Thursday, July 30, 2009

Rains in the forecast

It seems that we have more rains on the horizon. I hope you had a chance to protect your vines, it it was not done recently. At Winchester area, yesterday's rain events were sporadic and it was not significant disease event except for downy mildew, but some of nearby area probably had more continuous rains, thus you need to check your local weather. We have having 13 consecutive nights that favors downy mildew sporulation, thus even though the threat on fruits are gone, you may want to consider downy mildew materials to protect your foliages.

Monday, July 27, 2009

Many thunderstorms...

We had a series of thunderstorms passed by the area. In terms of the duration of rain, all are short; however, it was wet afterwards because many of these rains happened after 5pm and the relative humidity stayed high until following morning.

On 25th, we had rain started from 9:40 pm and RH was high until 10:00 am next morning (>12 h of wetness). On 26th, the strong thunderstorms passed starting 5:00 pm, and RH was high until 8:00 am this morning (>15 h of wetness). Average temperature during these events were mid-60F, thus, infection of downy mildew, black rot, Phomopsis, and Botrytis could happen. But as I mentioned several times here, if you passed the critical period (4-5 weeks after bloom), your berries should be resistant to downy mildew and black rot infections.

Since we had such a strong wind with the thunderstorms, some of you may have experienced damages on berries (and/or even shoots and trunks). Hopefully they will dried out, but these wounds can be a course of entry for Botrytis and other rotting organisms. This (from bunch close to veraison) is the time for protection against Botrytis nonetheless, so, I would recommend including a Botrytis fungicide in your next application.

Friday, July 24, 2009

Rain after rain....

We had a series of thunder storms on Wednesday and last night. The condition of air were dry to begin with, so, the relative humidity did not stay high after the rains (stayed in 70% range). Thus, these rains probably did not account for disease event at Winchester; however, your vineyard might had more rain or longer rain. Please check your local weather.

Also, we are still having 7 consecutive nights with conditions for downy mildew sporulation. Even with a short rain (>90 min), it can cause an infection, thus, if your berries are still in a critical time (4-5 weeks after bloom), and you see leaves with downy mildew in your vineyards, then you may need to react to these series of infection event with Phosphorus acid or Ridomil products. However, if your berries passed the critical time, the risk of infection is very low.

Once again, the fungus you may need to concern at this point is Botrytis. Make sure to protect your bunches with Botrytis materials (please read previous posts (2-3 post ago) for details).

Wednesday, July 22, 2009

More rains in the forecast

Rain on this Monday did not last long, but since it started later in the day, the relative humidity was high (>90%) until next morning. Thus, we had >15 hours of wetness event with an average temperature of 68F or so. This accounts for infection event for Phomopsis, downy mildew, black rot, and Botrytis, and ascospore discharge for powdery mildew. And I'm aware that areas in the south of us received more rain last night. Please check your local weather record.

In addition, we are having five consecutive nights with high relative humidity that favors downy mildew sporulation. If you have issues with downy mildew this year, you may need to take some action before or after next round of rain. (but again, it depends on growth stage of your berries. If it is past 4-5 weeks after bloom, the risk of downy mildew infection on berries is very low.)

Unfortunately, there is no curative fungicide for Botrytis, thus you need to protect your berries against infection. As I mentioned in the previous post, often time, protection at berry touch and at veraison is recommended. Please refer to either my spray guide or VT's PMG for list of fungicide you can use.

Saturday, July 18, 2009

Two wetness events recorded on Friday

We had two wetness event due to lines of rain passed by yesterday (7/17/09). The first one started around 11:30 am, and wetness lasted until 3:30 pm or so (4 hours) with an average temperature of 71F. The second one started around 8:40 pm and wetness lasted until 2:00 am (6 hours) with an average temperature of 66F. These events accounted for downy mildew infection, potential powdery mildew ascospore discharge, and light infection for Botrytis. Both are little shy for black rot infection event.

As I mentioned in the previous post, your vines should be very close to the end of the critical period. After it is done, you can relax a bit in terms of downy, powdery, and black rot infection on berries.

More rain events are in the forecast on Monday to Wednesday.

Wednesday, July 15, 2009

Rains in the forecast, and a vineyard meeting at Pollak Vineyards

There is a vineyard meeting tomorrow at Pollak Vineyards from 11 am. I won't be there, but here is my handout for tomorrow, which talks about risks of diseases at this point and a disease update at Winchester. Tony will be there to discuss about viticulture topics.

There are chances of rain in next few days in the forecast. However, so far, we haven't had a night which favors downy mildew sporulation for a while. In addition, your berries should be developing resistance to downy mildew and powdery mildew at this point (4-5 weeks after bloom).

For black rot, it may take little longer (up to 8 weeks after bloom, depends on variety), thus, please scout your vineyards for black rot. Black rot fungus takes about 2 weeks from infection to sporulation. Thus, you do not see it right now, your risk is low because there is not enough time to have an outbreak. If you have some degree of infections on berries and leaves at this point, and if you are concerned, Rally (myclobutanyl) is a good product that you can apply after the rain.

