Hi all,

There seems to be some species of grape growing wild in my backyard. This is our first year here, so trying to figure out what's going on. The grape plant originates in an empty lot next door and seems to be very old, as it is MASSIVE and very sprawling. Earlier this year, we built a small structure for the vines to crawl onto and we were very (naively) excited to harvest grapes at the end of the summer.

Around early May, our grapevine looked perfect - tons of tiny baby grape clusters and little pink leaves everywhere! However, by the end of May and through June, every single grape cluster turned dry and black and disappeared.

Is there any hope of reviving this for next year? How can I tell if this is a bug problem or a disease problem? The weird thing is that the leaves look fantastic still - the plant itself looks very healthy, but every single grape cluster died very early.

Posting some pictures here to help explain the problem! Would love any advice or feedback on this. Thanks so much!!!

(BTW - North Jersey here.)







(This is an early photo when the grape clusters were first coming in)

From the looks of it this is Riverbank grape (Vitis riparia). And "your" problem is Black rot of grapes.

Honestly it's extremely hard to control it without full access to the plant: the first measure is sanitation, meaning throughly cleaning the ground from fallen leaves and especially eliminating all "mummies", meaning the affected grapes. The latter are a major sources of fungal spores and must be eliminated to reduce the amount of spores that will be released next year. This residue must be destroyed.
There are fungicides that will help keep manage Black rot but, again, since you have no full access to the plant I don't feel like suggesting wasting money to buy anything.

Thanks so much @ElPolloDIablo! That makes sense.

We also purchased 3 new grape plants this spring and planted them in the ground near the existing grapes. At the end of this summer, we are thinking our best bet is to remove the old vine and allow the new grapes to grow up the trellis. Is there anything you recommend to prevent the black rot from spreading to our new plants, other than removing the mummies?

Remove the mummies, in the fall rake all fallen leaves and if any are left on the vine, rip them off: dispose of this debris by burning or burying it deep, do not put it in the compost heap.
Next year, when your vines have started to actively grow, you will need to treat them with a Ziram- or Mancozeb-based fungicide: once when there's enough foliage, and another time when the grapes are starting to develop.

Unfortunately Black rot is not merely native to large areas of the US, but native vines are far more resistant than Vitis vinifera and its hybrids, and so they may act as disease reservoirs: that's why these practices should be followed every year.

Thanks @ElPolloDiablo! Really appreciate your help. Sorry for my slow reply, I'm not quick with forums!

I think we will follow your suggestions and give this plant one more try next summer. I am looking at the grapes now and do not see anymore of the mummies - I guess they've either fallen off and/or disintegrated? I didn't act quick enough!

A couple more questions- would burning the leaves in the fall release disease into the air and affect other plants? Also, I'm noticing some raised pink bumps on some leaves, is this the same disease or something else? It's only on a few of the leaves, but not sure if it will spread.

Thanks again so much!!

Burning is the best way to dispose of contaminated plant material. I have an "incenerator" for the job: an old oil drum with a few holes at on the side bottom. Failing that the good old burn pit (a hole in the ground) will do just fine.