Tuesday, June 29, 2010

Disease risks from yesterday's rain

Winchester area received precipitations from thunderstorms went through yesterday around noon; however, the rain lasted only 30-40 min and dried up very quickly.  Thus, it was not a significant rain event for any disease development.

Friday, June 25, 2010

Disease risks from yesterday's rain

We had thunderstorms went though yesterday afternoon in Winchester area.  It started around 2 PM, lasted about 20 min, then another one hit around 3:30 PM to 3:50PM.  However; the air was very dry for last few days, and it seems that leaves dried up very quickly after the storm.  Thus, I think it was not good enough for any pathogens to cause disease.

On the other hand, the information is just for our area and your vineyards might have experienced a longer wet event.  Downy mildew pathogen needs only about 90 min to cause infection under the optimal condition (about 68F).  Please check with your local weather service.

In addition, if the night time relative humidity is high, say above 85% or so, the condition will favor the pathogen to produce spores.  Based on the weather record, I see such conditions 4-5 days per week on average in the past few weeks.  In the other word, even though we have not received a rain event that can be an infection event, the environmental conditions are favoring spore production so that once we receive a rain event that gives a long enough wet event, downy mildew can be a problem.  It will really depends on the current downy mildew situation in your vineyards, thus, please spend some time to scout for diseases.

Also, some of varieties are getting close to the stage of bunch closure.  It is earlier than the normal year, but we are having such a hot weather.  This will be a critical time for Botrytis control.  The past study has shown that the number of Botrytis spores in the air tends to be high during veraison; however, if we wait until veraison, the cluster will be tight and a fungicide cannot penetrate into inside of the clusters.  Thus, if your varieties are susceptible to Botrytis, bunch closure is the timing to apply a fungicide against Botrytis.  If needed, you may need to repeat the application at veraison.

We are expecting 20-40% chance of rain during this Sunday and Monday.

Sunday, June 20, 2010

Chance of rain on Tuesday to Thursday

First time in a few weeks, it has been a weekend with no chance of rain.  But there are some chance of rain (~30%) from Tuesday to Thursday.  We are getting close to the end of the critical time for berry infection by black rot, downy mildew, and powdery mildew, thus please be on top of the situation.

Thursday, June 17, 2010

Disease risks from yesterday's rain

Winchester area received an intermittent rain event from 6:00 AM to 4:00PM yesterday.  The relative humidity stayed high (>90%) until 5:00PM.  Thus, this event accounted for approximately 11 hours of wet event with the average temperature of 74F.  It was long and warm enough for Phomopsis, black rot, and Downy mildew infection event.

Thank you very much for those of you who made to yesterday's meeting.  We will have a vineyard meeting tonight at Hiddenbrook Winery from 6:30PM.  Tony and I will be there to discuss about the viticulture and disease management.  If you have a time, please stop by.

Tuesday, June 15, 2010

Disease risks from yesterday's rain and vineyard meetings

Winchester area received a thunderstorm starting around 7:30PM last night.  It lasted only 30 min or so, but the relative humidity stayed high (>90%) until 8:00 AM today.  Thus this event was 12.5 hours of wet event with the average temperature of ~73F.  It was warm and long enough for Phomopsis, black rot, and downy mildew.

We will have a vineyard meeting at Rappahannock cellars tomorrow from 11AM.  Also, we will have another meeting at Hiddenbrook Winery from 6:30PM.  Tony and I will be there to discuss about the viticulture and disease management.  If you have a time, please stop by.

Sunday, June 13, 2010

Note on Revus Top and meeting tomorrow at Democracy Vineyard (Nelson co.)

If you grow Concord and Noiret grape, please be advised that Revus Top (mandipropamid + difenoconazole from Syngenta) may cause phytotoxicity on these variety. The symptoms are light yellow colored scorched (dead) tissue in interveinal area of leaves, and also some deformation of leaves.  Please check this note from Cornell.  We have been testing Revus Top with our Chardonnay in WInchester for two years, but I have not seen any damages on our vines.

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

Disease risks from yesterday's rain

Winchester area received precipitations from thunderstorms yesterday.  It started around 3:30PM and lasted until 7:00PM.  The actual amount of precipitation was not high (0.05 in) compared with other northern VA regions where a severe thunderstorm warning was issued, but since the ending part of the thunderstorm hit during the evening, the relative humidity was high (>90%) until 2 AM or so.  Thus, it accounted for 11.5 hours of wetness with the average temperature of 73F.  It was warm and long enough for Phomopsis, black rot, and downy mildew.

We are still having chances of rain (40-60%) until Monday.

