What is this leaf disease?

[Snafflebit]

This is Cabernet Sauvignon in a vineyard with known eutypa. There are sections of the vineyard where some vines, after three years, canes never grow past 2 feet long. The overall plant is stunted. On other vines that are growing well, I am finding some spurs have canes where the leaves are turning red and a bit curled. I do not have experience with viruses, but I am beginning to suspect that virus is playing a part in the poor growth of this vineyard. I have blamed shallow soil in the past. Maybe I need to start pulling vines.

Opinions?

 

[David Violante]

Did you find out what this is? I’m curious to know.

 

[FlamingoEmporium]

Sure looks like you’ve got some insect infestation

 

[Snafflebit]

Hmm. Insects never crossed my mind. I will bring a magnifying lens to the vineyard next time.

From my research, leaves changing to red like this could be due to a number of causes. It is isolated to spurs. I'm just puzzled about the general lack of vigor in portions of the vinyard.

 

[BigH]

Consider submitting leaves for petiole analysis. I would submit two samples

1. Leaves collected from vines with good vigor
2. Leaves collect from vines with low vigor

My hunch is that the discoloration is potassium deficiency

H

 

[wood1954]

looks like potassium deficiency to me to. Along with a petiole sample do a soil test. Grapes use a lot of potassium

 

[FlamingoEmporium]

Or possibly this based on your photo

 

[wood1954]

That does look like it, bad news for sure

 

[David Violante]

I very unfortunately have a feeling you may be right.
https://grapes.extension.org/grape-leafroll-disease/

 

[FlamingoEmporium]

 

[Snafflebit]

I suspect Leafroll virus is present. And I also suspect the virus operates latently, slowing the growth of the plant until stress causes the vine to display these symptoms of curled red leaves.

I have replanted ~30 vines from a clean vine program. If those new vines grow vigorously, that will be another clue.

I ordered a petiole analysis of the good and bad portions of the vineyard and the main difference found in the weak vines was nitrogen deficency. But I fertilized and did not see those vines bounce back to life as I had hoped.

 

[Snafflebit]

I received the soil sample test, for the curious. I need to go back and check prior petiole analysis but the soil test is confirming the low B and N. I am seeing short internodes indicative of B deficiency on the newly planted Merlot vines.

I will sprinkle some ammonium nitrate around the weak vines after harvest. Need to go back to my notes and calculate weight of N in ammonium nitrate. I am seeing more signs of leafroll develop on different vines as well.

 

[dwhill40]

I had one Cab Vine of many turn red and die after around three years while under stress. I came to the conclusion it was a virus from the nursery. All vines around it were fine.

 

[Snafflebit]

I had one Cab Vine of many turn red and die after around three years while under stress. I came to the conclusion it was a virus from the nursery. All vines around it were fine.

What worries me is that most likely all these vines come from the same grafting material. Even if it is not presenting on the vines currently I will bet that all of the original vines have the leafroll virus. Now I plan to look more carefully for mealybugs which are a vector for the virus.

 

[David Violante]

Thank you for updating us about what you found and what you're planning to do, it is super helpful. Sorry you're going through this.