Showing posts with label GDD. Show all posts
Showing posts with label GDD. Show all posts

Thursday, July 30, 2020

Don't trust your own senses, in determining whether this is a hot summer!

Here's what I just wrote to my fellow grapegrowers in SW WA (and, first, you need to know that Growing Degree Days measure heat which is a proxy for sunshine; growers use GDDs to know how warm their growing season really is):

It's been so hot for the past few days that it seems strange to get this result, but we had a late, cool Spring, and:

I know the high-lo temps for today and tomorrow, so I can calculate GDDs (F; base 50) for Jan 1, 2020 through July 31, 2020, and the total is: 1189. That is the lowest of THE PAST SEVEN YEARS.

Next, I took the 15-day forecast and used that to project all of August, and that adds 604 GDDs, for an Aug 31 total of 1793 (but if the 2nd half of August is cooler than the first half, which is normal for us to see, that 1794 estimate will end up being a bit too high). That is the lowest of the past 3 years (but not the lowest of the past 7 years).

In recent years, September has added about 500 more GDDs (it varies a lot depending whether the rains come early--last year, Sept only added 250 GDDs). So if we get "normal rain return date" (about Sept 21), that might leave us at about 2290 GDDs by Sept 30. That is better than average for this area, if you look at the past 50 years, but due to recent climate change it would also be the second-lowest of the past 7 years.

So I am going to continue dropping fruit now, to help the remainder get fully ripe, just like last year, on all my varieties except the ones that have shown they can ripen a huge load no matter the weather (only some of my modern varieties can do that). If growers let a full crop hang, I predict they may have less-ripe flavors. It's a very difficult decision to make, of course, as each grower has to think about their own fruit quality and income needs. 

Comments welcome,
Kenton
Your Education Committee Chair

Sunday, September 8, 2019

These heavy rains: What's it mean for the 2019 grape harvest?

1. Is this a good or a bad year for grapes, here on the wet (west) side of the Cascade Mountains? That is still hard to say for sure, but there are many large problems facing us grapegrowers now, that we don't see in a year with dry weather all the way to ideal harvest time.

Here are the factors:

a. Weather: If a great year has a long, dry summer, then the weather for grapes is TERRIBLE this year. First, the grapes budded out about two weeks later this year than last, due to a late, cool Spring. (And, even last year, another cool year, the grapes budded out later than normal.) Second, we didn't have enough heat in this short summer to let the grapes catch up, so they stayed behind. Third, these heavy rains we're getting yesterday, today, tomorrow and Tuesday are super-early -- about a week earlier than last year (which was also very early) and three weeks earlier than the end-of-Septembe/early-October rain return date that we grapegrowers hope for. Heavy rain prevents further grape ripening and dilutes the grapes' flavors (the water content rises inside the grape). That can throw the desired sugar/acid balance out of whack. And it can even split the grape, which ruins it.

If you like numbers, look at Growing Degree Days (GDDs), which use temperature as a proxy for sunshine: Through today, my vineyard (Woodland, WA) has had 1,940 GDDs year-to-date, whereas in the warm year of 2015, we saw about 2,100 GDDs through this date -- a huge difference.

b. Grapes' defenses against predation: When it is cloudy or rainy, the birds take it as a signal to come in and eat the grapes. I saw that start up big-time a few days ago. It doesn't take many birds to eat out a good-sized vineyard in just a few days. Even nets don't totally protect the fruit. Also, wasps need to eat sugar before the winter, and they love grapes. Wasps have trouble piercing thick-skinned grapes, but thin-skinned grapes are easy prey. A grape like Riesling can hang into November wtih its tough skin, but a grape like Regent is toast after heavy rains and wasps. Pinot Noir is not very tough, either, and neither are some of my modern varieties.

c. Grapes' defenses against disease: I don't have to spray for fungus because my modern grape varieties are resistant, but a susceptible grape can succumb to fungus during a rainy spell when the farmer can't spray. Grape disease pressure rises very high, with high humidity.

d. Vineyard and grape variety factors: In an average summer, if Fall rains come early, I can have most of my grapes already picked and safely in the winery, because my vineyard has steep South-facing slope (which receives more solar radiation then a flat vineyard), and because my varieties ripen very early. But the grapes budded out so late this year and the rains came back super-early, so I was able to pick only two varieties so far, just before this deluge (half my Leon Millot and all my Labelle). I have many very-early varieties, but they are all way behind, so outside they sit, with my fingers crossed. Surely the most-common vinifera varieties (Pinot Noir, Chardonnay, Pinot Gris) are also way behind, because they ripen long after mine.

All of that sounds pretty bad, for this year.

However, if the grapes survive these rains, it looks like there are still many sunny days probably coming, after next week's two-day return of yet more rains. That is why it's so tough to say, now, whether this is a good or bad grape year here. The big question will be: Does anybody still have healthy grapes, with good flavors, after the rains, birds, wasps, and fungus have all done their worst? I am not very optimistic that most vineyards will do well this year. I know that I will lose a lot of my remaining fruit.

Many grapegrowers put such a heavy spin on late-season rain that they begin to lose credibility. They want you to think it's not so bad, because they have wines to sell. I've heard remarks like, "Oh, we needed some rain, because the grapes were very dry." Maybe, if the vine was so drought-stressed that there was danger the fruit wouldn't ripen. But usually a super-dry summer will result in great fruit, as the plant (pardon my anthropromorphism here) is worried about the drought conditions, and is in fear for its own survival, and tries extra hard to make its grapes the most-delicious-possible so the grape-eating predator will scatter the seeds for the mother plant. Irrigated vineyards might water during the summer, but by about mid-August they shut off the watering, because the fruit is best when it finishes dry. That is the plain truth.

On the hotter, dry side of the Cascades, it is probably still looking good.

This kind of summer makes me very glad that my vineyard is small and I don't need the wines from this year's fruit to be able to pay the bills. And yet, I have to say that the wines I'm already making should turn out good. But overall yield could be quite low this year, and overall quality could also be low, depending on the above factors for each specific location and variety.



(photo credit: Tanzania)



Sunday, August 25, 2013

Venus grapes

I was out checking chemistry at the Rombough Vineyard in Aurora yesterday. Look at these:


Those are Venus grapes: Seedless, large berries in large clusters. They reached 14.9 Brix in Aurora OR (140' elev) on August 24, 2013. They will get a bit riper but are very edible now. Mild pleasant flavor.

That's an early harvest for this area. Everything will be early if the weather pattern holds, though it has been cooler and  more humid of late. We're at 1643 Growing Degree Days YTD, and it's likely we'll top 2000 but unsure by how much. 2100 or 2200 is in reach if it warms back up.

Tuesday, June 18, 2013

2013: A warm start to the vintage, in the Pac Northwest:

Weather Underground is a good source of historical weather info. I use it to check on Growing Degree Days (base 50F), which is a measure of the amount by which the average daily high and low temps exceed 50 degrees F. It's a rough proxy for sunshine, and thus it correlates with grape development and ripeness.

Year to date 2013, we've had 534 GDD's near our place. Compare that this time in 2012 (a warm year for grapes), which was only 381! And in 2011 (a cool, wet year), it was only 216! It's early, but it looks like it may be a warm year, great for grape ripening.

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