Monday, July 26, 2010

Disease risks from yesterday's rain + meeting info.

Boy, it was some strong wind we experienced during a thunderstorm yesterday!  I saw a few trees fell down in the downtown Winchester.  That storm brought about 0.38 inches of water, the rain lasted about 80 min, then everything dried up very quickly.  This rain was a borderline case for downy mildew infection event.  This fungus (or oomycete, if you wan to be precise), can infect grape tissues in 90 min.  At the same time, it has been very dry for us, so, the overall risk may be low. 

Even though the critical time has passed for berry infection of downy and powdery mildew, you need to maintain your leaves reasonably healthy for your crop and also for next year (accumulation of carbohydrate to trunks).  Please keep scouting for powdery and downy by checking younger susceptible leaves on the top of canopies.

The weather forecast is showing a chance of rain tomorrow and Thursday.  I think we need little more rain for our vines...

  • I will be out for a meeting until this Thursday.  If you need to contact me, email will be the best way.   I will try to update this page, if I have a good web access.  
  • Also, we will have a vineyard meeting at out Winchester AREC on August 4th from 11AM.  If you have time, please stop by.  You get to see vines full of powdery mildew!

Sunday, July 25, 2010

Chance of rain during this weekend.

There is a chance of rain this afternoon (50%).  More importantly, there is a heat advisory issued throughout northern VA.  Dulles airport recorded historical high (99F) yesterday.  Please be careful if you are working outside. 

We only received less than one hour of rain during early part of the week.  It was a little sprinkles here and there and not a disease event.  (I was so disappointed that I forgot to post on here.)

Sunday, July 18, 2010

Chance of rain tomorrow and Tuesday (7/19-20/2010)

There are some chance of rain (30-40%) predicted tomorrow and then Tuesday.  At this point the main concern will be downy mildew on foliages and also late season rots.

Wednesday, July 14, 2010

Disease risks from yesterday's rain

Finally, we received a decent amount of precipitation.  Although the central VA received a much needed rain on Monday, Winchester and surrounding area received only about 0.02 inches of rain.  Then on Tuesday, Winchester area received a series of thunderstorms from 5 PM until little after midnight on Wednesday (~ 1 inch).  The relative humidity stayed high (>90%) until 8 AM this morning.  It accounted for an estimated 15 hours of wetness with an average temperature of 77F.  It was long and warm enough for infection process of downy mildew, black rot, Botrytis, and Phomopsis.

We are also expecting around 30% chance of rain on both Friday and Saturday.

Sunday, July 11, 2010

Disease risks from yesterday's rain and vineyard meetings

We received a series of thunderstorms from Friday night to Saturday morning.  At Winchester, the rain started around 8:00 PM Friday night and lasted until around 9:40 AM Saturday morning.  Soon after the last drops of rain, the sun came through the clouds and things were dried up again. Thus, it accounted for about 13:40 hours of wetness with an average temperature of about 75F.  It was warm and long enough for downy mildew, black rot, and Phomopsis.

We will have a vineyard meeting tomorrow from 11 AM at Blenheim Vineyards.  If you have a time, please stop by.

Friday, July 9, 2010

Late seson rots management tips

There are chance of rain (40-70% across the state) predicted during tonight to Saturday. We really need some rains, so, I'm hoping that we all will get a decent rain.  We will see...

Now probably many of you are considering disease management at or after veraison.  One of diseases you may be concerned at this time of the season are late season rots (sour rot and/or Botrytis gray mold, caused by Aspergillus niger, Alternaria tenuis, Botrytis cinerea, Cladosporium herbarum, Rhizopus arrhizus, Penicillium sp., and others).  These late season rots come in when fruit sugar content accumulates around 8%, and often times, white varieties with tight clusters such as Vignoles and Chardonnay, tend to get this disease more than other varieties because of the structure of the cluster which can hold water inside and also because of the fair skin.

The sour rot pathogens, including Botrytis, are opportunistic in nature, and the damage and the risk will increase if Botytis rot is involved.  Typically, Botrytis management needs to be done at early in the season.
  • For example, at bloom powdery mildew management is a key because once these young berries are infected by powdery, even to the point that you don't really see symptoms, it will damage grape berry skin enough to cause wounds later in the season to invite these rot pathogens in. 
  • Botrytis can infect flower part as well, thus, if it often recommended using Botrytis specific materials at bloom. 
  • With the same logic, the management of grape berry moth, wasps, and birds can lower the risk of infection.
The cultural practice plays a very important role on the late season rots management.
  • Proper shoot positioning and canopy management will decrease the risk of Botrytis infection by lower humidity of the fruiting zone.
  • Leaf removal around fruit set has been recommended for some varieties to increase the air movement around clusters.
  • Leaf removal around veraison will help thickening of skins.
    • Thus, some people perform leaf removal around fruit set to open up the eastern-side of canopy and do it again around veraison to open the western-side.
    • However, it may also increase the risk of sun damages on the berries, thus, check to see if the leaf removal is a good tactic for your varieties.
  • Bunch thinning can also be done at veraison to reduce the risk of having berries with high sugar lying around the vineyard to invite insect pests.
There are only a few options with the chemical management against late season rots, and none of them will provide a complete control.
  • Botrytis materials such as Rovral, Elevate, Pristine, etc., and captan is often recommended.
  • In addition, the use of a copper fungicide (Bordeaux mixture, etc.) has been recommended as a tank mix with a Botrytis material because in addition to its fungicidal activities, some study showed that copper helps grape berry skins to become thick.

Tuesday, July 6, 2010

Hot weather and powdery mildew

As you know, we are expecting to have a high temperature for next few days.  Please protect yourself from heat related illnesses.  

Having this much of heat is not really a fun, but there is a good aspect as well.  Powdery mildew pathogen cannot survive very well under high temperature.  At 33C (92F) or more, this fungus will suffer, and colonies can get killed.  If there is an extensive exposure to the sunlight and high temperature (as we have right now), they will have a difficulty surviving.  A study has shown that the fungus colonies will be completely killed after 12 hours at 35C.  Thus, this heat wave should reduce the risk of disease development, especially if you had a good canopy management.

Saturday, July 3, 2010

Happy 4th!!

I wish you all a happy 4th of July!!

We haven't have rains lately = no risks for downy mildew nor black rot.  If you are happened to be in your vineyards, please scout for powdery mildew.