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Notes on Phomopsis

 It seems that we will observe sunny days with 60-70F for next few days.  Hopefully, the night time temperature won't drop too low.  Our Chardonnay vines are showing a little bit of deformation on leaves, probably due to the low temperature during the night.  Unless we will have more cold nights, it should overcome the stress.

 Most of our early varieties (e.g., Chardonnay, Merlot) are in this stage (1-2 inches long).  Please note that the flower cluster is already exposed at this point.  Fortunately, we are not expecting a rain event soon, but at this point, the shoot is susceptible to Phomopsis.  If the fungus successfully infects rachis tissue, it may cause a premature fruit drop later in the season.

 The picture on the right was taken last year.  As you can see, a part of rachis became necrotic due to Phomopsis infection, and berries were dropped because the rachis is dead.
 The fungus survives in canes and trunks that are infected in previous years, and during the spring it will produce spores that are splashed by rain onto new tissues.  Thus, it is important to protect young tissues when it is close to the older canes and trunks (i.e., now!).

 It requires rain event to cause infection, thus you need to monitor your local weather forecast.  If a rain is coming into the picture, mancozeb (Penncozeb, Dithane, etc.) is an effective protective material against Phomopsis.  At this point, no materials are effective after the infection.

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