Dark spots on some PS clusters, but not on CS clusters?

[we5inelgr]

Hi all,

Any ideas what this might be (the dark/black spots)?

This has appeared in the last week (since I last checked the vines).

It appears only on a few Petite Sirah clusters (out of 16 vines), and not on any Cabernet Sauvignon (out of 8 vines). These are 3rd year vines, the rows are very closely spaced.

We do have leafhoppers abound, but I'm thinking it's not to the point of needing remediation yet.

Also, we did have a recent heat streak, upwards of 105 - 107 for several days (in the north part of Lodi AVA).

Thoughts on the black spots?

 

[balatonwine]

From the grapes and speckled leaf damage looks like black rot. More information and photos to compare at :

http://entoweb.okstate.edu/ddd/diseases/blackrot.htm

https://commons.m.wikimedia.org/wiki/File:Guignardia_bidwellii_(black_rot)_on_grape_1.jpg

 

[grapeman]

I agree that it looks like Black Rot. Did you spray the vines at all this year and if so what was used? It is best to try to keep this out of your vines even when young because it is hard to get rid of once established.

 

[we5inelgr]

Thank you both for your replies.

I did not spray the vines with anything this year.

There are approximately 9 clusters affected. What's the best remedy at this point?

Since there are so few involved, could I simply cut out the individually damaged berries? I'd like to save as much of my minuscule amount of fruit as possible.

Or would it be better to cut off each affected cluster?

In either case, I should then spray with either myclobutanil (Immunox) and / or captan and / or copper, and keep reapplying as per the directions. Correct?

One other thing, once that fungicide is applied, prior to harvest, should I spray the vines/clusters with water to remove as much of it as possible so it doesn't wind up in the must? Or, is that nothing to worry about??

Thanks again.

 

[user 36973]

The berries will rot and fall off on their own. Some may hang on as mummies that you can either remove at harvest or just send in with your crush.

Captan works well for black rot and it can be applied up to the day of harvest. There is no need to spray off the residual pesticide. Captan wants the spray pH to be acidic, so depending on your water supply you may need to add some acidic additive to the tank.

You should read&follow the label for the application amount to grapes. The reapplication interval is something like 10-14 days. Be sure to spray frequently until veraison to guard against black rot.

 

[we5inelgr]

Thanks again all for the replies and suggestions. I appreciate it!

I had also contacted UC Davis's Plant Science division regarding their condition, and their response was:

The foliar symptoms appear to be leafhopper damage.
http://ipm.ucanr.edu...r302300111.html

The cluster symptoms can either be Sour Rot or Botrytis Bunch Rot.
http://ipm.ucanr.edu...1.html#SYMPTOMS
http://ipm.ucanr.edu...r302100111.html

This makes sense to me now that I think about it more. I mentioned leaf hoppers in the IP because we noticed them last year (2nd year leaf) and the leaves looked the same last year (with no fruit, as we dropped it all) as this year. They said not to worry about the leaves too much unless...essentially, it gets roughly twice as bad, then intervene. Our region is known to be prone to leafhopper issues.

Regarding the damage on the berries, bunch rot makes sense as well because we are only seeing this on the Petite Sirah grapes and not on the Cab Sauv.

My initial thought before my inquiries was black rot as well...just based on what the affected berries look like. However, after more research and responses, it seems it's more likely bunch rot.

In either case, I'm going to try out Serenade Fungicide since it's has a very wide range of pests controlled, including Botrytis, Black Rot and Powdery Mildew (among many others), it's compatible with Copper, Sulfur and other fungicides/insecticides and has resistance control.

We'll see.

Thanks again!

 

[balatonwine]

Thank you both for your replies.

Of course. Happy to try to help.

Regarding the damage on the berries, bunch rot makes sense

UC Davis: a great resource.

That being said....

I am surprised by these suggestions from Davis. Sour rot (which is a catch all term for many different fungus species that can cause problems in the summer) and Botrytis, in their classical forms, usually occur later in the year. Especially during or after veraison. Some sour rot can look like the photos, but I have never seen this on a grape in June as there usually needs to be more sugar in the grapes to sustain sour rot. And Botrytis looks completely different in its classical form -- the entire berry changes color "at once", not just from one side like yours and the berries tend to keep their form early in the disease, then just shrivel. And Botrytis needs moisture, either spring and summer rains or fog. Unlikely conditions in Lodi unless they are artificially caused from (often overhead) irrigation. Gray rot (the malignant form of Botrytis) can occur from one side and spread, but that needs even more moisture. I have summer rains and have had sour rot, Botrytis and gray rot. Also have seen black rot. So, even though disease ID from a photo alone is risky at best and very prone to false diagnosis, and at the risk of disagreeing with UC Davis, I still say your issue looks far more like black rot to me. Or, maybe, no disease at all but rather.... sun burn (which given the temps you quoted, makes that a possible option too).


That being said.... Davis may be aware of forms of sour rot or Botrytis that do attack grapes in June like this in California that is of a "non classical time and form" I am not aware of (and thus would make me wrong in disease ID, of course).

The only way to know exactly what you have is to get the affected berries analyzed.

only seeing this on the Petite Sirah grapes and not on the Cab Sauv.

Only noticing the issues on the PS may be very relevant, indicative and very useful in getting to a disease diagnosis. But that is only one possibility. Since you only have a few clusters affected, you may have small sample size effects. For example, the appearance that only the PS was affected may be due to micro-environment factors in those vines alone which, purely by chance, happened to be PS vines. In other words, a small sample size may be giving false conclusions if the variety affected is really relevant or not.

I did not spray the vines with anything this year.

It is extremely difficult to grow Vinifera reliably without spraying. One can of course avoid spraying until disease pressures require it, rather than following a fixed schedule, but that is simply a trade off between costs and risk which large vineyards can benefit (because saving many thousands of dollars by not having to spray even once less a season is worth the risk of some loss due to fungus). Small vineyards are often better off following a schedule to reduce risk of lost crop (which can be more expensive than the cost of spraying), and thus optimize success.

In either case, I'm going to try out Serenade Fungicide

A good organic option for all around fungal control. But if this is in fact either sour rot or Botrytis then JMS Stylet oil is a far better option for theses specific diseases.

Also, some canopy management is also a good idea before spraying to ensure you get the fungicide on the grapes.