Using growing degree days to forecast harvest

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wood1954

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Last year I harvested my Marquette at 1987 GDDs on September 5 and this year it’s been so cool we are about 120 GDDs behind last year with the long term forecast to be in the 70s. Looks like I’ll be battling the bugs till late September waiting till around September 20 maybe. I wonder if there is a calculator that figures in solar radiation as well.
 
but it would be nice to know when the harvest date will be to line up help, get the crusher etc.

To estimate harvest date: Graph your Brix versus TA and Brix versus pH based on days.

That is:

In a graph, put day you sample on the horizontal axis. On the left vertical axis, plot Brix. On the right vertical axis plot TA.

Then in another graph, also day sampled is the horizontal axis, plot Brix on the left and pH on the right (but plot pH declining --- that pH 2 at the top, pH 4 at the bottom).

As you get data you can start to see where the two lines (Brix and TA or Brix and pH) will cross by date. Harvest time is nearest the estimated point where these lines will cross.

Caveat: If TA or pH gets too out of line for a good wine, harvest before they do, no matter what graph says or what the Brix is.

Also check your Brix * pH^2 (Brix times pH squared). Harvest when it is 200 for whites, 260 for reds.

Hope this helps.
 
To estimate harvest date: Graph your Brix versus TA and Brix versus pH based on days.

That is:

In a graph, put day you sample on the horizontal axis. On the left vertical axis, plot Brix. On the right vertical axis plot TA.

Then in another graph, also day sampled is the horizontal axis, plot Brix on the left and pH on the right (but plot pH declining --- that pH 2 at the top, pH 4 at the bottom).

As you get data you can start to see where the two lines (Brix and TA or Brix and pH) will cross by date. Harvest time is nearest the estimated point where these lines will cross.

Caveat: If TA or pH gets too out of line for a good wine, harvest before they do, no matter what graph says or what the Brix is.

Also check your Brix * pH^2 (Brix times pH squared). Harvest when it is 200 for whites, 260 for reds.

Hope this helps.
just checked my grapes, they are at 213 by your formula, I think next week will be right in line with your formula, thanks, ph is 3.1 and brix is 22 with 3 days of rain and then 4 days of sun forecasted they should be perfect.
 

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