Some Notes on Grape Diseases

Yesterday I went to a research vineyard in south MS where we have a few different bunch grape cultivars planted for observation.  The cultivars in the planting include: Herbemont, Miss Blanc, Delicatessen, Blanc du bois, Cynthiana (Norton), Himrod, and one marked “SV12-375”.  SV12-375 should be Villard blanc.  However, with red berries, I believe it to be Villard noir instead (SV 18-315).  At any rate, everyone of them had disease problems.  We have not sprayed to prevent fungus, as I wished to observe what would show up during the year.  Here is what I can report on the four main diseases I observed:

Anthracnose

I found anthracnose on most of the cultivars, but it was especially heavy on Blanc du bois.  In fact, nearly the entire crop was wiped out and the leaves looked terrible.  This disease was also seen on the Villard noir, but nowhere near as devastating as on Blanc du bois.  To learn more about anthracnose on grapes visit this link: http://www.extension.org/pages/31136/anthracnose-on-grapes

Black Rot

Black rot was seen on Herbemont, Blanc du bois, Cynthiana, Delicatessen, and Miss blanc.  Overall the black rot was not severe on Herbemont and Cynthiana, just spotty and mainly on the leaves.  The entire crops of Miss blanc and Blanc du bois were gone, like due to black rot (and perhaps other fungal pathogens working in concert).  For more on black rot see this link: http://www.extension.org/pages/31134/black-rot-of-grapes

Downy Mildew

Perhaps the worst disease was downy mildew.  Herbemont was ate up with it, as was Delicatessen and Himrod.  In the above photo one can clearly see the difference between downy and powdery mildew — downy mildew sporulation is on the underside of the leaf, whereas powdery mildew is on the top of the leaf.  Downy mildew often creates an “oily” or “water-soaked” appearance on the leaf and turns yellow.  For more go here: http://www.extension.org/pages/31526/downy-mildew-of-grapes

Powdery mildew

image:PM on grapes.jpg

Powdery mildew is one of the most devastating diseases of grapes around the world.  And it certainly showed up in our vineyard as well.  It was mainly observed on Herbemont and Villard noir.  The fungus can colonize leaves and fruit, often causing the fruit to split.  The fruit on Herbemont (and there was a lot of fruit) was covered in the fungus, as were the leaves and stems.  The fruit had not yet reached veraison (but was getting close).  I suspect not too much longer and that fruit will be rotting on the vine.  More info on PM is here: http://www.extension.org/pages/31529/powdery-mildew-of-grapes

This year is a complete loss for fruit — and I knew that going in — but I was happy to make some positive observations as well.  The foliage of Miss blanc was clean.  The vine was vigorous and looked great.  The downside was that all the fruit was gone.  With a competent spray schedule this cultivar may have merit.  Also on the positive side was Cynthiana.  Not much disease observed there either.  Some on the leaves, little on the fruit, but overall pretty decent.  The crop load was small, but this could be because of prior neglect (the vines had not been pruned for 5 years or so).  It looked promising.  I also did not see any clear evidence of Pierce’s Disease (http://www.extension.org/pages/33077/pierces-disease) although it is still a little early yet in the summer for that one to manifest in a big way.  I will keep my eyes peeled for it.  At one time there were other cultivars in the planting such as Concord, Crimson, Thompson seedless, etc. but those all died out.  The Himrod and Delicatessen also looked very poor and may be on the way out too.  More updates to come as things progress.

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3 responses

  1. I observed basically the same thing seeing how different varieties would grow without spray. They are all riddled with disease. Anthracnose being the big one and then black rot and so on. If you get varieties with a lot of lubrusca or vinifera you even see issues where they don’t grow when temperatures are high and generally lack vigor in a southern climate. I have tested a lot of them like orlando seedless, daytona etc. that are not listed here as well.

    Only a few varieties showed promise:

    Lake Emerald: minor issues with the roots. It grows very fast in ideal conditions but usually hits a wall at some point and is generally healthy but may not grow as much or may not produce as many grapes. When you dig it up the root ball is smaller than would be expected. So I don’t know it just doesn’t develop good roots (even though it is recommended as a root stock). Sometimes responds weird to the southern climate but overall basically disease free other than really minor mildew on a leaf or two or something extremely minor.

    Caribe: Does well in the tropics. Very tiny amount of anthracnose but not enough to be an issue. Doesn’t need spray.

    Merlan: Not sure about pierce resistance, and may not respond well to high humidity but completely disease free. Similar to lake emerald it might be possible to see a little spot or two somewhere based on what I read about it but I haven’t observed any disease.

    Q21-B: I don’t remember the name exactly. Probably (cabranet sauvignon) x (tillifolia -possibly shuttleworthii-) crossed with Norton. It is similar to Norton in most respects but better adapted to the south. The only issue it has is black rot which only occurs in really hot humid conditions. Has a really strong and healthy root system and very cold tolerant as well.

    The only other noteworthy variety would be orlando seedless. It is completely destroyed by anthracnose but really well adapted in every other way. It does really well in the heat and humidity, roots easily, very vigorous, seems to resist other diseases well. It would be a good parent if crossed with something that has good anthracnose resistance. It is being used extensively as a parent by UF for future crosses. It produces good wine, and has good flavor but the berries are tiny.

    Almost everything else doesn’t stand a chance without spray. Some varieties won’t even do well if sprayed because they don’t respond well to high heat or other issues. They might survive, but not really thrive. I never tested conquistador though.

    Villard blanc will actually fare better than blanc du bois and a lot of other ones in a no spray situation. But probably ten years down the road or so it will eventually decline due to not enough pierce resistance. And all of the french-hybrids respond poorly to high humidity or really wet soil (such as getting cotton root rot). If you live in dry climate (like drier parts of texas) those are the best places for them, like the southwest. Villard blanc and Merlan are the two most disease resistant french hybrids and there has been extensive testing to confirm this.

    • Thanks for your comments Raymond. I have since “moved” some of the cultivars to a different location in Poplarville where we have been able to spray them. Anthracnose is the most significant disease, especially on Blanc du bois. Last year with the prodigious rainfall in the spring we couldn’t control it adequately. Bunch rots showed up later too. Just too much and too frequent rains. Villard blanc did fairly well overall, but I have concerns about its viability. I see problems with it now after 3 seasons and can’t see how it will continue on for another 7. It may surprise me, but I doubt it. I have Lake Emerald which has grown well, without much disease on the plant, but some on the fruit. I haven’t harvested it mainly because I don’t have the time. The cultivar I am currently enamored with is MidSouth. Easy to manage, little disease from open canopy growth habit, loose clusters, intriguing flavor. I have a local winery very interested in using it for blending because of the flavor. Acidity too high and sugar too low for varietal purposes though.. Good eating grape, my favorite. I’d like to try Orlando Seedless, but I want to move away from anything that gets anthracnose as that requires more effort than a “typical” homeowner, hobbyist, small grower will wish to expend.

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