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:
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 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
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 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.