Monday, April 25, 2011
Disease risks from a wet weekend
Then, we had rain events on 9:20PM on 23rd, 3:40 PM and 10:20PM on 24th. All of them are in higher temperature ranges (mid to high 60's), but lengths of wetness were short (2-3 hours). The only disease that can cause under these conditions are downy mildew.
The optimum temperature range for downy mildew infection is mid-60's to mid-70's, and under that condition, it takes only 90 min or so to cause infection. On the other hand, it is relatively early in the season, and the overall temperature profile in the past few weeks may not favor the development of downy mildew. It probably won't be the case for the most of us because 2010 was a very dry season; however, if you had a history of downy mildew outbreak in last few years, you may want to monitor your vines closely in the next few weeks.