Walking through the vineyard with the dogs last week, I noticed something alarming. While most of the vineyard is leafing out nicely, there is about a half an acre in the lowest part of the vineyard where the vines are still struggling through bud break. Overall, we had bud break in the rest of the vineyard between March 25th and April 1st. So these vines are lagging almost a month behind.
Some of the lagging vines have a leaf or two on them. But others have no green leaves at all. On those vines, some of the buds are trying to open and others are not. A few dozen vines just look dead. The question, of course, is why. Why are these vines lagging behind, and will their buds ever open? Everything was fine with them at the end of the last growing season. And the grass growing around them is growing the same as the rest of the grass in the vineyard. What happened to hold back and possibly kill these vines?
Bob, Nathan and I have explored several theories. All of the affected vines are in the lowest ground in the vineyard, where water pools during the winter. One explanation could be that all that water leached critical nutrients out of the soil, leaving the vines malnourished. The problem with that theory, though, is that the vines use stored nutrients from the previous year to open their buds and only rely upon soil nutrients once their roots are awake and their leaves are taking in sunlight. If the water had washed away the nutrients, the buds would have still been able to open and it would be the shoots that would be struggling now to survive.
Another possibility is a disease or a pest. So we did a careful inspection. We didn’t see anything of concern above ground. Below ground, vines can be damaged by phylloxera, a tiny insect that feeds on their roots. But we planted grafted vines made up of a French grapevine grafted to an American rootstock that is resistant to phylloxera. And phylloxera doesn’t prevent bud break, it weakens the vine over time. So that can’t be it.
We also thought about bud damage during pruning. But assuming a careless pruner (unlikely given our crew), the damage would have been scattered throughout the vineyard, not concentrated in one spot. Pruning is a social time in the vineyard and we all work together. Nobody goes off and prunes their own section.
The the theory that made the most sense to us was that maybe the cold snap last December killed the unopened buds. I learned in my viticulture classes about winter bud kill. It’s extremely rare here in southern Oregon. But in places like upstate New York and Michigan, where the winters are brutal, it often gets cold enough to kill dormant buds. We dropped down to about 10F for a few days last December and that’s about as low as the temperature can go without killing buds. Is it possible the low part of the vineyard got even colder during that cold snap, cold enough to kill off the buds?
Time to call in an expert. Luckily for us, our neighbor Monya grew in France and she holds a degree in viticulture from a French University. She’s also worked in vineyards and made wine all over the world in all kinds of climates. Now, she and her husband have picked Elkton of all places to settle down and raise their kids and start their own vineyard. Elkton is a tiny town in the middle of nowhere, but when it comes to vineyard expertise, the resources here are literally world-class.
Nathan invited Monya over to take a look. She very methodically went through the affected block, looking at both the green vines and the dormant ones. She inspected leaves and buds through a magnifying glass to check for tiny mites. She even took a few leaves into the lab to view them under the microscope. Nothing explained the lagging vines. Which was good in a way. At least we don’t have mites!
So back to the vineyard we went. Monya collected a few of the still dormant buds and carefully used the pruners to slice one open. And sure enough, it was dead. I have read about dead buds and looked at pictures. But living here, I had never seen one for real. Frozen buds are pretty rare in The Napa Valley as well, where Nathan is from. But Monya has seen them, most recently when she was working for a cold climate vineyard in Russia.
I don’t have the lens or the skill necessary to photograph what she saw when she sliced open the bud. So I found this image on a Rutgers University website. I hope they won’t mind that I’ve borrowed it (with credit). The image shows a cross section of a wine grape bud, which you might recall from a previous post, is actually a compound bud that contains three separate buds. The primary bud (P) opens first, and if all goes well the other two may not open. But if the primary bud dies, the secondary bud will grow. And if the secondary bud dies, the tertiary bud is the final back up. This is a survival strategy for the vine. While the secondary and tertiary buds don’t produce the quality fruit necessary for wine making, they do give the vines multiple options for producing green shoots.
Looking at the photo again, you can see that the secondary and tertiary buds are green. So they are alive. But the primary bud is necrotic, or dead. The brown color is the telltale sign. And that’s what Monya saw in all three buds when she cut open the compound bud from our vineyard.
Like us, Monya believes it did get cold enough in this part of the vineyard last December to kill the buds. Some of the buds died off completely, while other may still have viable secondary or tertiary buds that are trying to open even now. All it takes is just one green shoot to keep the vine alive. Over the summer, that shoot will produce more buds that hopefully will open next spring.
So we are going to watch and wait and hope that at least some of the still dormant buds will open in time. We’re also going to collect leaf samples at bloom and send them to a lab for nutritional analysis. If the soil in that part of the vineyard is deficient, the leaf analysis should tell us. And, we will test a soil sample for pH, or acidity, which can change over time.
The cold snap in December was an extremely unusual event. Marty Tomaselli, who has lived here long enough to know, says the last time it got that cold in Elkton was back in the 1970s! Nothing here is set up to endure that kind of cold. Our water lines froze, our electric meter caught fire, the roads were encased in ice, and without enough snowplows to clear them, the schools were closed for most of a week. Heck, most of Oregon shut down that week. There was nothing we could have done back then to protect the vines. Single digits are far too cold to mitigate with a bonfire and a vineyard fan.
Winter bud kill is just one of those things that can happen in a vineyard. We are fortunate that the impact has been minimal and most of our vines still have a chance to survive. And we are extremely grateful to our neighbor, Monya, for sharing her expertise with us. People like her are why people like us can start vineyards and learn as we go.