Monday, October 8, 2018

Disease management after harvest

Many of you are about to be done with harvest and some may still have a few more weeks to finish this rainy season. This is a reminder for disease management after harvest.

The main reason for you to keep your vines clean after harvest is for winter preparation. Grapevines need to store carbohydrate to survive the cold temperature during the winter. If there is not enough foliage on the vine, it may increase the risk of winter injury. The main target diseases are downy mildew and maybe powdery mildew. I do not typically worry about powdery mildew at this late in the season, unless you already have an on-going outbreak that started a few months ago. Downy mildew is common after late-August in our area and severe infection can result in defoliation. Therefore, in a typical year, downy mildew is the one that I would like to control after harvest.

Since it will be after harvest spray, you do not need to worry about the PHI (pre-harvest interval). Thus, you can apply a combination of mancozeb + sulfur, or simply a fixed copper by itself, especially if you are not too concerned about powdery mildew. Depends on the cultivar, you may need to spray once or twice in a two-week interval.

Monday, September 10, 2018

Spray before the upcoming storm?

I received several emails and phone calls concerning spray before the upcoming hurricane Florence.

Hopefully, we will have a window of opportunity to apply materials. Looks like we have a break from rain starting tomorrow for maybe 1.5 to 2 days.

Here is the list of materials with low PHI (same as the one I posted last month).

Just FYI: here are previous posts about...

Once you have about 1.5-2 hours for the materials to dry after application, that will be sufficient for them to stick to the leaf and cluster surface. Good luck!!

Tuesday, September 4, 2018

Reminder: Extension meeting tomorrow!

Field day: Use of Protective Covers to Reduce Fungicide Usages in (Organic) Wine Grape Production in Virginia

5 September 2018

1 – 4 pm


595 Laurel Grove Rd.

Winchester VA 22602

Mizuho Nita, Ph.D, Virginia Tech

The total acreage of certified organic grape production in the US has increased from 12,575 acres in 1995 to 38,664 acres in 2011. However, only three Virginia vineyards have been approved by the USDA for their organic management practices for wine grape production, and only two have a winery as of 2018. The main reason why organic wine grape production is not common in VA or any other states located the east of Rockies is fungal diseases, which are driven by frequent rain events during summer months. Thus, the Nita lab has established two experimental vineyards with financial aid from the USDA/NIFA VDACS Specialty Crop Research Initiative Block Grant in 2012. Although we identified several cultivars that may do well with the organic practice, there are two significant challenges: a disease called black rot, which none of the OMRI-certified chemicals works sufficiently, and a potential loss of copper fungicides due to a trend of tighter regulations in other countries.

Rather than searching for other chemical components, which is usually in the hands of chemical companies, we proposed to the USDA’s Southern Region Sustainable Agriculture Research and Extension (SARE) on-farm grant to examine the efficacy of various paper bags or umbrella to individually protect grape clusters (grant ID: OS17-107). These bags and umbrellas are made out of water-resistant paper, designed to fit grape cluster, easily applicable with an embedded wire, with small holes for ventilation and water drain, and expected to last for a whole season.

Based on 2017 data, the bagging practice significantly reduced disease incidence and severity of black rot. Also, it showed that the earlier the timing of bagging, the better the result. Although application will be very labor intensive, a conversation with our farmer cooperator, Mr. Hambsch at Loving Cup Vineyards, revealed an extremely high cost of intensive removal of disease berries is necessary for his production. Thus, this method can be a good alternative method to reduce the intensity of the diseases. Although we tested out the bagging for the organic practice, it can be used for the conventional grape growing, especially if you are concerned about disease and fungicide residues on berries.

In this field day, I would like to invite you to visit our experimental plots in the AHS AREC to see these bags in action and discuss our findings.

Tuesday, August 28, 2018

Late season fungicide options (= materials with short PHI)

At Winchester, the night time relative humidity has been still very high, close to 100%, in nearly every nights in the past three weeks. In addition, we have been observing rapid development of thunderstorms, pretty much every day in the past few days. I know I sound like a broken record, but these conditions favor downy mildew development because downy mildew pathogen prefers to produce spores under dark, humid conditions. Then spores will be spread via rain.

At this point, you do not need to worry about downy mildew infection on clusters; however, they can still infect leaves. Often time, you will initially see infection on the top of the canopy because younger leaves are more susceptible than older ones. Losing the top leaves and laterals are not a big deal; however, once the infection gets severe, it can defoliate many leaves rather quickly (as in the picture above), and that can affect maturing process. Knowing how wet this year has been, it is probably wise to be proactive on downy mildew management.

