Red Delicious (shown above) and other apples March 16 and about 1/4-inch green by March 17. 55 hours of wetting, with discharge of apple scab ascospores, had occurred from March 13-15. This was more than three times the length of wetting required for scab infection where green tissue was exposed, but our buds had not advanced to that stage by that time.
Scab infection was likely in areas where buds were more advanced to the green-tip stage. In Tyro, Virginia, 51 hours of wetting was recorded at temperatures that were about 5 degrees warmer than at Winchester, resulting in more than four times the length of wetting required for scab infection. Apple scab ascospore maturity at green-tip stage is normal and should be expected except in years when buds advance rapidly without any moisture to mature the spores.
Powdery mildew spore production is advanced compared to most years. Typically, buds infected with overwintering mildew are somewhat delayed compared to their healthy counterparts. However, I was surprised to see mildew-infected buds as advanced as healthy ones (upper right, below), and they had an abundance of conidia (below). In contrast to wetting conditions needed for scab infection, powdery mildew is able to infect on dry days with temperatures above 53 degrees F.
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| Mildew infected Idared bud, upper right. |
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| Mildew conidia on Idared. Winchester, March 17, 2016 |
Cedar-apple rust galls are also ready to produce infective basidiospores with the next warm wetting period, so protective apple fungicides should now be included for mildew and rusts as well as for scab.
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| Cedar-apple rust gall ready to produce spores March 16. Virginia Tech AREC, Winchester. |
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| Redhaven peach bud development at Virginia Tech AREC, Winchester, March 17, 2016. |
Peach buds (above) were more advanced than apples, and unprotected buds would have been readily susceptible to leaf curl infection with wetting March 13-15. Because spores of the leaf curl fungus are carried on the surface of the tree from the fall to spring, fungicides applied in the fall or during the winter give good protection from leaf curl. Fall applications help to avoid the spring rush to spray before pruning brush is removed from the orchard.
