This concord vine in my GH had been growing well so far this season when I spotted this leaf with what looks like some disease on it.
To me it looks like a variant of rust on apple trees. Whatever it is I am concerned because there was a similar outbreak of what looked like the same browning of the leaves last summer.
Does anyone know what this might be, and suggested ways of controlling/eliminating it?
Do you suspect rust fungus or rust mites? Does it have a powdery appearance on its lower leaf surface? Could the leaf distortion be caused be rust mites?
The large splotches and the spotting could be separate issues.
Could it be sulfur burn? Concord vines are listed as to be sulfur sensitive. Sulfur is often used to control rust diseases.
I would think that you are to far north for Pierce’s disease. Probably not black rot either if you have not seen other symptoms.
Thanks @tennessean.
No powdery (or other) stuff on the surface, top or bottom. Don’t see any “bugs” on the leaf but there are a few white flies in the GH. Perhaps rust, but the affected leaves just get these brown patches. There is also some tip die-back at the growing shoots I have noticed recently.
The nearest match I could find is Pierce’s Disease in grapes; which would be unfortunate as there does not seem to any cure for it.
Anyone know anything about Pierce’s?
It looks like that one leaf got burned by something, it doesn’t look like a disease. In general anything I see on only one leaf gets ignored unless its a disease I already know. There are many many strange infrequent things that can happen.
Scott is right, I can’t remember ever seeing grape leaf diseases at this time of year. Around August is when I see them. Mostly powdery mildew or maybe downy mildew.
About all I know offhand about Pierce’s disease is that I am right at the northern edge of the range of it according to the maps. On the average, I have 1 vine a year to die. I just blame it on Pierce’s and plant another. That’s one reason I have as many vines as I do. If they all would die at once, I would get into the Muscadines.
I’d like to think it isn’t Pierce’s, and if it is the mystery is where did it come from, no grapes outdoors for miles and miles. But perhaps since this vine is in a greenhouse it is susceptible to diseases from further S of here. And it could have come to me with the infection.
@scottfsmith it was just one leaf about a week ago when I first posted. Since then I’ve found a few more and a few growing tips which had died back. Pinched them all off. I might have been a freeze (it did get to 18F outside and may have gotten below freezing close to the glazing in the GH). But the worrisome thing for me is there was a big outbreak of something like this last summer which effected maybe half the leaves. I took off the “infected” leaves and started weekly sprays of neem oil and pot bicarb, which seemed to control it last year. (Actually if the spray did control it, then perhaps it isn’t Pierce’s, as the bacterium for that lives in the wood/stem)
Anyway, for now I think I will go back to the neem&bicarb spray. Don’t think it can hurt anything and it seemed to help last year. (I only have the one vine and really want those grapes 
so I will probably over-react just to be cautious)
High salt content in your irrigation water? Having it in a greenhouse is curious to me.
It could be high salt in the irrigation water. I use well water which is quite hard. Probably time for me to test for that…
And I have the concord in a GH, because after 4-5 years of trying them outside, I gave up. Only got 1 bunch of grapes, and the vines eventually died. A bit too harsh (windy and dry in the winter) here.
Being hard and being salty are two quite different things. The only salt ordinarily in well water that damages plants is sodium chloride, table salt, NaCl. Hard water can be very low in table salt. My water is very hard but hardly has any NaCl. In Amarillo the water was salty and would eat up an evaporative cooler in one yr. But it never bothered my plants because it leached out of the soil well enough to not build up. Drainage and leaching are keys to maintaining low salt in soil.
Hmm, it does look like salt damage I have seen pictures of. Have a look at pictures of it in a search engine. Whatever it is I would say its not a disease or insect based on the pattern of damage. It could be some other nutrition issue if not salt.
Thanks. I need to do some careful observation over the next bit of time.
Our last water test (several years old) did not have high levels of Na, but lots of Ca in various forms making the water quite hard.
In viewing grape leaf pics online, no obvious matches but it seems closest to perhaps an Fe deficiency and possibly an issue with water availability. (Water availability may be why it resembles Pierce’s as that clogs the water transport system of the grape) If anything I have been over watering lately, so I think I will try cutting back on watering for a while, and doing a spray of chelated Fe and some seaweed to cover any micro nuts that may be missing.
The pictures of Fe deficiency that I have seen causes iron chlorosis (which is a yellowing) in the entire leaf. Your picture is not like that. I would look for too much of something. I saw somewhere on the web where too much of one mineral was limiting the uptake of another mineral. For the life of me, I can’t find that article again.
It looks like you have plenty of nitrogen. Is your grape vine in a container? Just curious.
By the way, I saw on the other thread where you mentioned that you get 100+mph winds every year. That’s category 2. What are they straight line winds? Its been 14 years since we have anything like that here. Which was a derecho dubbed as Hurricane Elvis by Memphis folks. With that kind of wind I would think that a greenhouse would get blown away.
Sam, @tennessean, the vine is in the ground in the GH. It’s roots have access to a fairly large space (16’x35’) but there are various annuals in there too; but I don’t till or put other plants in within 5’ of the grape.
There are some interactions I am aware of, like excess N limiting Mg and the like, but I don’t see any familiar signs of deficiencies here.
And yes, 100+mph straight line winds, pretty much every winter into spring (which is why my GH has a steel I-Beam running down the middle of it, designed for 135mph). But these winds don’t really come into play inside the GH, at least as long as the glazing stays on.
