Tuesday, June 24, 2014

Dews and humidity in the past few days

We have not received precipitation since the 21st, but every night since then has been humid.  Dews that formed 3-4 AM stayed until 9-10 AM in some days.  Once again, these conditions favors downy mildew spore development. 

If your vines are covered with a previous application, you do not need to worry about it, but if not (say, the last application was more than 10 days ago, or you had more than 1.5-2 inches of rain since the last application), then you may want to consider a protective application before next thunderstorm hits, which may happen in the next few days.  We are almost through with the critical period, though!

Sunday, June 22, 2014

Yet another rain events on June 21-22

Winchester area was rained out pretty much whole day yesterday, resulted in two wetness events, one with ~16 h of wetness with low 60F, and another one with ~7 hours of wetness with high 50F.  These resulted in infection risk event for black rot, downy mildew, Botrytis and Phomopsis.  Once again, please try to be on top of the situation while we are in the critical period for cluster infection.

Tuesday, June 17, 2014

Disease risks from last night

A thundershower hit Winchester area around 6PM last night, resulted in 16 hours of wetness with lower 60F in average temperature.  It was disease risk event for black rot, downy mildew, Phomopsis, and Botrytis.

As with last few rains, it resulted in a warm and humid night that helps downy mildew to produce spores.  Many of us are still in critical period for cluster infection, and this is the time of the year to be on top of the game.  Please refer to previous few posts about spray ideas.

Friday, June 13, 2014

Disease risks from last few days, and a plan for next spray

Boy, what a week!
Winchester area received about 17 hours of wetness with average temperature of 20 C (68F) on the 11th, 14 hours of wetness with average temperature of 22 C (72F) on the 12th, and right now on-going wetness with 17hour + with an average temperature of low 20C (68F).

These events are warm and long enough for downy mildew, Botrytis, Black rot and Phomopsis.  On top of that because of evening rain events, night time conditions have been favoring downy mildew development.  Our main concern is downy and black rot since our clusters are currently in critical period.  These berries are susceptible to the infection by these pathogens.

It looks like the weekend weather is promising, and a 10-day forecast is calling for a chance of rain again on Tuesday... what can we do?

For our vines, the last application was made 10 days ago, and we received a total of 1.47 inches of rain at the site.  Last application was mancozeb + sulfur + Phosphite (Prophyt, Phostorl, etc.) + Rally. Our Chardonnay is on its 6th leaf, clusters are about BB side, and the site is not good.  We have chronic issues with powdery and downy.

Plan A) mancozeb + sulfur + Phosphite + Rally. 
  • This is the second Rally (DMI) application for the season, but since they are BB-size, I am hoping that this will cover most of the critical period.  Knowing that we had 1.5 inches of rain since the last spray, I may want to be safe.  If I decided to do it, this will be our last Rally application for the season.
Plan B) mancozeb + sulfur + Phosphite + Pristine
  • We have not used Pristine this season.  I know that our downy mildew populations are resistant to QoI (one of components in Pristine), but considering potential black rot infection, this would make a good rotation partner.  
  • Please note that although a QoI has a kick-back activity against black rot, Rally has a better efficacy based on a study.
Plan C) Ridomil Gold MZ + mancozeb (with rate adjustment) + sulfur + Rally (or Pristine)
  • With all the rains we received, this may be the time to consider Ridomil.  I tend to rely on a phosphite more because of the resistance issues (relatively speaking phosphite has a lower risk), but Ridomil tends to have better kick-back activities, and it is always nice to mix things up.
  • Yes, you can mix Ridomil and a phosphite too!  I typically do not recommend it, simply because it tends to become an expensive application.   I rather hit it with a phoshite first and then hit it again with Ridomil.
Please note that these are just examples, and the actual decision needs to be based on what and when you have sprayed in the past, variety, site, amount of rain you received, etc., etc.  For example, I am not considering Botrytis specific chemicals because Chardonnay passed its flowering time, but if I need to make a plan for Cab sauv. for this week, I will add something like Vanguard.

Also don't forget to check for grape berry moth!  I have heard from several people about webbing in clusters.

Tuesday, June 10, 2014

Disease risk event from yesterday

The rain event started on the night of the 8th resulted in about 14 hours of wetness with about 65F in average temperature.  This was infection risk event for downy mildew, Botrytis, Black rot, and Phomopsis.  Also, in the last two nights, the evening thunder storms brought up night time relative humidity, thus, we should keep watching out for downy mildew development.

Monday, June 2, 2014

Seasonal disease management reminders at bloom time

Many people in northern VA are about to see blooms (our Chardonnay vines are trace bloom as of June 2nd, the one on the picture is one of the few with many open flowers), and I am sure rest of regions are going through bloom by now.  Therefore, many of us are in the critical time for cluster infections by downy mildew, powdery mildew, and black rot.  Bloom time is also critical period to prevent Botrytis, ripe rot and Bitter rot, because pathogens of these diseases can infect flower parts and come back later.

We do have materials with kick-back activities against downy (Ridomil products, Phosphonates, etc.) and black rot (myclobutanil, etc.), but infection on flowers and young fruits can happen very fast.  Unless we have a very dry season, this is the time where you have to be proactive.  Thus, what I recommend often is use of protectant materials to protect tissues for 4-6 weeks for V. vinifera varieties, and 3-4 weeks for V. labrusca varieties, which should translate into 3-4 sprays for vinifera, and 2-3 sprays for labrusca.  Please make sure to rotate mode of action groups.

Here is an example from our experimental vineyards.
1)   At bloom: mancozeb + sulfur + myclobutanil or another DMI + Vangard (+ phosphonate, if it rains a lot)
2)   First cover: mancozeb + sulfur + Quintec (+ phosohonate, if it rains a lot)
3)   Second cover: mancozeb + sulfur + myclobutanil or another DMI (+ phosohonate, if it rains a lot)
4)   Third cover: captan + sulfur + Quintec (if needed, if I do not see any evidence of powdery mildew, I may omit Quintec from this spray) (+ phosohonate, if it rains a lot)

The spray interval depends on the weather conditions; so, I cannot give you a specific number.  However, in general, I would aim for shorter intervals for sprays #1, #2, and #3 (7 to 12 days), but I may relax a bit for #3 and #4 (10 to 14 days), if weather condition does not favor downy or black rot.   

Please note:
  • I am saving my DMI (Rally, Elite, Mettle, Revus Top, Luna Experience, etc, etc.) and Quintec (or Vivando, Torino, or any other new powdery material) usages for the critical period, thus this is the only time we spray these materials. 
  • I would like to use a mancozeb product around bloom because it has activities against multiple pathogens including pathogens for black rot and ripe rot.   
    • Captan is not as effective as mancozeb when it comes to black rot management.   
  • The third cover may become too close to the 66-day PHI, so, you need to be careful with the usage of a mancozeb product.

Of course the example given above is just one example, and there are many other options.  For example, there are many new materials became available for powdery mildew management in recent years.  Thus, as usual, please refer to our PMG for more details.