As usual, it is much better and easier to have a preventative program than trying to play the catch-up game. There are many good protective materials for downy mildew, such as Revus products, Zampro, Forum (Please note that these three share the same mode of action (FRAC=45 (+ 40 for Zampro), and Ranman (FRAC=21). In our small trial, fixed copper (FRAC=M1) worked pretty well against downy mildew when we compared with captan (FRAC=M4). Captan worked too, but a fixed copper product lasted longer than captan. However, some wine makers do not like to see captan or copper used late in the season, so, this time of the season maybe the best timing to use copper and captan for downy mildew. You can also use a phosphorous acid product (FRAC=33) as well (watch out for the rate!). For some cultivars, you may still use zirum (FRAC=M3) which has a 21-day PHI. Please mix and match to rotate among mode of action groups.

Downy is not the only disease you need to consider. The risk of Botrytis outbreak can be high with all the moisture in the air. Typically, I post end-of-the-season application tips in September, but it looks like the season is going much faster than a typical year for many of us. Thus, here is a list of fungicides with relatively short PHI (7 days or less) (a PDF file to download). I cannot cover every single fungicide out there, but I tried to cover common ones. Wine making considerations can influence fungicide uses close to the harvest too. Make sure to communicate with your wine maker(s) if they have a preference on the use of fungicides, especially copper and captan (I listed several copper materials because they have different PHI or REI.)

As I noted in one of previous posts, make sure to rotate mode of action for Botrytis because Botrytis pathogen is known for quickly developing fungicide resistance. I prefer to see a mode of action to be used twice or less per season, especially when we deal with Botrytis (with an exception of fungicides with FRAC code starting with "M"). Once again, wound management is very important to reduce the risk of Botrytis. Managing the source of wounds such as insects (esp. grape berry moth), or birds, or powdery mildew at early in the season, can positively impact Botrytis management. Also I should note that sour rot pathogens also going after wounds.

Tuesday, August 7, 2018

Just another reminder on downy mildew

In the last several days, the nighttime relative humidity has been very high (>90%) and temperature has been in the upper 60s ~ lower 70s. This condition is favoring spore production of downy mildew.
Please check my previous post about downy mildew management.

Wednesday, July 25, 2018

Reminder on downy mildew

Just a reminder on downy mildew management: although the month of July was dry until this week, many of us had a very wet early summer that fostered downy mildew development. In addition, during the last several days, the night time temperature was in low 70s and RH was 95-99%, which was an ideal condition for downy mildew spore production.

Thus, if you have not, make sure to protect your vines against downy mildew when you have a chance. If you think you have missed the window, we still have some options.

We have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=P7, Prophyt, Phostrol, etc.). One of two Ridomil product (Gold MZ) has a mancozeb, which has a 66-day PHI, so, unless you have a late season red, you probably need to use the other formulation, which is Ridomil + copper. Both Ridomil and phosphite are good with kick-back, but you probably want to add a protective material to cover both directions. Examples would be captan (FRAC = M4), or ziram (FRAC = M3), or Revus, Forum (FRAC=40), or Zampro (FRAC=40+45), or Ranman (FRAC = 21)). Please note that Revus, Forum, and Zampro all have the same mode of action (i.e., you cannot rotate among these three.) Also, copper materials (FRAC=M1) works well against downy mildew. If you decide to use a copper, my current preference is one of newer materials (e.g., Cueva, Badge, etc.), which have a lower copper concentration (but still works well).

As Tony indicated in his newsletter, keep eye on the concentration of the phosphite material. If you exceed the amount, it may end up with phytotoxicity.

Many people have asked me about the combination of copper and phosphite. I have heard that there is a pre-mixed product of copper and phosphite sold in Europe, so, these compounds can be mixed. However, both products are sensitive to water pH. It needs more research, but I have a feeling if you miss the sweet spot on the pH, it can cause toxicity on vines. So, if you wish to try, my recommendation is to make sure you have a good pH (close to the neutral), and try it on a small block of your vineyard (or even a few vines). Also, I wonder about different copper formulations (sounds like a good summer project for us. we will see...)

Wednesday, July 18, 2018

Handouts from today's sprayer workshop

Thanks again for coming to today's vineyard meeting. I learned quite a bit!

Here are my handouts (sorry for not bringing enough today!!)

1) Sprayer calibration handout (will open a PDF file)
2) Sprayer calibration aid (spreadsheet)
(In order to use it, please download onto your computer [File -> Download as...])
3) Seasonal grape disease reminder (will open a PDF file)