Solving longstanding grape problems - Ask Extension
I built a grape arbor behind my house in Catonsville several decades ago in order to dine outdoors under the vines, for which it has succeeded admirab...
Knowledgebase
Solving longstanding grape problems #929755
Asked April 27, 2026, 11:08 AM EDT
I built a grape arbor behind my house in Catonsville several decades ago in order to dine outdoors under the vines, for which it has succeeded admirably. I was hoping to also raise table grapes so I planted 6 different varieties of seedless grapes (Concord Seedless, Mars, Reliance, Canadice, Himrod, and Suffolk Red), two vines of each variety. A large balck walnut (which came down last year) was growing about 20 feet away, so I excavated the soil to a depth and width of about 3' along the walnut side of the arbor (where 7 of the vines were to grow), lined the sides of the trench with plastic and the bottom with root-prevention fabric, and refilled the trench (can't remember what I used for soil, but I'm almost sure it wouldn't have been the original soil). The other 5 vines were planted in a sort of planter trench along the other side of the arbor, which I think was similarly lined, except one side was pressure treated wood, and I know the soil was a mixture of home depot topsoil, sand, compost, and probably subsoil from a different part of our property, far from the walnut.
The vines don't get as much air movement and sun as I would like, and for years, the fruit succumbed to black rot in spite of my trying to control it with flowable copper fungicide. I finally hired a tree spraying service to spray it 3 times a year with fungicide and that solved the black rot problem, but the fruit still always falls off at about veraison. There's also bird and squirrel predation but I don't think that is yet a major issue as I have yet to harvest a single grape.
In recent years, the vines have died off, one by one, until there is only one Concord Seedless still growing, and one other variety that is about to die. I suspect the cause of the vine death was underwatering during drought.
I have just had the soil tested on one side of the arbor (unfortunately not on the side where the remaining vine is located) but I don't know how to interpret the results. They seem to say the soil is nutrient starved (low N, P, K, S, B), oversupplied with Ca, Mn, and Cu, and acidic. But I would think my problem, especially for the remaining seemingly healthy vine, must be a disease of some kind.
I am now ready to replant vines, if there is any hope of actually harvesting grapes, but I clearly need help to identify what I have been doing wrong. I don't expect that the necessary help can come from online information--I think I need someone to come by and inspect the site and how things are going at several times during the year, especially when fruit starts dropping prematurely. Is there anyone you can put me in touch with who might help?
Baltimore County Maryland
Expert Response
Limited root space from the original trench setup likely played a role, and juglone from the walnut was probably not a major factor (juglone can persist in the soil for a few years after a live tree is gone). Yes, cumulative drought stress was also probably a contributing factor if the vines were not monitored for watering needs and irrigated as the weather dictated. Good air circulation is very important for grape vine health and discouraging fruit infections, and the plants also need to receive full sun (6-8 or more hours of direct light in summer), which it sounds like they may not have been given how close the mature walnut had been.
You can share a file or scan of the soil test report here (attach it to your reply) and we can help interpret the information. It would be unusual for several major nutrients to be low enough to cause deficiencies in the plant, and "excesses" of some minerals like calcium are common and aren't a problem. (The "excessive" category on lab nutrient measurement charts doesn't mean the element needs to be reduced, but merely that adding more via fertilizer will not benefit roots since the soil already contains more than they need of that element/nutrient.)
Too much copper could be a problem, as it can build up to root-toxic levels in the soil from years of fungicide applications (unless there's another source or pollution as the cause), which is why copper-based fungicide sprays tend to have instructions on the label regarding a limit on how many applications can be made per year.
Our Growing Grapes in a Home Garden page has all the information HGIC has on home grape cultivation and troubleshooting. While some diseases (like Black Rot in this case) can be quite widespread and common, many plant disorders arise from stress due to their growing conditions, be that root moisture extremes (too dry or too wet at some point) or soil compaction (which deprives roots of enough oxygen), high heat (especially if it's reflected/radiated off of any nearby pavement, brick, walls, solid fences, etc.), root exposure to cold (if a hardy plant is growing in a container or narrow raised bed, for instance), too much shade, or foliage/branch crowding from overgrowth or a need for pruning.
We don't have information to share on experts to hire, as Extension doesn't collect information on what services various landscapers or arborists offer, nor do we recommend particular businesses. Last we checked, there seemed to be very few landscaping or IPM companies that have expertise with pruning and managing fruit plants (trees, shrubs, vines), but you may need to ask around. UMD Extension Agent Joe Fiola is a viticulture specialist, but his area of expertise is commercial grape production, and home grape growing might have different challenges and constraints. You can reach out to him via the email in the linked page if you'd like to see what feedback he has.
Miri
You can share a file or scan of the soil test report here (attach it to your reply) and we can help interpret the information. It would be unusual for several major nutrients to be low enough to cause deficiencies in the plant, and "excesses" of some minerals like calcium are common and aren't a problem. (The "excessive" category on lab nutrient measurement charts doesn't mean the element needs to be reduced, but merely that adding more via fertilizer will not benefit roots since the soil already contains more than they need of that element/nutrient.)
Too much copper could be a problem, as it can build up to root-toxic levels in the soil from years of fungicide applications (unless there's another source or pollution as the cause), which is why copper-based fungicide sprays tend to have instructions on the label regarding a limit on how many applications can be made per year.
Our Growing Grapes in a Home Garden page has all the information HGIC has on home grape cultivation and troubleshooting. While some diseases (like Black Rot in this case) can be quite widespread and common, many plant disorders arise from stress due to their growing conditions, be that root moisture extremes (too dry or too wet at some point) or soil compaction (which deprives roots of enough oxygen), high heat (especially if it's reflected/radiated off of any nearby pavement, brick, walls, solid fences, etc.), root exposure to cold (if a hardy plant is growing in a container or narrow raised bed, for instance), too much shade, or foliage/branch crowding from overgrowth or a need for pruning.
We don't have information to share on experts to hire, as Extension doesn't collect information on what services various landscapers or arborists offer, nor do we recommend particular businesses. Last we checked, there seemed to be very few landscaping or IPM companies that have expertise with pruning and managing fruit plants (trees, shrubs, vines), but you may need to ask around. UMD Extension Agent Joe Fiola is a viticulture specialist, but his area of expertise is commercial grape production, and home grape growing might have different challenges and constraints. You can reach out to him via the email in the linked page if you'd like to see what feedback he has.
Miri