Thursday, June 10, 2010

Disease risks from yesterday's rain

Winchester area received rain from 4:40 AM and a series of rain went through our area until 2:20 PM (0.11 in), the relative humidity was high (>90%) until 4:40 PM, thus, we had about 12 hours of wet event with the average temperature of ~63F.  It was warm and long enough for Phomopsis, Black Rot, and Downy Mildew.

We are also expecting more rain during the weekend.  The chance of precipitation (by thunderstorms) is 30-40% throughout the state during Saturday and Sunday.  I think most of us are still in the critical period for berry infection by black rot, downy mildew, and powdery mildew (bloom to 4-5 weeks after bloom).  Please check your spray program and local weather to make an adjustment, if necessary.

Tuesday, June 8, 2010

Chance of rain from tonight to Wednesday

It seems like there is a chance of rain starting tonight and all day tomorrow.  I was waiting to see if it changes, but now the chance of rain is near 100% for northern VA, and it is lower for the central and southern VA (about 50%).

Monday, June 7, 2010

Disease risks from yesterday's rain and Powdery mildew

Winchester area had thunderstorm yesterday from 12:40 PM to 3 PM (0.27 in), the average temperature was around 72 F.  The relative humidity were low after the storm, thus it accounted for about 3.5 hours of wetness.  Then, another drizzle hit us during 3:20 AM to 4:20 AM (0.02 in), and the RH was high (>90%) until 6:20 AM.  The average temperature during this 3 hour wetness event was 59F.  Since both were relatively short and relatively warm, the risk of downy mildew is the major concern.

As I noted yesterday, we are having hot humid early summer which is a conducive condition for powdery mildew.  Here are today's pictures from our untreated vines that started to show the development of powdery mildew (click the picture to see a larger image).  Please scout your vineyards especially the location where leaves are shaded.  Powdery mildew pathogen prefer to thrive under diffused sunlight conditions.
This is a close-up of powdery mildew pathogen (Erysiphe necator).  The round egg-like structure is a conidia (spore) of this fungus.  Only one per branch (a conidiophore) is shown, but it will form a chain of conidia over time.

Sunday, June 6, 2010

Disease risks from yesterday's rain

Winchester area received isolated rain events yesterday (6/5/10).  The intensity of the rain varied by area, thus, I'm just giving a general idea.  Based on the record, we had rains between 1-3PM and 7-10PM; however, the events were composed of a series of very light rains (less than 0.01 inches), the relative humidity was low (70-80% range), and temperature was high (mid-80's to mid-70's).  Thus, even though we could have a chance of a long wetness period, my guess is that leaves were not wet long enough for many fungal pathogens (Phomopsis, black rot, and downy mildew) to take advantage.  On the other hand, this humid hot cloudy condition may be ideal for powdery mildew development. 

We are still having a chance of rain this afternoon.  It seems like northern VA will receive some thunderstorms.

Friday, June 4, 2010

Thunderstorms forecasted for this weekend

The situation has not changed yet.  We are still expecting some thunderstorms in the state. The chance of precipitation is somewhere between 30-50% throughout the weekend.

Winchester area received about 0.02 inch of rain yesterday afternoon.  It only lasted about 1 hour, thus it was not a critical disease event. 

Since most of our berries are still in the critical period for downy mildew, black rot, and powdery mildew.  As I have been discussing in various vineyard meetings, black rot requires a certain length of wetness in order to have an infection.  With the optimal condition (~75F), it requires 6 hours.  Downy mildew takes less, about 90 min.  Powdery mildew does not require rain.  Thus, with thunderstorms, it is important to know how long it lasted.  If it was less than 90 min, you probably do not need to worry about risk of diseases.  If it lasted longer than 90 min, then downy mildew comes into play.  If it started late in the evening and the relative humidity is high (> 90%) for more than 6 hours, then depends on the temperature, black rot could have an infection.  For the details on infection conditions, please refer to my vineyard notes.

Wednesday, June 2, 2010

More forecasted rains during this week + mealybugs

We did not receive any considerable rain during the weekend.  At this point, I am not certain what to believe.  I think the atmosphere is unstable and conducive to create thunderstorms.  We are expecting 30-40% chance of thunderstorm from tomorrow to Sunday.

I have seen a small outbreak of mealybugs in our field (please click the picture to see a larger image).  It is a good news for me because I was looking for them, but as you may know, this insect can vector a virus that can cause grape leaf roll disease.  Thus, if you have seen these bugs, please contact me so that I can visit your place to collect samples.  It is very important for us to know which species are present in VA in order to understand the risk of leaf roll spread.  It is a part of on-going leaf roll project and we need more information on this important pest.  Mealybugs are about less than 1/8 of an inch in length and often covered by white hair-like tissues.  Often time, you will find mealybugs underneath the leaf or within the bark.  They seems to like shade and often associated with ants which like to feed on the honeydew that is secreted by mealybugs.