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Foothill Fodder

  • Drilling for Microbial Gold: Eskalen Lab Researchers Seek Biocontrol Agents for Canker Disease

    Aug 15, 2019

    Marcelo Bustamante, PhD student in Akif Eskalen's lab, is on a mission.  A sort of microbial safari.  Only the fungi and bacteria Marcelo is collecting aren't easy to catch-they live inside the grape vine, potentially protecting it from deadly canker disease organisms.  To capture these microbes, Marcelo and his lab mates use a sterile drill bit to drill a small hole in grape vine trunks and cordons, and then carefully collect the sawdust and drill shavings to culture back in the lab for bacteria and fungi.  They sample both diseased and healthy vines.  The hope is that some of these captured microbes will be antagonistic to one or more of the suite of fungal pathogens that comprise a serious disease complex referred to as "grape vine trunk disease" or simply, "canker."

    Biological control is defined as any activity of one species that reduces the adverse effects of another species.  Living organisms are the agents of biological control, and although we may think of ladybugs and lacewings when we hear the term, bacteria and fungi can be biological control agents too! Microbes can act as antagonists to other microbes, they can out-compete them for nutrients or space, or they can secrete products that inhibit their growth.  In fact, many biologically based pesticides harness the products of microbes, (think Bt or Spinosad).

    The target of this biocontrol search is a formidable one.  Grapevine trunk disease is present in nearly every mature vineyard, shortening its life and productivity.  Some have even referred to the trunk disease epidemic as the "next phylloxera," because the disease is so devastating to vineyards. 

    The disease is caused by several fungi, all entering the vine via spores carried by rain on pruning wounds. Esca (called measles for the spotting on the fruit), Eutypa dieback, Botryosphaeria dieback, and Phomopsis, are all considered grapevine "trunk diseases"-infection can run from the pruning wound all the way into the trunk.  The disease weakens spurs and shoots, in some cases  killing them. Yield and grape quality is decreased.  Eventually, diseased vines

    are no longer worth keeping in the vineyard and need to be pulled and replanted.  

    Since pruning wounds can be susceptible to infection for weeks after pruning, the recommended practices to prevent infection are to prune late, to "double" prune, that is, make an initial pass in winter leaving 12-14 inches-this can be done mechanically-and then come back closer to budbreak when rains are less frequent to do the final pruning cuts, and to apply fungicide "protectants" to pruning wounds.  Growers should also remove all infected prunings from the vineyard, minimize stress to new plantings and carefully inspect new planting material to be sure it is free

    Dead spurs, with no shoot growth, are signs of trunk disease
    Dead spurs, with no shoot growth, are signs of trunk disease
    from pathogens.  Although most growers I know do practice late and double pruning, which is also helpful to prevent frost damage, once the disease is in a vineyard, it is difficult to prevent spread.  

    Enter the Eskalen lab! A group of UC Davis students studying plant pathology under scientist Akif Eskalen to help solve agricultural plant disease problems! Akif has recently taken the position of UC Plant Pathology Specialist, replacing the late Doug Gubler, and we are so fortunate to have him! Under Akif's direction, Marcelo will be culturing probably hundreds of microbes collected from vines.  He'll screen them in the lab, and, fingers crossed, he'll find a few that show promising biological control against canker.  Maybe, just maybe, he'll find some foothill microbial gold.  I'll keep you posted...


    Woman and man kneeling by grapevine.
    I got to help-I love this stuff!


    By Lynn Wunderlich
    Author - Farm Advisor
  • Precision Agriculture: 21st Century Sustainability

    Jul 24, 2019

    Hi Fodder Folks! "Precision Agriculture" is a term you've probably heard.  You may think of farm mechanization, remote sensing, computers, and maybe even drones when you hear it, and you'd be correct in all of those associations.  But does the term "sustainability" come to mind in relation to "precision agriculture"? Precision agriculture seeks to identify in-field variability (and in the foothills, there is ALOT of variability in the soils and topography), and then address that variability in the most efficient way, often using new technology, to ensure a uniform crop and the conservative use of resources resulting in a profitable agricultural enterprise.  Resource conservation, Efficiency, Profitability...sounds like components of sustainable agriculture to me! 

    Agriculture today faces a huge challenge in labor shortages. Only recently have foothill growers been looking at investing in mechanical tools to help them get the work done. Last month I held a field day in collaboration with Patrick Tokar, viticulturalist for Rombauer, the same Napa Valley Rombauer that recently acquired the old Renwood winery and tasting room in Amador county.  (I have a friend who only drinks Rombauer chardonnay-a classic buttery chard that's been

    called a California icon-but what a pity she's missing out on so many other delicious foothill whites! Vermentino, Sauvignon blanc, Rousanne, Viognier, Greco...oh my goodness, another story on that later surely!).

