Early Powdery Mildew

[VictorV]

Hi Everyone
I am located in Southwest Idaho in the Sunnyslope region. I have 90 Tempranillo, 90 Chardonnay and 130 Cab Franc vines. The Chard and Tempranillo are 7 years
old and the Cab Franc is 5 years old. This year I'm running into an extreme outbreak of Powdery Mildew. I seems really early. For the last 2 years we have had
unusually wet Springs. Last year the PM was so bad that we lost most of the Chard and Tempranillo. This was due to me not taking care of the vineyard as I should.
Read: not enough spraying.

This year I've been diligent about spraying micronized sulfur using my homemade air-blast sprayer. Once I saw the first signs of PM I sprayed with Kaligreen.
Almost the entire Chard block is destroyed since spraying did not slow down the PM. I cut off the shoots/spurs below where I saw PM from last year. It was a sickening process. There is some PM
in the Tempranillo and Cab Franc but not nearly as bad.

It's my understanding that PM can overwinter on the spurs so I'm considering just cutting off the cordons and creating new ones from the shoots (suckers) on
the trunk.

Is that a reasonable approach?

Victor

 

[wood1954]

i would spray liquid lime sulfur heavily on all vines, the entire vine just before bud swell.

 

[Neb Farmer]

You are finding out what I found out years ago...powdery mildew will wipe out your grapes! The Armicarb or Kaligreen to put the PM in check was recommended to me by a friend who has a large commercial winery/vineyard, and it works. But you still have to keep the sulphur spray going....which for me is at least once every two weeks. if it rains a lot I will shorten that up a bit. If it's too hot...well, don't burn your vines...wait until it cools a bit.
I spray sulphur before bud-break, after bud break, every two weeks until the grapes flower, then I wait until after they are done doing that. THEN back to every two weeks. AFTER harvest...hit them again before winter sets in...then I relax through deep winter.
Rinse and repeat

 

[VictorV]

Great advice. I probably should have sprayed earlier in the season. Fortunately I have a couple of other varietals
so all is not lost. I was planning to replace my Tempranillo next year since it's not growing that well. The vines
are vigorous but I lose a couple each year and some only push a few shoots. I was thinking about replacing
with Syrah but it's equally susceptible to PM. I'm also considering replacing the Chard with Pinot Gris since
it's naturally resistant to PM. I discovered that there are some hybrids that are created specifically to
resist PM. A white grape called "Felicia" looks interesting but I can't find anywhere that sells vines or even
anyone that sells wine made from it so I can give it a taste.

The average humidity was:
May 2024 45%
June 2024 60%
July 2024 22%

 

[Snafflebit]

Wow. That sounds like a terrible case of PM. Sulfur spray is good for preventing powdery mildew, but a full blown case will not be stopped with sulfur. Stronger measures are needed to stop active PM. I spray down all the surfaces when I pass through the vineyard, trunk, cordons, endposts. That keeps the latent spores less active.

 

[VictorV]

Wow. That sounds like a terrible case of PM. Sulfur spray is good for preventing powdery mildew, but a full blown case will not be stopped with sulfur. Stronger measures are needed to stop active PM. I spray down all the surfaces when I pass through the vineyard, trunk, cordons, endposts. That keeps the latent spores less active.

Good point. I am going to spray the ground as well.

 

[Sage]

My experience, SE WA, if you see PM, it's already to late.

A super concentrated lime sulfur when the leaves fall off and again in early spring before buds Start swelling. Light sulfur when leaves are out. Alternate chemicals after that.

I also spray the ground (bugs crawling up bring it) and surrounding weeds (out as far as my sprayer will go). There's one specifically that seems to be a host.

 

[Hazelemere]

Powdery Mildew spray - best one I've seen and I'll explain why in a minute:

~2/3 cup of powdered sulphur e.g. Kumulus S
~2/3 cup of potassium bicarbonate
~ 1 cup of insecticidal soap (e.g. anything containing the potassium salts of fatty acids - e.g. Later's Trounce)

2 gallons of water.

1. de-leaf near any cluster
2. spray the fruit clusters first , soaking them
3. then spray the leaves and canes
4. spray the fruit again

Try to spray when you have no rain in the forecast for 48 hours

Why this cocktail works:

1. mildew repels water because it is hydrophobic (hates water)
2. insecticidal soap wets mildew because it is semi-hydrophobic on one part of its molecule i.e. the fatty acid part.
3. mildew hates potassium bicarbonate because it kills mildew spores.
4. potassium bicarbonate can stick to mildew spores if it has a semi-hydrophobic carrier like insecticidal soap.
5. sulphur can stick to mildew spores to kill them if it has a semi-hydrophobic carrier like insecticidal soap.

Bottom line - if you don't add soap to mildew spray it won't work!