Tuesday, June 28, 2016

Another reminder on seasonal diseases

Photo: we have started to see powdery mildew on clusters. I hope you are not!

Looks like series of thunderstorms are hitting various part of the state this week. Just a reminder that due to April frost events, some of us experienced extended bloom. This not only means potential lag in harvest time for these late clusters, but also, an extended critical period for seasonal diseases. Grape clusters are susceptible to black rot, downy mildew, and powdery mildew from bloom to 4-5 weeks after bloom (3-4 weeks for American grapes). Thus, this is the time I want you to be on top of the game (i.e., nice coverage, 7-10 days interval, good selection of fungicides to be applied).

Many growers told me that if they are clean around the Fourth of July weekend, you don't expect outbreak of black rot, downy mildew, and powdery mildew. I generally agree with their assessments since in many years, bloom happens late May or early June. However, this year, bloom started the first week of June, but I saw delayed bloom until the middle of June, thus, I will keep my schedule relatively tight until early to mid-July (i.e., rather than the Fourth of July weekend, I would aim for the next weekend). Since we are having several rain events in the past few days, I would watch the forecast carefully, and prepare for good protection against, downy (e.g., Revus (Top), Zampro, Ranman, mancozeb, Phosphite, etc), black rot (DMI (Rally, Revus Top, Luna Experience, etc), mancozeb, QoI (Pristine, Abound, etc)), and powdery mildew (Vivando, Luna Experience, Quintec, Tanos, sulfur, etc). Please note that some of mixed materials may have efficacy on multiple diseases.

Also, we will have a vineyard meeting at Arterra Wines in Delaplane, VA from 11:00 AM tomorrow. I hope to see you there!

Tuesday, June 21, 2016

Handout from last week's meeting + we are still in the critical period!

Here's my handout from last week's meeting at Stone Tower Winery. Thanks for those who attended the meeting!

It looks like we may have rains here and there this week. Since we have not had significant rains in the past week or so, the risks of downy maybe low, but most of us are still in the middle of critical period for cluster protection. Please refer to my at bloom post for more details on disease management tips for this time of the year. Once we pass this period, we can relax a bit, in terms of fungal disease management.

Monday, June 6, 2016

What to do when you receive a lots of rain after fungicide application?

At Winchester area, we ended up having a pretty good weekend. There were several periods with rain, but it was not as extensive as the forecast. We received about an inch total over 2-3 days. However, it looks like the central VA received more rain than we did.

I would like to share a question I received from a grower today.

"With all of the rain events we have had lately and bloom being an important stage for fungicide application Should we spray after a significant rain event before the recommended 7-14 day interval? Specifically, I applied fungicide June 3rd and received quick but heavy rainfall on the 4th and 5th. Riding through the vines it looks as though there is still chemical residue on leaves and clusters. Can I base a decision off of this observation?"

It really depends on what you have sprayed, what we are expecting in the next few days, how the vines are maintained (shoot thinning, etc), cultivars, etc, so, I cannot give you a quick answer.

Typically, after drying, these fungicides stick pretty well with leaves and application rates are often time much higher that what you need to control diseases. Thus, even after considerable amount of rain and removal of spray residues, you can still achieve a good disease control. Please see this excellent article from MSU (http://msue.anr.msu.edu/news/fungicide_properties_and_weather_conditions) for more information.

However, since this is the critical time, I would be on a safer side. I don't think you have to spray today or tomorrow, but I may recommend to spray at 7-day interval, rather than extending it to a longer period. Depends on how the weather goes and target disease to be, but if you have a concern on downy mildew or black rot, this may be the time you want to use something with a kick-back activity (a phosphite or Ridomil product for DM, DMI for black rot). Powdery mildew fungus prefers dry weather, but if you have been struggling with PM in the past, and you are expecting a dry weather after this rain event, you may want to consider adding a PM specific material such as Quintec, Vivando, Torino, etc.

Also, as I noted in a previous post, some of you may have a rather long period of bloom due to damages caused by the April frost events. (For example, some of our Chardonnay vines are in full bloom today yet others are still lagging behind, which are probably on shoots from secondary buds) Depending on the situation, you may have to consider two applications for at bloom disease management especially to target Botrytis (e.g., Rovral, Elevate, Switch, Luna Experience, etc), ripe rot (QoI, mancozeb, zirum, captan, copper, etc), and bitter rot (same as ripe rot). It will get tricky, but please make sure to rotate FRAC codes!

Finally, I am not an entomologist, but this is also the time I start to see the incoming of grape berry moth in our vineyards. Please keep eye on them so that they won't cause damages on later in the season.

Friday, June 3, 2016

Another rain events in the forecast...

Our Chardonnay vines are getting close to full bloom, and of course, we are expecting more rain over the weekend. Just an another reminder that from bloom to 4-5 weeks after bloom is the critical period for downy mildew, black rot, and powdery mildew infection on clusters, and at bloom application is very important one for Botrytis management.  Please see recent post about the at bloom fungicide application consideration as well as recent updates on fungicides. This would be the timing where you will thrown in some good materials into your tank mix! It is much easier to protect the vines than try to play a catch up game after disease outbreak,