Tuesday, July 19, 2011

Late season powdery mildew #2

I have been receiving more than usual number of calls and emails about powdery mildew this year.  It seems that consensus is that it started to show up on clusters last week and just keep going.  We have passed critical time for cluster infection at this point, thus, you may wonder how it happened?  Since it takes 7-10 days to develop symptoms (powdery appearance on the surface, i.e., spores), and it probably takes a few generations prior to the explosive outbreak, thus, the initial infection events probably took about 20-25 day ago when berries are still susceptible.

Management options on on-going powdery mildew infection is limited.  As with other diseases, we do not have real curative or eradication material against powdery mildew.  Also, it is not recommendable to apply protectant fungicides because there will be higher risk of fungicide resistance development; however, as I mentioned in the previous post, there are a few options that can help you out.  All of them requires through coverages of target tissues since they need to contact with powdery mildew pathogen to be effective.  Also, please keep in your mind that none of them can provide near 100% efficacy as a protective fungicide does.

1) Armicarb or Kaligreen or Nutrol: These are potassium bicarbonate materials, and often recommended during this time of the season because its efficacy and an ease of use.

2) Stylet Oil: The rate is 1-2% or 1-2 gal of Stylet Oil/A with 100 gal of water.  It can provide as much (or even better) efficacy against powdery mildew as Armicarb or Kaligreen; however, you will need be aware of some precautions for the usage.  As with any other oil-based materials, there is some compatibility issues, thus, the general recommendation is to apply by itself, and you cannot apply some types of chemicals within a few weeks after oil application.   For example oil and captan can cause phytotoxicity.  In addition, you need to watch the temperature at the time of application.  Furthermore, there was a study showed the ill effect (delayed ripening) by Stylet oil application late in the season, so, it is not recommended to apply more than two times during fruit ripening.  For more detailed information, please visit this site.

3) Oxydate:  It is hydrogen dioxide material. It is recommended to apply back-to-back for three times.  Based on other studies, it does not provide as much efficacy as other two options.

Please make sure to read the label for more detailed information (rates, timing, etc).

We are about to have 3-4 days of high temperature conditions in next few days.  Hopefully these hot days slow down powdery mildew a bit.

Monday, July 11, 2011

Late season downy, Botrytis, and powdery options

I have received several emails and phone calls regards to downy mildew and Botrytis last week.  Also, some people are struggling with powdery mildew.  Here are general options against these diseases at this time of the season.

Downy mildew:  At this point, your berries are out of susceptible period.  However, because of the last minutes rain some of us had about two weeks ago, some locations are experiencing downy on clusters.  Thing is that the infection took place a while ago, and there are not much options available.   For kick-back activity, you can use Ridomil Gold Copper (note: it also have 42-day PHI), or Phosphorous acid materials such as Prophyt or Agri-Fos (0-day PHI).  However, please keep in your mind that kick-back activity is for on-going infection, but not for already established colonies (i.e., if you see downy growth, these are established colonies).  If there are only minor colonies, you may able to keep them contained in the small area by applying these materials.  If you have an outbreak of downy on cluster, you can try Phosphorous acid material mixed with captan.
For protection, most of varieties are within 66 days of harvest, thus, you cannot use any materials contains mancozeb (i.e., Penncozeb, Ridomil Gold MZ).   You can use copper materials (0-day PHI, but please keep in your mind that many wine makers do not want you to use copper close to the harvest), Revus (Revus or Revus Top, 14-day PHI), Ziram (21-day PHI), Captan (0-day PHI), Ranman (30-day PHI), Pristine (14-day PHI) etc.

Botrytis:  It seems that Botrytis found its way to infect some of early season varieties (namely Chardonnay) this year, even if at bloom application was made.  My guess is that it came in soon after the effect of the bloom application was gone (many of us experienced 5 to 10 days of very humid nights in early to mid June, and some of you in the central VA received hail and rains during that time too).  Unfortunately, none of Botrytis materials are curative, thus, you are basically aiming to protect healthy berries.

There are number of Botrytis materials; however, please make sure to read the label carefully.  Some of them are using the same mode of action, even if chemicals and brand names are different.  For example, Switch, Scala, Vangard, Inspire Super contain a chemical with the same mode of action (FRAC code 9).   Thus, a rotation among them are not really a rotation. You can find about a list of FRAC code on my spray guide or VT's PMG (you can download them from the link on the right).

