Virginia Grape Disease Updates

Grape Pathology Research Report 2011

2012-02-08T15:34:00.001-05:00

This is the document I should have included in the VVA handout. I thought about it, but forgot to include. If you are interested in the detailed reports of fungicide trials and also our recent activities, please check it out (pdf download).

Handouts from the 2012 VVA meeting

2012-02-06T12:44:00.003-05:00

First of all, a (belated) Happy New Year! I meant to upload some posts in January, but things were bit busy.

Second, thank you for those of you who attended the 2012 VVA meeting. It was very nice to talk to many of you at the meeting, and I am looking forward to meet you at either IPM workshops (Place and time, TBD, but we are planning to have it at multiple locations at the end of March, please check this blog and also email from Tremain), or in-season vineyard meetings.

Third, I have been asked from several of you to upload a color copy of presentations from the meeting, so here you go. This link downloads a pdf file from the beginner's workshop, and this link is for a pdf file of the talk about fungicide trials and discussions for 2012 season. (By the way, what I meant by "bee" in the presentation was "yellow jacket" as many of you have pointed out! ;) )

Next, many of you have asked me about pruning wound protection. As Tony described in the precious Grape Press, you can apply a product called Topsin-M to pruning wounds because VA has a special label. (i.e., it may not apply to your state, please check with your local extension agents!) Here's a link to my older post about the use of the product, which also contains a link to the special label. Please make sure to read the label. It has a 2-day REI. thus you cannot go back to the vineyard for 2 days. This product will give you a protection against Bot canker which can enter through pruning wound. Bot canker (caused by several Botryospaheria species) may or may not develop symptoms within a year or two, but there are evidence of long-term effect of this disease complex. If you are thinking about using it, please consider spray or paint only a part of your vineyard (= leave some part of vineyard untouched), so that you can obtain comparative data. If you wish, we can even set up a demonstration plot. Please contact me if you wish to talk about it.

Of course, the fungicide application is not the only measure against Bot canker, and I recommend you to think about alternatives. The double pruning that Tony described in Grape Press has been shown to very effectively protect your vines, and also I recommend not to prune if you see rains in the forecast. As with many other fungal diseases, Bot canker pathogens require water to be disseminated and to initiate infection. Also, if you will give a time for pruning wounds to heal, there should be lower chance of infection. Thus, it is better to prune when weather is warmer because the wounds tend to heal faster. In normal winter weather conditions, we probably do not have a high risk around this time of the year because the temperature is very low, but warm temperature we are experiencing and rains we have make me worry about Bot cankers.

Finally, as I mentioned at the meeting, our leafroll survey is about to be done; however, we are still accepting samples. We found very high number of virus-infected vines from our survey, thus, we would like to know more about them. If you would like to test your vines for leafroll viruses, please let us know. Thanks to the VA Wine Board, there will be no fees for testing.

If you have a difficulty sleeping at night...

2011-12-16T10:42:00.000-05:00

I recently published a book chapter with my colleague about how to optimize fungicide application. It is free to download, so, if you are looking for some bed time reading material, it may help you sleep. ;)

The title sounds like we are developing a practical application guide for fungicide, and that was our intention at the beginning, but we did not have a space in the chapter (and time) to explore that. Instead, we showed several examples of how research projects can be used to help optimize fungicide application. Hopefully we will have another opportunity soon to actually work on more practical chapter.

Handout from Beginner's workshop 2011

2011-12-07T15:58:00.000-05:00

Thank you for those of you who attended a beginner's workshop yesterday. It was a very good opportunity for me to talk to you. If you are interested in, we will hold another half-day beginner's workshop at next year's VVA annual meeting which will be held at Charlottesville in February.

Here's the copy of the handout from yesterday. Please click this sentence to download it. It is in Adobe PDF format.

I remember that I mentioned that I will post something about ripe rot; however, I have been busy. I will do my best to post the article in a few weeks!

Removal of clusters and canes from the vineyard?

