After delayed bud development through the last two weeks of March, we saw our first green tip on Red Delicious apples at our our AREC in Winchester last week Mar 27. Apple scab ascospores were released, and we recorded 49 hr of wetting at 35-47°
F with 0.5 in. of rainfall from Mar 27-29. So this was an apple scab infection period where there was enough green tissue exposed during the wetting. Over the weekend, bud development advanced as far as 1/4-in. greentip on Red Delicious by Apr 2, as shown below. Last week's wetting conditions varied somewhat east of the Blue Ridge, but it is likely that scab infection could have occurred wherever the bud stage was more advanced, from Rappahannock southward to central Virginia.
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| Red Delicious apple buds at Winchester April 2. |
Overwintering buds infected with powdery mildew were evident at Winchester by Apr 2, and it is expected that mildew spores will be released as leaf tissue in infected buds expands and the leaves unroll.
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| Idared apple bud infected with the powdery mildew fungus (right), compared with a healthy bud (left), Apr 2. Note weaker growth and reddish appearance of emerging tissues. There would have been no indication that this was an infected bud prior to budbreak. |
Powdery mildew can infect developing blossoms at pink stage and cause the mildew-russet shown below. Mildew infection occurs with dry weather during temperatures above 53° F.
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| Net-like russet of Jonathan apple caused by mildew infection at pink stage. |