Monday, July 13, 2009

Another dry weekend :)

We haven't experienced major disease event for a while. On 7/9-7/10/09, we had two consecutive nights that were favorable for downy mildew sporulation, and on 7/11/09, there was a short thunderstorm (~ 1 hr, 75F, 0.42 inches). It dried up quickly, thus, it may or may not be long enough for downy mildew infection (~ 90 min is required). For some location, it might been an infection event, so, please check your local weather record.

Most of your vines are getting close to the end of the critical period (bloom to 4-5 weeks after bloom) for berry infection by powdery mildew, downy mildew, and black rot. After this period, you can relax a bit.

The next disease to be considered is probably Botrytis. There is no formal study done yet, but many growers experienced that if you apply fungicide before bunch close and varison, the risk of Botrytis outbreak decreases. I think the logic behind it is that the application before bunch close provide a good spray coverage for both outside and inside of the bunch, and the application before varison adds protection when more Botrytis spores tend to be present in the air. There is no fungicide with a curative activity against Botrytis, thus, preventative application is important.

Wednesday, July 8, 2009

No, it's not chocolate truffle...

On Sunday and Monday morning (7/6 and 7/7/09), we had relatively high relative humidity (>80%) at night which favor downy mildew sporulation. Thus, if downy is your concern, you may want to scout your vineyard. (But remember that it requires rain for new infection.)

As I mentioned several times, we have an experimental plot where some of vines are not treated with any fungicides. On these vines, black rot, powdery mildew, and downy mildew become very severe. Last time I showed black rot, so, now it's a turn of powdery mildew.

Powdery mildew on upper leaf surface

Powdery mildew on bunches... No, it's not truffle...

Powdery mildew on a cane

Monday, July 6, 2009

It was a nice and dry weekend

I hope all of you had a nice 4th of July weekend. I'm glad that we did not see the forecasted thunderstorm events.

Most of vines should be approaching the end of the critical period for powdery mildew, downy mildew, and black rot infection on berries. Berries of V. vinifera varieties become resistant to infection after 4-5 weeks after bloom. (V. labrusca vines become resistant after 2-3 weeks, hybrid varies.) These pathogens still can infect, but the success rate declines rapidly after this period. In Winchester, >50% bloom was observed on Chardonnay on 6/6/09 and on Cabernet sauvignon on 6/9/09; thus we have about a week to 10 days to go.

After this critical period, weather condition in VA typically becomes unfavorable for downy mildew and black rot (hot and dry), and powdery mildew control becomes a key issue. Please scout your vineyards for diseases and adjust your spray schedule accordingly. Also, this is about the time Japanese beetle becomes an issue. I've heard that wet spring tends to support their population, so, keep your eyes on them too.

Friday, July 3, 2009

Happy 4th!

The thunderstorm on 7/01/09 lasted a little over an hour (0.73 inches); however, RH remained high for about 9 hours with an average temperature of 65F. Thus the event was long and warm enough for Phomopsis, downy mildew, and black rot infection, and powdery mildew ascospore discharge.

Also, we had nights with relatively high RH (>80%) in 6/29 and 7/2. If these are isolated events, you do not need to worry about; however, as we know, the early part of June was very wet and we had many nights with a favorable condition for downy mildew sporulation. Sure enough, when I checked vines yesterday, we had a lot of sporulations under side of leaves.
If you have seen these spores on many of your leaves, you may want to think about protecting healthy leaves and berries from next infection event, or use materials with a curative activity (Phosphorus acid, Ridomil etc).

The other disease I found quite a bit in our untreated vines are black rot. This is one of diseases which you really need to be on top of it to secure your yield. Here are some convincing pictures.

Here, you can see a path of infection from a leaf to berries...
Now you can clearly understand why it was named black rot...
Once again, the critical period of infection on berries for black rot, downy mildew, and powdery mildew is 4-5 weeks from bloom. If you protect your vines during this period, you should not see damages like these. In fact, a vine next to these vines which received a treatment is nice and clean!

I hope you will have a nice July 4th weekend. If you travel somewhere, please drive safely.

Wednesday, July 1, 2009

Thunderstorm is coming...

The radar is showing thunderstorms for tonight (now I heard the thunder...); however, in the past few days, there is only one night when the condition was favorable for downy mildew sporulation. Since we are approaching the end of critical period, those of you who has not seen much downy mildew can relax a bit once the 4-5 week window has past. If you are concerned about downy mildew based on your assessment of the vineyard and if the vines are not protected, then you can apply Phosphorus acid or Ridomil products after the rain. (The forecast is showing chances of rains coming later in this week.)

We visited a vineyard at Southern Piedmont AREC yesterday. This vineyard is set to test a relatively low input practice (14-day schedule of mancozeb+sulfur is the backbone). This year, they did not experience extensive rains as Northern part. In addition, they managed the canopy very well. As the result, we could not find major outbreak of disease. It tells you that the importance of canopy management (= air circulation) and the incorporation of weather information in your spray schedule. We will monitor the vineyard and see how it holds toward the harvest.