2011-10-21T17:24:00.000-04:00

I just saw Tony sent an email this afternoon to discuss about the sanitation issues. I want to add a few more comments here to discuss this important issue. (by the way, if you would like to be listed to Tony's email list which he also uses to publish his quarterly publication "Viticulture Note", please let me or Tony know)

Since we finished the season with long rainy periods, some of you experienced increased level of downy mildew and/or Botrytis. In addition, I have seen several outbreaks of ripe rot (which I will discuss in the next posting), and other general rots (sour rot, Aspergillus, Penicillium, etc.). Because of that, we probably have a higher risk of having these diseases in the next season. The question is how to deal with them.

As Tony noted, it is probably a good idea to move them from the vines and place them in the middle of the row, then remove or mow. If the berries are hanged in the trellis, these can be sources of inoculum in the next season. Since many of these pathogens are splashed by rain, having a large number of spores right next to new growths is a bad idea. Also, by mowing the debris, it will help decomposition of these infected tissues. I have seen berry debris directly under the vines that were covered with Botrytis spores in the spring. Since there were no green tissues around, I do not know what it meant in terms of disease development for the season, but it just made me realized that they do survive through the winter in these tissues.

The question is what you can expect from these sanitation measures. Unfortunately, many of grape pathogens can complete their lifecycle in a short period of time (2-4 weeks), thus the effect of sanitation does not last long. Therefore, even if you do a good job of cleaning up your vineyards, it will not allow you to skip any of early season sprays. However, it will help reducing the risk of outbreak early in the season. If the environmental conditions were very favorable and there were abundant spores, you may face the risk of outbreak from the get-go of the season.

Tony covered about cluster, but how about canes and pruning woods? The same principal will apply here. However, the difference is that these woody tissue are more resilient to decomposition, and some of pathogens, such as Phomopsis, Botryosphaeria, and Eutypa can survive in the woods for several seasons. Since both Phomopsis can Botryosphaeria can produce spores from the infected 1st year cane, if you leave them on the ground, chances are they can be the source of inoculum for the next season. Spores of both pathogens are splashed by rain (some of Bot species can produce airborne spores, but it seems that rain splashed spores are the majority), thus, the closer the canes to the main trunk, the higher the risk is. Say, if you have infected canes nearby trunk and the trunk is damaged from winter injury or other means of wounding event, you can easily imagine that these pathogens move into the wound and cause problems later. Thus, it would be nice to remove pruned canes from the vineyard, or at least chop them down in the middle of the row.

If you are making a big cuts, make sure to take them out from the vineyard. You are cutting big pieces probably because of diseases, and leaving these old trunks or cordons in your vineyards won't do any good for you.

Fenarimol will be taken out from the market

2011-10-07T13:37:00.000-04:00

I just learned that Fenarimol (Rubigan® AS, Vintage® SC and Focus®, from Gowan) will be taken out from the market soon. It was due to their business decision. The company will sell and support the fenarimol brands Vintage SC and Rubigan AS through December 2012. Gowan is in discussion with EPA to voluntarily cancel its fenarimol registrations.

The distribution channel typically has 2 years from the official date of cancellation to sell existing inventory of fenarimol products. Growers typically have no time limitation to use up fenarimol products they have purchased. (Please remember to keep and follow the label!)

It is sad to loose a good product that can be an alternative option for our powdery mildew. It belongs to group 3 in FREC code (Sterol Inhibitors or SI), thus, the mode of action is the same as other SI's, such as tebuconazole, myclobutanil, etc.

Rains and rots

2011-09-29T17:03:00.000-04:00

Boy, it has been a rainy month of September!
If you are subscribing to Mark Chien's "Wine Grape Information from Penn State", you probably seen this, but here's a link to NOAA on the precipitation record from Irene and Lee. It gives you an idea of how we started this month with a lot of moisture in the air. As you can imagine, this type of weather will increase risks of having late season rots.

I have heard some people had an outbreak of Botrytis, sour rot, ripe rot, etc. The pictures above are examples of Botrytis bunch rot. The management strategies for these rots are discussed in the previous post. Since temperature during these rain events were low and we have not have many days with sunlight, you may want to keep your clusters hanging little longer. Please keep remind yourself about the PHI when you decide to apply fungicides.

