Monday, March 29, 2010

Update 3/29/10

Apple scab:
Bud stage on different cultivars now ranges from green tip to tight cluster. Wetting from 2 PM March 28-1 PM March 29 resulted in our first scab infection. Assuming that few orchards have had any protectant fungicide (copper, EBDC, etc.) applied before the recent rains, it is advised that a fungicide mixture including some back action on scab be applied as soon as it is suitable for spraying. Where the scab fungus has become resistant to SI fungicides (Rally, Rubigan, etc.), after-infection fungicide options include a strobilurin (Flint, Sovran) or an AP (Vangard, Scala) and these should be combined with an EBDC (mancozeb). For processing varieties, where there is less concern about fruit russet problems, there may be interest in applying copper as a protectant for fire blight and scab. We have tested the tank-mix combination of Vangard + copper and found that it is suitable to add Vangard to copper for post-infection control of scab. Be aware that copper does not give post-infection control of scab, and the Vangard + copper tank-mix will not control rusts or mildew.

Apple powdery mildew:
Predicted warm and dry weather later this week will bring rapid bud advancement and early secondary powdery mildew infection of leaves and blossoms.  The image at the right shows chains of  powdery mildew conidia emerging from an infected Idared flower sepal 3/31/10.

Check the rust gall inoculum in your area; cedar-apple rust and quince rust spores will likely be released with the next warm rain.

Saturday, March 27, 2010

It's a new season!

Late winter snow cover aided overwintering of apple scab ascospores. We had green tip showing on Idared apples by March 19. Scab spores were first trapped with rains last Monday morning, March 22. By our AREC records, the extended wetting from 8 PM March 25 to 11 AM March 26 was not quite long enough for scab infection, but showers in the area were variable and one more hour’s wetting would have resulted in a scab infection period.

Peach leaf curl spores overwinter all over the surface of the tree and, if not controlled by a dormant fungicide, typically infect with the wetting periods soon after bud swell. This would have occurred with rains March 25-26.