Thursday, August 26, 2010

Disease risks from this week's rain

I was out to the eastern shore for an extension trip and missed the rain event!  During 8/23-24, Winchester area received around 0.29 inches of rain.  The event started from around 5PM on 23rd and ended around 4:30 AM on 24th.  The RH was above 90% until noon or so.  Thus, this event accounted for 20hr of wet event with an average temperature around 68F.  It was warm and long enough for both downy mildew and Botrytis.

So far, no rain is in this weekend's forecast. 

Friday, August 20, 2010

Disease risks from yesterday's rain and more rains in the forecast

Winchester area received 0.42 inches of rain during August 18-19, resulting in 26 hours at an average of 68F. It was long and warm enough for both downy mildew and Botrytis.  Once again, please scout for downy and powdery just in case.

Also, we are expecting more rains during this weekend (30-50%).

Monday, August 16, 2010

Disease risks from weekend's rain

Finally!  Winchester area had decent rain events over the weekend.  The rain event started from 7:40PM on Thursday (we missed the one earlier that day, although other northern VA area received thunderstorms), and a series of rain went pass throughout last Friday.  The relative humidity was above 90% until 8:20PM on Friday.  It resulted in almost 25 hours of wet event with an average temperature of ~74F.  It was a long and warm enough for downy mildew and Botrytis.  Then we had several rain events on Saturday and Sunday.  None of them are very long, but long enough for downy mildew to cause infection.

Once again, we had a dry summer and the threat from downy mildew may or may not be the primary concern.  But if you still have a few more weeks to go until the harvest, please keep your eyes on younger foliages (typically you find them on the upper part of the canopy) for the sign of downy mildew.  It can go from a trace level to an outbreak in a short time, and heavy infection can cause defoliation on leaves.  If you knew you have some downy prior to this series of rain over the weekend and your leaves are not protected, you may want to consider Phosphorous acid products such as Prophyt which should give you a good curative and protective activity against downy mildew (+ short PHI).

Also, there are chances of rain (30-70%) on this Wednesday and Thursday.

Sunday, August 8, 2010

Disease risks of last week

Winchester area experienced much needed rain events during last week (8/3 to 8/4 and 8/5).  [note: I'm at a meeting right now and I didn't have a time to update the information before I took off to this meeting.]

Light rains went through during evening of 8/3 and then after midnight/early morning (1:20AM) in  (8/4), then a thunderstorm hit in the afternoon.  The first series of rains were short and low in the amount of precipitation, but since it occurred at night, the relative humidity stayed high (>90%) until 9:30 AM or so, resulting in 8 hour of wetness with an average temperature of 78F.  The thunderstorm was not as big as we hoped for (it became more severe and brought more rain after it passed our area), and things dried up within an hour.  The midnight rain event was warm and long enough for Downy mildew and Botrytis development.

Then another series of thunderstorm hit our area on 8/5.  As with any thunderstorms, it was sporadic and some area received more than others even within the same area.  It started around 1PM and several lines of rain passed until around 6PM, dropping ~0.38 inches.  However, the air was dry in between rains and after the rain, thus, it probably only accounted as Downy mildew event.

Also we are having several humid nights during last 10 days or so.  This conditions favors spore production of downy mildew.  As I noted in the previous post, many of us had such a dry weather this summer and downy may not be the primary concern; however, we are having weather events that favors infection and spore production.  Please scout for downy by looking at young leaves and if needed, react to the situation.

As noted earlier, I'm at a meeting until next Wednesday (8/11).  The best way to contact me is email.  We don't have rain in the forecast until Thursday.

Monday, August 2, 2010

Disease risks from yesterday's rain and some rains in the forecast

Well, I almost missed it, but we (Winchester area) had a short rain event started from Saturday night around 11:20 PM, lasted until 12:00 AM or so Sunday.  Although it was not a major rain event, it started late at night and the relative humidity was high (>90%) until 8:20AM (=9 hours of wetness event), with an average temperature of around 68F.  Thus, it was warm and long enough for both downy mildew and Botrytis.  Since it has been so dry that it may not have much impact, but it is worth noting.

We are expecting some chance of rain (30-40%) from tomorrow to Friday.  I'm not sure how much of these chances become real, but we need some rain...

Our meeting is coming this Wednesday!  I hope you can make it.