One of the strategies for sour rot and Botrytis management discussed was the management of birds. Tony's group has been using a bird netting, and here's the good picture of the efficacy of it. As you can see, the clusters inside of the net are not damaged while the ones outside of it are gone.

Also, if you take a look at the first picture of Botrytis, you will notice that the berries at the top side of the picture was damaged by either bird or bees. It is not uncommon to see the start of Botrytis on the damaged berries since it can grow on higher sugar contents than many other pathogens.

The other concern is on the foliar infection of downy mildew, which can also cause defoliation. It is important to keep these leaves healthy to have a good accumulation of carbohydrates to the trunk. At this point, we need to concern about the PHI, thus, the materials you can use against downy mildew is limited. Both captan and Phosphorous acid materials have a 0-day PHI (Note: captan has 48-72 hour REI).

Because we had many extended wet hours, some of you are having potential issues with molds growing on the surface of berries. The one I saw at several places are the ones look like sooty mold on apples. We know that the sooty mold of apple is caused by numerous species of fugal complex, thus, I would expect the same. These fungus are surviving on some nutrient matters on the surface of berries and probably the infection is superficial. Apple growers are applying captan for it, thus, I assume we can do the same.

I have heard that in the mast, these molds (or spores of them) sediment on the bottom of the tank, and probably do not cause any ill effects. However, unfortunately, I do not have much information. If you have experience to share, please let me know.

Rain, rain, rain, again... Botrytis, Sour Rot, and Downy??

2011-09-08T23:05:00.001-04:00

I thought I would wait until the rain stops to update the blog, but rains are keep coming and even when we do not receive precipitations, the air has been so damp that the relative humidity has been above 90% for a while. It started late night on 9/4, and still going. So far, I counted about 90+ hours of estimated leaf wetness. The temperature has been between low 60's to mid 70's. This has been ideal condition for both Botrytis and downy mildew to develop. As for downy mildew, your berries should be resistant to infection, thus, concern is on foliage infection. Vines need healthy leaf areas for accumulation of carbohydrate into main trunk in order to survive the winter. With a concern on the PHI, one of Phosphorous acid or Phosphonate materials should be a good choice. They also provide a good kick-back activity too.

I have covered Botrytis earlier in this blog, so, please click here and here for more information. If you decided to make an application, please be aware about the PHI, some Botrytis materials have a 14-day or longer PHI.

You may also concerned about sour rot. In general, sour rot control need to be based on general vine management because it is typically initiated with a wounding event (insect, bird, hail, etc). Thus, the first question is whether they have issue with bees or birds in their vineyards. If they do, management of bees and birds will be the first priority.

The other potential causes are early infection by either powdery mildew or Botrytis. When powdery mildew infect berries early in the season, skin can erupt as berries getting larger. When Botrytis infects flower, it can resides in fruit tissues and cause disease when berries are mature.

As for protective chemical, a product called Switch lists sour rot and Botrytis. Switch has a 7-day PHI. Other options are Pristine, captan, and ziram. It seems that all of them provide some level of protection against sour rot, and rotation on captan and ziram showed a good efficacy on one of trials done in PSU. Since we may be potentially dealing with a fungal complex (general yeast, Penicillium, Alternalia, etc), I tend to recommend use of captan or ziram because they are less prone to have fungicide resistance. Ziram has a 21-day PHI, so, it is probably not the best item to be used at this time of the season. Captan has a 0-day PHI (with a 48-hour REI).

Disease risks from weekend's rain

2011-08-29T17:09:00.000-04:00

Irene stayed little longer than I expected in our area. At the end of Sunday, Winchester area received a total of about 0.5 inches of rain. I was monitoring the RH for last 2-3 days, but it was below 90% (actually it was 60-70% in most of time between rains). It was probably because of high wind due to Irene. Based on this information, the risk of Botrytis is not high; however, as with any precipitation events, it varies dramatically even between short distances. (For example, our AREC station received 1.2 inches or so from Irene.) Thus, please check your local weather service.