debor039

It finally stopped raining, but we (Winchester area) are having an on-going wet event since 10/9/13.  I counted >108 hours of wetness with an average temperature of 54F (ranging from 48F to 60F).  It has been a long enough for Botrytis, and although the temperature was bit low, downy mildew probably had some chances as well. Here is a list of things to be considered: 1) Time to harvest (if you are picking in a few days, I do not see the benefit of spraying now) 2) Current Botrytis situation in your vineyards 3) Variety (red with loose cluster ~ lower Botrytis risk) 4) Canopy management (Open fruiting zone is always helpful!) 5) Birds/insect damages (more damages, higher the Botrytis risk) 6) Fungicide effect on wine quality As I mentioned earlier this week, we had Botrytis risk event on last Monday; however, it had been dry for several weeks until that rain.  Thus, the Monday's risk might not have resulted in many infections.  On the other hand, Botrytis spores ar...

Rain on this Monday resulted in 10 hours of wetness with an average temperature of 62F.  It was warm and long enough for both downy mildew and Botrytis.  Once again, downy mildew risk is for leaves only.  Risk of Botrytis depends on your variety, cluster architecture, and canopy management too.  Most of varieties still hanging are red (with some exceptions, of course), which has lower risk of Botrytis.  Also, if you have an open canopy, the risk are lower too.

Since 9/2 or so, we are observing dew events that were wet enough to make our leaf wetness sensor wet almost every night.  Since our sensors were located about the same height as the lower part of the canopy, leaves were probably wet as well.  Each events were about 6-9 hours.  Most of time, temperature was low (in 50F), but sometimes were in lower 60F.  What this condition promote can be downy mildew.  They tend to sporulate under dark condition, and since their spores can swim, these dews probably are enough for them to infect new tissues.  Due to low Brix, many people are tying to hang their berries longer this year.  Please make sure to have some protection on your foliage so that it can help maturation of berries (+ store carbohydrate for the winter!).  If you are concerned about potential effect of spray materials on wine quality, you can aim your sprayer nozzles to upper part of the canopy so that fungicides won't hit the berries.

A rain event followed by high relative humidity (+28 hours of wetness in high 60F) created disease risk event for downy mildew and Botrytis on 8/28-29.

A wetness event recorded yesterday was infection event for Botrytis and Downy mildew.  Refer to yesterday's post on spray choices.  Please make sure to alternate mode of actions to reduce the risk of fungicide resistance development.

Continuous rain and high relative humidity caused Botrytis and downy mildew infection risk events on the 14th, 17th, and 20th. At this point of the season, a phosphite (aka phosphonate or phosphorous acid) material would be the best choice for downy mildew.  You may want to mix it will captan to have added efficacy. (Note: captan has 0-day PHI, but some winemaker prefer not having captan close (~3 weeks) to the harvest.)  The other potential mixing partner would be Ranman (note PHI = 30 days), Forum (PHI=28 days), or Revus (PHI=14 days).  Ranman should have some kick-back activity, and both Forum and Revus have a protective activity. As for Botrytis, we only have protective action materials, thus, please make sure to have a good coverage on your clusters.  Moreover, please make sure to rotate mode of action since this pathogen is known to develop resistance to fungicide rapidly.

Botrytis risk has been high from 8/9 to 8/13 due to frequent rain event.  This also means that downy mildew risk is high too. (I am at a conference, so, I cannot provide detailed data.  I will update it once I am back this weekend.)