Guidelines for Developing an Effective Fungicide …

1 Fungicide Spray Workbook for Virginia Wine Grape (2012) Page 1 April 2012 Workbook for Developing an Effective Fungicide Spray Program for Wine Grapes in Virginia, 2012 Mizuho Nita, Ph. D. Research/Extension Grape Pathologist Virginia Tech, Alson H. Smith, Jr. Agricultural Research and Extension Center 595 Laurel Grove Rd. Winchester, VA 22601 Phone: 540-869-2560 ext. 33 Email: I have a blog where I discuss grape disease management issues almost daily during the season. Please visit here: Also, my webpage at Virginia Tech has been changed to: The purpose of this workbook is to help wine grape growers in Virginia develop an Effective Fungicide spray program for their production. The targeted diseases are: powdery mildew (PM), downy mildew (DM), black rot (BR), Botrytis bunch rot, and Phomopsis cane and leaf spot (Ph). Any of these diseases can be a significant threat to yield if an outbreak occurs.

2 The proposed spray schedules intend to provide a simultaneous control of these five major grape diseases, and include several options that you could use as Guidelines for your program. The workbook does not include all fungicides registered in Virginia for control of these grape diseases; thus, two supplemental tables are attached for your reference. Table 3 shows the effectiveness of Fungicide you may select, and Table 4 lists fungicides that are prone to the development of Fungicide -resistant pathogen isolates. This information is merely suggested Guidelines , and it is designed to serve as food for thought . There are many things to be considered beyond these Guidelines , such as specific characteristics of your vineyards, varieties, training systems, diseases present in the field and their history, local weather patterns, your budget, etc. It is important to make sure that your program addresses these issues, and provides a good management of diseases while it fits your budget.

3 Fungicide prices vary by year and location; thus, make sure to calculate cost per acre as you plan your program. The schedule I m presenting here is based on commonly used fungicides such as mancozeb and sulfur products. It is simply because these products have lower risk of Fungicide resistance development and generally cost less. However, I am not endorsing any particular products. This information is not a replacement of the existing spray guide (Pest Management Guide, or PMG) from Virginia Tech. Please think of this as a supplemental workbook that focuses on disease management. Intention of this workbook is to add a little more detail on the Fungicide spray program to help you develop your own program. PMG for grape can be found at ( ) Finally, please read and follow the Fungicide label. As you know, the label changes all the time. Although the effort has been made, because this guideline presents quite a bit of information, some may not be current.

4 [If you find a typo or confusing point, please feel free to contact me.] The label should provide information on allowable usage rate, cautions and restrictions on use, and recommendations on Fungicide resistance management strategies. [New for 2012. I am converting this guide into a workbook that fills the gap between the PMG and your Fungicide template/record. It is still a work in progress; so, please send me any comments or suggestions!] Fungicide Spray Workbook for Virginia Wine Grape (2012) Page 2 April 2012 Review of 2011 season As with last year s version, I would like to start off with this guideline with a review of 2011 season. I will cover mainly about what happened in Winchester area and in our experimental vineyards. As you know, each location is unique, but I am hoping that this review will help you remember what happened in your vineyards so that it will help you plan this season s planning.

5 Bud break to bloom: Bud break of 2011 was about the average for us in Winchester. It was 14 April for Chardonnay and Cabernet sauvignon followed it 5 days after. From bud break to bloom at 28 May, we had 15 rain events that were considered infection period for one of common early season diseases: Phomopsis (pictured below), or downy mildew, or black rot. Since temperature during the rain events were relatively warm (in mid-60 s), some of you might have experienced more than usual Phomopsis or black rot. As for downy mildew, we did not observe notable development of downy mildew despite of rain events before bloom. One of the reasons is that we observed only a few numbers of nights where temperature is above 55F and relative humidity was very high (>85%). Such condition promotes spore production of downy mildew. Also, I think overall level of inoculum was probably low in our area because 2010 was relatively dry, especially toward the end of the season.

6 Bloom to veraison: up to the first week of July, we were receiving rain constantly. I counted six infection events for Phomopsis and Black rot, and eight for downy mildew. At the same time, periods in between rains were dry. This condition (plus abundant inoculum from 2010 season) promoted development of powdery mildew in our vineyards. As with 2010 season, it started early (around bloom), and by the time the berries are BB size, I recorded more than 50% disease incidence in our control (minimum sprayed) vines. Also around late June to early July, folks in central VA experienced a series of thunderstorms that came with hails. In addition, probably due to rain and cloud cover during that period, some of us observed development of Botrytis on clusters. Since this pathogen likes high sugar contents, it tends to appear when berries are maturing, but under humid conditions, it can infect younger berries.

7 Then we experienced a dry mid-summer. There were rains here and there, but none of them were significant. In fact, it was so dry that birds started pecking on grapes in early part of August. I went to a conference for 10 days, and when I came back, all my berries are gone! Good thing was that I was not using them for my experiments this year. At that point, I thought maybe we would have another year like 2010. Well, I was wrong! We experienced three days of rain from Irene in the end of August, and then Lee hit us. During the month of September, Winchester area Fungicide Spray Workbook for Virginia Wine Grape (2012) Page 3 April 2012 received inches of rain, and I counted only a few days without rain or cloud cover. Veraison to harvest: Unfortunately, rain did not stop there. We received continuous rain throughout the month of October, dropping inches of rain in Winchester area.

8 When berries are exposed to such a long and consistent wet conditions, pathogens won t give them a break. What many of us experienced were downy mildew (on foliage or severe enough to cause defoliation), Botrytis bunch rot, sour rot, ripe rot, and sooty-mold like dark mold. Sour rot requires wounding event to cause disease, and Botrytis can take an advantage of wounds as well. That means that controlling birds and yellow jackets or hornets reduce the risk of Botrytis and sour rot development. Local bird population differs, but in general, bird netting and calling machine are two good tools for managing birds. As for yellow jackets, use of commercial trap during the early part of the season to prevent a queen to build a nest nearby vineyard can reduce the risk of emergence at latter part of the season. I have been hearing more about ripe rot since 2010 season.

9 The pathogens (Colletotrichum acutatum and C. gloeosporioides) tend to prefer warm weather (as we had in 2010), but last year s prolonged wetness made ripe rot appear again regardless of cooler weather. Although it does not cause significant rots in many cases, even a small amount of spores of ripe rot pathogens (3%) are known to affect wine quality. Based on a small experiment we conducted in 2011, we have confirmed that these pathogens can infect berries regardless of their developmental stage. ( , mature grape berries do NOT develop resistance against this pathogens.) The severe infection also cause berries to shrivel or shrunk while the rachis of infected clusters tends to be clean ( , clusters on the left-side of the picture below). I found peduncles showing some discoloration, so, it seems that the pathogens infect berries then move toward green tissues.

10 Although captan is listed as one of Effective compounds, a recent study showed that one of pathogens of ripe rot is insensitive to captan. Literatures show mancozeb and strobilurins are Effective against ripe rot. Thus, if you cannot control ripe rot with captan, Pristine or other QoI (Aboud, Qadris Top, Sovran, etc) can be a good option. So, what we should expect for this season? Due to last year s conditions (= environment conducive for powdery mildew during early then became very wet for downy mildew development), some of you probably face higher risks of these diseases than a typical year. If you are concerned, make sure to have some materials that work against these diseases. A simple combination of mancozeb and sulfur suffice to provide early season protection (plus mancozeb works against Phomopsis and black rot), then, switch to newer materials, such as DMIs, around pre-bloom spray.