California Dept. of Water Resources climatologist Michael Anderson kicked off the meeting by attempting to answer the question: "Is the Drought over in California?" The answer is "no", since, even with the rainfall we've received so far, we are not yet seeing near-average run-off accumulating in our reservoirs. This is the result of 4 years of drought and what it takes to actually refill soil profiles enough to accumulate run-off. Michael expects the current El Nino to continue to kick in strong, especially in February, with above average precipitation expected. The freezing elevation level is going to be a key component of whether we accumulate enough snowpack to alleviate our drought in 2016.
Amos Naor, a researcher from the Golan Research Institute in Israel, discussed why plant based stress measurements (stem water potential (SWP) measurements obtained with a pressure chamber) are valuable even when we have soil based sensors and ET0 information. His research in apples, nectarine and pear have shown that the pressure chamber measurements are much less variable than those obtained by dendrometers or tensiometers; and SWP measurements respond more quickly to changes in irrigation regimes, giving the user quicker feedback. Soil moisture variability can be quite large, especially in drip irrigated fields. But the pressure chamber measurements are useless, Naor said, without an established threshold for when growers should use the information to irrigate-this is the key and one I hope to work with foothill grape growers to establish for their blocks. Naor also found that apple crop load can also effect stem water potential measurements-the higher the crop load, the more stressed. I'm uncertain if research has shown this is also true for grapes.
Ken Shackel, UC Davis Plant Science professor and recognized "father" of SWP measurements, described how much
Several speakers addressed irrigation water quality, especially with regards to salinity, an issue that, thankfully, foothill growers don't have to deal with. A number of techniques and models used to estimate and measure soil properties affecting soil water infiltration were discussed. The Israelis have found treated wastewater a valuable and effective water resource, although long term use of wastewater presents challenges due to soil degradation.
The meeting concluded with several grower panels, organized by commodity. Susan Farrington, of Villa Toscano winery and vineyard located in Amador County, accepted my invitation to participate in the wine and table grape grower panel. Susan and her team have experimented this past year with using the pressure chamber, and also use neutron probe soil moisture measurements to make irrigation decisions. Like many foothill growers, they are plagued by problems of iron in their water. After years of sending crews in to change drippers, Villa Toscano is installing a chemical injection system to help keep the iron in solution and hopefully improve their irrigation system's distribution uniformity. Irrigation system distribution uniformity is critical for irrigation efficiency, and is a topic we will revisit in the future. Stay tuned!
The press of the recent resurgence of Pierce's Disease (PD) in North Coast grown grapevines has gotten some foothill grower's attention. But I have never seen a case of PD in grapes grown here. Why? We think that grapevines grown in the colder climate of the foothills benefit from a little understood phenomenon called "cold curing". What is this "cold curing"? The idea is that freezing temperatures cause vine stress that triggers an increase of some phenolic compounds in the xylem, or water conducting tissue. PD is a disease caused by the bacterium Xylella fastidiosa that resides in the xylem. But in cold-cured vines, we think the increased levels of xylem phenolics interfere with the growth of the Xylella bacterium such that disease
Cold curing phenomenon has been studied by the late UC Davis plant pathologist Bruce Kirkpatrick, who contributed much to the science of plant diseases like PD. Bruce, along with Richard Bostock (UCD Plant Pathology) and Andy Waterhouse (UCD Vit and Enology) did work back in 2009 to try to identify the compounds in grape xylem sap responsible for cold curing. That work, funded by the American Vineyard Foundation, was continued in 2010 by Waterhouse, visiting scholar Blandine Cretin, and Mauri Anderson, who works in Andy's lab. I collaborated for a part of the study by locating El Dorado growers to provide five "cold" vineyard sites for comparison (same variety, clone and rootstock) with warmer climate sites in Yolo county that were also sampled. We sampled the canes of vines seasonally, and the Waterhouse lab analyzed the cane xylem sap for phenolic compounds. We looked at Cabernet Sauvignon, Barbera, Pinot Noir, Petite Sirah, Chardonnay and Merlot. The Waterhouse group focused on the 'flavonol' group of phenolics, and found that indeed, the vines grown in colder El Dorado county had 50-120% higher yearly concentration of flavonols than their warmer counterparts grown in Yolo, as reported in a poster presented at the American Society for Enology and Viticulture (ASEV) conference in 2012 (Anderson et al. 2012). Unfortunately, this work was not funded further, so the exact mechanism of cold-curing remains unknown. Interestingly, the current resurgence of PD in the North Coast region is thought to be associated with last season's mild winter temperatures-affecting either the vectors and/or the growth of Xylella.
A few of you growers out there have told me in the past "Lynn, if you want it to rain, hold a field meeting!"
So it is in this spirit that my very first blog post forecast a warm winter right before the major snow dump in the Sierra over the holidays! Indeed the Department of Water Resource's (DWR) California Data Exchange Center (CDEC), my go-to site for up to the minute hydrological information, shows the latest snow data for the American River Basin range sites at 52 to 67 inches of snow! This includes the snow stations at upper and lower Carson Pass, Aloha and Echo lakes, and Tamarack flat. The snow currently has an 18-30% water content and is at 31-60% (depending on the location) of April 1 historic records. According to the CDEC, the April 1 historic average is based on measurements from 1951-2000.
A little closer to home, all of that snow in the Sierra amounted to a good drenching of rain to ring in the New Year. The following stations recorded December rainfall amounts:
Camino CIMIS: 7.41in.
Diamond Springs CIMIS: 6.99 in.
Plymouth CIMIS: 6.49 in.
And our PMI stations recorded December rainfall totals:
Lava Cap PMI: 9.56 in.
Fairplay PMI: 5.8 in.
Amador Eagle: 6.16 in.
Amador Renwood: 5.47 in.
Calaveras Ironstone: 10.17 in. (Wow! this one surprised me, as Calaveras often has lower precip. than further North).
A very good start to the new year. Let's hope the cold weather sticks around.
In years past, I've collaborated with several local Christmas tree growers and Pacific
Merry Christmas and Happy Holidays everyone!
As we move into winter after four years of drought, all eyes are on what weather we can expect and how it may impact Sierra foothill growers next spring. Sources for foothill weather information include the CIMIS (California Irrigation Management Information System) stations, which provide detailed weather information including temperature, precipitation, reference ET, soil temperatures and wind speeds; and the PMI (Powdery mildew index) stations, which provide limited data such as canopy temperatures-used to calculate the grape powdery mildew index- and precipitation.
Here in the foothills we have 3 active CIMIS stations: Camino #13, Diamond Springs #228 (both in El Dorado County) and Plymouth #227 (Amador County). Typically, the Camino station receives the most precipitation, and the precipitation decreases as you move south. CIMIS data can be directly accessed via the CIMIS website (login set up is free but required), or you can access CIMIS from my "How to Access Weather Data" webpage here.
I've just downloaded the precipitation data for the hydrological year to date. The "hydrological year" begins Oct. 1 and runs to Sept. 30; it includes the winter rainy season that a perennial crop would expect to see. Here is the precipitation data by month to date, as compared to the previous 4 years:
Our National Weather Service and NOAA (the National Oceanic and Atmospheric Administration) publishes a climate prediction page on their website. Their 3 month prediction for precipitation shows "a" or "above average" for Southern California, continuing, though not as strongly, for the foothills:
This is great news! However, if we look closer at the forecast, NOAA's three month outlook for temperatures also shows an "A" or above normal forecast: