This is my third year for my vines and hoping to to get a crop to harvest this year. They look healthy so far and I had been treating with Mancozeb up to this point but stopped because of the pre-harvest interval. So what can I use up to near harvest?
I guess it depends on where you are, the kind of disease pressure you face, and what you’re spraying for. Keep in mind that mancozeb has a PHI of 66 days so if you’ve been spraying it into veraison I think you may have exceeded that. I spray with mancozeb and sulfur for my first six applications then switch to immunox (14 day PHI) and Captan (0 day PHI). Grapes also develop ontogenic resistance to black rot, downy mildew, and powdery mildew somewhere between 4 and 6 weeks after bloom so you won’t have to worry as much about those on your clusters, though you’ll still want to protect the foliage if it’s threatened.
I stopped spraying the mancozeb when I saw the initial bunches start to color change. Most of the crop is still very green. But you bring up an issue that I have not been able to find much information.
1. How do you determine when harvest will be so you can observe the PHi?
2. When do you start counting the number of days of the growth cycle?
I have Marquette and Marechal Foch. The Foch seems to be well behind the Marquette. I have not been able to find any information on how many days the growth cycle runs.
Additionally, we had a late freeze this year in early May. Literally all the chutes fell off. I didn't think there would be any grapes this year, but many of the vines produced new chutes with grapes.
I think 1 will come with time as you keep good records and learn about how the varieties you have grow in your particular vineyard with its climate and conditions. I’m still figuring out what Marquette does in my little vineyard in Virginia. This year the more vigorous vines I allowed to ripen a little fruit saw veraison around July 4 then by July 27 were at 23 Brix and pH 2.8 and the bugs and birds were starting to set in. My Carbernet Franc has not started veraison yet but talking to other growers near me makes me think it will begin in another week or so but every year will be different. The issue with mancozeb isn’t just the PHI but also that you’re limited to 6 applications a year. For me that meant that my last application of mancozeb was the last week of May.
I’m not sure I understand your second question. You should establish a spray schedule based on the disease pressure in your area and different growth milestones, starting when the shoots are 1/2 - 1” long and taking into account bloom, bunch closure, etc. I modified a chart that Virginia Tech put together.
The more I learn about how grapes develop ontogenic resistance to the diseases that are the most troublesome in my area, the more I think I can stop spraying the clusters well in advance of harvest, but the leaves will still need to be protected so they are around to ripen the grapes and store energy for the dormant season.
Thanks for sharing you chart. We had a late freeze in Mid May, lost all chutes, and the vines started over with new chutes. So it looks like my vines are 5 or 6 weeks behind yours. I would be interested in hearing when you are able to harvest your marquette grapes. I have kept good records this year of the progress of the growth and the spray dates. So hoping to get a better understanding of the timing.
I don't really have an good records from last year. The Japanese beetles and bunch rot and birds wiped them out last year. The grapes weren't any larger than pees, nothing worth harvesting. This is the third year for the vines and the grape fruit size looks more like the wine grapes I have seen at a local vineyard.
I actually harvested the Marquette last Monday, July 27 at 23 Brix and 2.81 pH. It would have been nice to harvest at a higher pH but I was starting to see bugs going after them, some bird damage and shriveling berries, and we had a lot of storms forecast so I pulled the trigger. There don’t seem to be a ton of people growing Marquette in Virginia but the few I know of seem to harvest around this time/early August. I’ll be interested in how they do next year as this was only their second season so I only let a few clusters ripen to see what would happen: 3.5 lbs from 17 vines. I just crushed them and put them in the freezer to toss in with my Cabernet Franc when it’s ripe (only just now starting veraison). Next year I should have more of everything and hopefully a pH above 3 as well. I’d like to try a semi-carbonic maceration next year to help with the acid and pH. Look forward to hearing how yours goes.
I’m growing Marquette/Traminette/Seyval near Ann Arbor, MI. I use mancozeb for the first 3-4 sprays, stopping around June 20 (to stay well clear of the 66 day PHI). I then do 1 or 2 sprays of Immunox, then 1 or 2 sprays of captan (fewer sprays if rain is low and I can stretch them out). You have to limit Immunox use to prevent future disease resistance. By late-July I switch to Serenade (organic) and only use this until after harvest. I always get powdery mildew on Marquette in the fall, and treat that with sulfur or stylet oil. Marquette is ready to pick usually between Sept 5-12, depending on the GDD (heat days). I have to net them as soon as veraison starts to prevent bird loss (they will find any gap in the net!!). If I leave them longer, the wasp activity really picks up and they damage the crop.
I have used it without a problem, but I mostly have used the oil instead. I believe AA says that Marquette is slightly sensitive to sulfur. Immunox says it treats PM, but I have not used it for that. Keeping an open canopy that can dry quickly helps.