Friday, April 29, 2016

More on Phomopsis and other disease concerns

Well, it looks like we will see more rains coming in next week or so. Sounds like a typical start of the season for VA vineyards, doesn't it?

Since most of vines have 2-10 inches of shoots, our main focus will still be Phomopsis, especially if your vineyard(s) experienced Phomopsis in the past.  At Winchester, we are experiencing 27+ hours of wetness with the average temperature of 48F or so. This will be a low Phomopsis risk event, and counting.

Plus, especially if you had a serious downy mildew issue in the past season, it may not be a bad idea to think about downy mildew because the next series of rains for this weekend and early next week may happen when air temperatures will be in 60's and 70's.  As for Phomopsis, a protective spray of mancozeb, captan, etc. is pretty much the only mean of management, but we do have some options for downy after the rain event.

So, if you did not spray before this series of rains, but you are lucky enough to have a window for a spray before the big rain on Sunday, you may want to go ahead with it. I would go with mancozeb (if your aim is Phomopsis alone) or add a phosphite (Prophyt, Phostrol, etc.) to the mix, if you have a reason to believe downy could be an issue at your location. Also, trial reports from Michigan State showed that a phosphite would work against Phomopsis too. (I am not sure that it can have a kick-back activity, though)

If you won't have a chance before Sunday, or you have applied before this week's rains, then I would add a phosphite to the next mix of your fungicide application. As I mentioned above, I am not sure it can have a kick-back activity against Phomopsis, but at least it will provide a good kick-back activity against downy mildew. It looks like the next opening will be on or after Tuesday.

FYI: For our plots, we sprayed mancozeb earlier this week before the rain for older Chardonnay plot where we started to see Phomopsis in the last two years, but did not spray "organic" plot where we have not seen Phomopsis. The timing for next application will be either late next week or early in the week after, depending on the weather conditions.

Friday, April 22, 2016

Disease management after frost events...

Several growers contacted me recently to discuss about disease management after recent frost events. Here are my take on it.

1) If you have some damages on your shoots/buds.
As usual, you work with the growth of the vine, but not with the calendar dates. If you have lost a lots of growth from the primary buds, you may have to start over your spray program.  If you have mixed growth from the primary and secondary buds, you may need to adjust your spray program based on what may come from the secondary buds, especially around bloom. Flowers from the secondary buds may lag behind, thus, you may need protect flowers for a longer period of time.

2) If you have extensive damages on your shoots/buds to the point that you may not able to expect crops.
Based on what I heard, we are not seen this scenario this year. However, if you happened to have the major issue from the frost events, well, first of all, I am sorry.  Second, you still need to have some level of disease management in order to keep canopy clean so that your vines will crop next year. Vines probably need a decent canopy management to have good penetration of lights to encourage flower cluster formation for next season as well.

If you are not expecting crop this year, you can treat these vines as you may do for younger non-baring vines. You can use a mix of mancozeb and sulfur, or a fixed copper by itself (especially if your vineyards do not have a bad history of powdery mildew) and spray every 10-14 days.

Once again, the main target at this time of the year will be Phomopsis cane and leaf spot. Looks like we are expecting several days with some chance of rain over next 10 days or so.

Here's an update from our vineyard. As I noted earlier, our younger Chardonnay vineyard was hit very hard.  It was not as bad in some vines, but I am still expecting close to 70-80% damages on some vines. For some, like the one from the picture below, we may need to be retrain from lower shoots since majority of buds look very bad. We will see how the secondary buds will do.

Buds on older Chardonnay vines were tighter than the ones on younger ones when we experienced several days with mid-20's. Damages based on visual assessment were about 5-20%, depending on the vine. Some vines may have a looser canopy later, but nothing seems too serious.

[Please note that long internodes above the buds are for our experiment (we are looking for trunk diseases), you should not have these on your vines. ;)]

Our other cultivars, Cab sauv and Cab franc were most likely tight enough at the time of frost events.  I did not see any damage on them.

Friday, April 8, 2016

Spring cold injury and insect damages...

As with many other places in the VA, we were suffering from frost damages.  We experienced several near freezing events this year, and most notably, a few hours of 25F on Thursday morning. Our younger Chardonnay planting (4th leaf) had a bud break around 4/1, and being suffered more from it.  I estimated about 80-90% of emerged shoots are now gone. Our older Chardonnay (8th leaf) is about a week behind, and my visual estimate as of yesterday was about 25% loss.  Some buds/shoots look like they are surviving, but I am not sure how it will go after tomorrow morning...

There is a very nice blog post about spring frost from Dr. Michela Centinari at PSU.  If you are interested in, please follow this link.

The other items I noticed in our vineyards is damage from climbing cut worm.
For us, it always starts from the Eastern side of our vineyard which is facing a small patch of wood.  If it is a warm weather, I would spray for it, but I think I will wait until the temperature gets warmer near the end of next week. Here's an information page on climbing cutworms from Doug.

Monday, April 4, 2016

Early spring disease consideration: Phomopsis cane and leaf spot

Our 7-yr old Chardonnay vines are in bud swell stage, and others are tagging along.  It looks like we will see bud break in a week or two.

One of diseases you need to consider this time of the year is Phomopsis cane and leaf spot.  It causes minor leaf spots, but more importantly, it can cause necrotic lesion on shoots and rachis.  It also causes berry infection; however, it is not common with wine grapes because of our spray programs.  Materials for black rot and downy mildew are often effective against Phomopsis, thus, the coverage for these diseases are also working as management of Phomopsis, especially later in the spring/summer.

Phomopsis takes a while to establish in the vineyard; however, once it is established, it is difficult to get rid of this disease.  Some varieties, such as Viognier and Seyval blanc, are more susceptible to Phomopsis than others.  Phomopsis tends to become noticeable as a vineyard gets older because of it life cycle. The fungus survives in canes and trunks that were infected in previous years. (= Please remove old trunks and cordons when you retrain the vine!)  During the spring, it will produce spores that are splashed by rain onto new tissues.  It produces spores only during the springtime. Thus, luckily, unlike other diseases we face, there are only one major infection period throughout the season.  Phomopsis spores can cause infection under relatively cooler environment (upper 40s).  Thus, springtime rain events are ideal for Phomopsis to produce spores and cause infection. Therefore, it is important to protect young tissues when they come out from the older canes and trunks.  

If rain events are coming into the picture after bud break, mancozeb (Penncozeb, Dithane, etc.), Ziram, and captan are an effective protective material against Phomopsis.  (QoI, such as Pristine, works too, but you don't want to use them this early in the season.)  Protection is the only mean of chemical management because no materials are effective after the infection.