Peduncle and shatter?
We are in the Coastal Zone of Monterey County, California, typically too cool for good fruit set for pinot noir (300 vines) and chardonnay (100 vines). We had great clusters (number and size) this spring due to some warm weather at the right time when the buds were forming last year, but the last two weeks have seen maybe 10 hours total over 70 degrees. Mostly mid 60s. So shatter, whole clusters, is happening. I'm also seeing the peduncle at the same time drying up and easily breaking off. Is there something else going on that I need to be aware of, or is this typical of shatter?
Monterey County California
It sounds like the typical shatter - is it more than is generally observed each year? It is also called coulure. However, it usually occurs when the temperatures are less than 60 degrees, so that doesn't make sense. It can be caused by the pull of carbohydrates away from the clusters, which causes the drying up of the peduncle and the rachis, and berry drop. So, one suggestion is to tip the shoots when bloom occurs during particularly cool periods to minimize the competition for carbohydrates and help with fruit set.
I hope that this helps - but as long as your nutrition is adequate, then the shatter is most likely due to the cool weather exacerbating the demand for carbohydrates in the vine.
Dr. Olmstead, Thank you so very much for your reply. I've been dealing with coulure and millerandage every year. It's strictly a hobby & occasionally I've had enough good grapes to make some wine.
In 2013 and 2014, we had warm enough spring weather to yield maybe 2 lbs/vine, after four years of almost nothing. This spring, we had many clusters (lots of promise), but cool weather for nearly the entire month of May and essentially a total loss.
I monitor the temperature in the canopy to track the PMI. We had 8 days out of 31 in May with only 2-3 hours reaching 70-71 degrees. My understanding has been that pollination and fertilization require temperatures of 70 to 85, at the right time. The vines are quite healthy, and well pruned, but the 60s are just too cold (with low 50s overnight). I would appreciate any ideas you may have!
I should add that the shatter was more dramatic this year than normal (at least more noticeable, having many promising clusters!), which prompted my initial question. Thank you agian!
Some of the growers in the Puget Sound region of Washington State also deal with cool temperatures during pollination, as well as overall low growing degree day accumulation. They "tent" the fruiting zone so that they can increase the temperature, increase growth and fruit set in their vines.
A professor up in British Columbia has published a few papers on this, and was the basis for their practice -
Impacts of using polyethylene sleeves and wavelength selective mulch in vineyards. I. Effects on air and soil temperatures and degree day accumulation. P. A. Bowen, C. P. Bogdanoff, B. Estergaard. http://pubs.aic.ca/doi/abs/10.4141/P03-093.
This might be an option for your vines, particularly if there is a stretch of cool weather occurring during bloom. Most of the Puget Sound growers just go to Costco or Sam's club and get the large rolls of polyethylene and walk down the row, or have fashioned an applicator that attaches to a 4-wheeler.
I hope this helps!