Our regular recommendation is the application at bunch closure (especially for tight cluster varieties, since it will be the last opportunity to deliver chemicals into clusters), and veraison (a study showed high number of spores during verison, and also, sugar level increases --> Botytis likes high sugar content).

Powdery:  As with downy mildew, your berries are probably out from the susceptible period by now.  The infection on clusters you see today probably happened a week or two ago.  Thus, for next year, please make sure to have a good protection program (or make sure your equipment is working properly).

If you have outbreak of powdery on clusters that need to be controlled, you may want to try Potassium bicarbonate products such as Kaligreen or Armicarb.  You need a through coverage to achieve a good efficacy.  The other option is Oxidate which also requires through coverage and 3-time back-to-back application.  Based on previous reports, it seems that Kaligreen or Armicarb provide a little better efficacy than Oxidate.  Please avoid using high or moderate risk materials (i.e., strobies, DMIs, etc) against on-going powdery mildew outbreak.  You do not want to have resistance isolate in your vineyards.

If you successfully protected your berries up to this point, you can probably relax a bit on both downy and powdery mildew.  Just watch the weather and also keep eyes on incoming downy and powdery on young foliages, and make decision based on them.

Disease risks from weekend's rain

I thought I posted it, but apparently I did not!  Winchester area received two showers on 8th (Friday), both events were short, and temperature during the events were about 70F.  The first event was longer (~5 hours, but the amount of precipitation was very small (0.02 inches total).  The second event was short (~3 hours), and it was a thunderstorm.  It was downy mildew infection events, but since previous two days were relatively dry, it might not be a big risk.

Monday, July 4, 2011

Happy 4th! + Disease risks from yesterday's rain and Meeting notice

I hope everybody is having a nice 4th of July. :)

After I posted yesterday, thunderstorm went through Winchester area around 5:50 PM, then there were rains here and there, then the RH was high (>90) until 8:00 AM this morning.  Thus, it was almost 14 hours of estimated wetness event with an average temperature of 70F.  It was Phomopsis, black rot, and downy mildew risk event, and as I noted yesterday, Botrytis can cause infection under this condition as well.

It looks like more thunderstorms are coming our way.  We will see...

Also, there will be a vineyard meeting at Barren Ridge this Wednesday.  If you can make it, please stop by.  We will cover seasonal viticulture and disease management tips.

984 Barrenridge Road, Fishersville, VA 22939-3026


Phone (540) 248 3300

Directions: Take I-64 West.  After crossing Afton Gap at crest of Blue Ridge Mtns. Continue on for 8 miles.  Take Exit 91 and turn right onto Va 285/ State Rt. 603.  Travel 2 miles.  Turn left onto Hwy 250 West and travel 1 mile.  Turn right onto Barren Ridge Road and travel 2.4 miles.  Vineyard and winery will be on your left.

Contact:  Kenner Love, Rappahannock County Cooperative Extension (540) 675-3619

Sunday, July 3, 2011

Disease risks from today's rain and Botrytis reminder

Winchester area received rains this morning from around 2:30AM until 4:00AM.  Then the RH was high (>90%) until 8:30AM or so.  Thus, it accounted for 6 hours of estimated wetness with an average temperature of 70F.  It was Phomopsis, black rot, and downy mildew risk event.  We are about to exit from critical period for berry infection by black rot, downy mildew, and powdery mildew. 

I just finished my second cover after bloom for my trials yesterday (just in time for the rain :) ).  There are many powdery mildews and a hint of downy in my vineyards.  I hope that you have clean clusters up until this point.  After this critical period, you can relax a bit. 

Also, although it typically requires a longer wetness event in the field, Botrytis can cause infection under the same condition as we seen today.  Probably because of humid nights we experienced in the last two weeks, I have already seen development of Botrytis on our Chardonnay clusters.  Plus, I have heard from others that they have also seen Botrytis here and there.  As for the management, it is important to protect clusters at bunch closure because this is the last opportunity to deliver the material inside of the cluster.  This is especially true for tight-cluster varieties like Chardonnay, which was at bunch closure stage at our station when I checked yesterday.  Then it is also recommended to protect at veraison because there are many spores in the are around that time of the season.  Botrytis can cause diseases on many different hosts including Strawberry and onion, thus, there are many spores floating around the air, but if it infects berries, the source of inoculum will become within a canopy or within a vineyard, and as you can imagine, the risk of disease will be high.