Disease risks from 6/13

A storm went through our area and resulted in several wetness events.  The longest one was about 11 hours of wetness with an average temperature of 68F.  It was a disease infection event for black rot, Phomopsis, downy mildew, and Botrytis.

Disease risks from 6/6-6/8 rains

A series of rain event started around 9:30 AM on June 6th, and continued on until about 2AM on June 8th at Winchester.  Thus we had a wetness event for about 40 hours with an average temperature of lower 60F (~63F).  It was long and warm enough for Phomopsis, black rot, downy mildew, and Botrytis. 

If you are planning for fungicide application to reduce the risk of on-going infection of downy mildew or black rot, please refer to this post, or PMG, or my workbook (PMG and workbook are listed under "Resources").  Looks like chances of rain remain high for next few days across the state.

FYI: Because we have seen downy mildew in our vineyard since last week, we applied Prophyt (a phoshite material) and Ranman (cyazofamid) yesterday morning.  A phosphite material and cyazofamid has a kick-back activity and a protective activity against downy mildew, respectively.  (Note: We did not apply a material for black rot, because it may interfere with some of our experiments.) 

Disease risks from yesterday's rain event

Winchester area received a series of thunderstorms from 3:00 PM yesterday, and relative humidity remained high (>90%) until 9:00 AM this morning.  Thus we had a wetness event of 18 hours with an average temperature of 66-67F.  It was warm and long enough for Phomopsis, black rot, downy mildew, and Botrytis infection.

Bloom 2013

-->

I just visited another vineyard down in the south where Norton vines were in full bloom, and when I came back, our Chardonnay vines were in trace-bloom.  As we discussed at this year’s VVA meeting, bloom is a very critical time for disease management.  Downy mildew, powdery mildew, and black rot tend to show up around this time of the season, and berries will be susceptible to these diseases until 4-6 weeks after bloom.  In addition, Botrytis, ripe rot, and bitter rot can cause infection on flowers.  Management of Botrytis, ripe rot, and bitter rot at bloom time can be important because these fungi can infect flower, and come back later when berries are maturing. 

As you know, development of a disease depends on so many factors such as availability of inoculum (~ disease history), past and future weather conditions, variety, canopy management, etc., thus, I will not go in to details.  However, based on the past few weeks of rain events and a trend of warm humid nights we observed, as well as a forecast of thunderstorms during this weekend, it would not be a bad idea to think about downy mildew, since these humid nights can promote spore production of the downy mildew pathogen.   Phosphite (= Phosphorous acid) or Metalaxyl (Ridomil) product have a kick-back activity against downy mildew.  If your vineyards have a history of black rot, then a DMI material may need to be considered because they have a kick-back activity against black rot.  (Of course, since I made these statements, we may not see many rain evens, and may end up not having much of downy or black rot.  We will see...) Please refer to either Pest Management Guide or my Workbook for more detailed information on fungicide selection for each disease.

For Botrytis, ripe rot, and bitter rot, please keep in your mind that early season powdery mildew management can become important to prevent these diseases.  These pathogens are very good at infecting through wounds; thus, scars, which will turn into opening of the skin, caused by powdery mildew infection on young berries can be the ideal targets for them.

Disease risks from last few days

In Winchester area, rains from May 22-23 resulted in ~19 hours of wetness with an average temperature in lower 60's. We had 5-6 hours of dry period, then another rains went through the area, starting around 5PM last night. Relative humidity remained high (>90%) until around 5AM this morning, thus it was about 12 hours of wetness. Average temperature was again in low 60F. Both were infection events for Phomopsis and black rot. A total precipitation of the last three days was about 0.7 inches. Also, in the last few days, night time temperatures were warm (in 60's) and relative humidity were high, thus, these could be downy mildew sporulation events as well.

Disease risk from May20th

We did not receive afternoon rains at Winchester yesterday. We were hoping for it because we are planing a new vineyard... However, we received a short rain around midnight yesterday (5/20/13). It was followed by fog, and relative humidity stayed high (>90%) for almost 9 hours with average temperature in low 60's. It was an infection event for Phomopsis and black rot.

Frost injury (and disease risks from this weekend)

Damages from Monday's frost event showed up a few days after.  About 5-10% of shoots (or leaves) on our Merlot vines which is located near the bottom of a hill showed symptoms.  Some are simply become necrotic, and others are showing mosaic symptoms.

Also, although there were drizzles here and there, rains from this weekend were not long enough to be disease events at our location.  However, relative humidity was high (near 100%) throughout the last night.  Such a condition can promote sporulation of downy mildew.