    Rombauer's foothill operation, they've been growing Zinfandel in El Dorado county since about 2007, recently acquired a Pellenc "suck and pluck" style of leafer-a machine

    that removes the leaves typically targeting the fruit zone.  Leaf removal allows light and air to penetrate the canopy, critically important for disease control and for flavor and color development in the fruit.  Brad Sporleder and his team from Evolution Equipment Services in Lodi, dealers of Pelenc
    A canopy that has had the leaves mechanically removed from the fruit zone.
    Vine canopy AFTER leafing.
    equipment, were on hand to explain the leafer's operation and Tiger from Meyer's Vineyard management did the driving.  Patrick noted that it wasn't just the cost of labor, but the proximity of getting labor up to the foothills is a huge challenge in getting work done on time.  The leafer, used on the shady side of the vine rows of course, is used from budbreak to pea sized berries so that it doesn't pull in and damage bunches, and can do about an acre an hour at 2.4 mph. The estimated cost with shipping and set up is about $30,000 (yep, farming
    A man talking to a group of people in a vineyard.
    UCANR Ag. Engineering Specialist Ali Pourezza explains the use of remote sensing during my field day at Rombauer vineyards in El Dorado County.
    is an expensive business to be in).

    In addition to leafing, Rombauer has been using remote sensing and aerial imaging to help them make decisions on the farm.  I invited UCDavis Biological and Agricultural Engineering Specialist Ali Pourezza to explain the fundamentals of remote sensing.  Ali is a recent addition to our ANR Specialist group and is a whiz in creating models of virtural orchards and vineyards and using sensing technology to solve agricultural problems (check out his video of our field day on Ali's twitter!).

    Ali explained to the group that light behaves in 4 different ways when it interacts with plants: it is reflected (which is easy to measure), absorbed (which can be calculated based on reflection), scattered or transmitted.  When using remote sensing, a multi-spectral camera is mounted on either a UAV or a plane, and images taken which give information dependent on the spectral resolution (or band width) of the camera. Models are developed to interpret this information, and, (this is super important), calibrated with accurate ground truth data.  The calibration is also critical, and needs to include a "radiometric" calibration-that is, a calibration with the sun's position during the time of imaging (which won't be the same on any given 2 days).

    NDVI (normalized digital vegetation index), is the most common and uses near-infrared to red light wavelengths in a scale to tell if green (healthy) vegetation is present or not.  Ali said that NDVI values below 0.1 indicate no vegetation, 0.2-0.5 indicate sparse vegetation, and 0.6-0.9 indicate healthy vegetation.   Other, more advanced indices use other spectral bands, such as NDRE or "red edge".  Ali has been doing some research on using hyper-spectral (thousands of bands!) imaging to detect N2 (nitrogen) deficiency in vineyards.  Working with Viticulture Specialist Matthew Fidelibus, who ground-truths the sensing data by taking vine petioles for nutritional analysis, Ali is developing a model to predict

    vine N2 status using the NDRE spectrum. 

    Rombauer is using Ceres Imaging to do their sensing and Jenna Rodriguez (one of our own UCDavis grads now working for Ceres) also spoke at my field day. After Ali's technical "nuts and bolts" talk, Jenna explained how her company uses remote sensing and modeling to interpret the images provided to clients such as Rombauer.  For example, a blue line on a thermal imaging map was interpreted to be a leaky irrigation pipe.  Low chlorophyll in one area of the vineyard could possibly be soil related.

    The tools of precision agriculture and remote sensing can save labor and help pinpoint the need for applications such as fertilizer.  Yet, there's no replacement for "keeping one foot in the furrow", as the late J.C. Walker of UW-Madison, my alma matter, used to say.  Until next time...




    Attached Images:

    By Lynn Wunderlich
    Author - Farm Advisor
  • Look to the Soil to Determine Property Potential

    Jul 18, 2019

    Greetings Fodder Family! How have you been? Well, I hope!  I've been busy too and I've got stories to tell!

    Over the years as Farm Advisor here (gosh, 19 years this October) my job has changed in many ways with the times.  Recently, I have answered more and more inquiries from those who own a parcel and are wondering about agricultural development or those who are looking to purchase.  The foothills, it seems to me, are becoming impacted by a growing California population and those who may be priced out of other locations and seek a rural lifestyle.

    But the "what can I grow?" question, as I call it, is more complicated to answer than some anticipate.  The key is to not have any preconceived notions (this isn't the Valley nor is it the North Coast) and to be open to exploring the opportunities, and challenges, the foothill landscape offers.  The foothills are kind of like Nebraska, whose new slogan is "Honestly, it's not for everyone" (true!)

    The first step to evaluating a property's suitability for agricultural development is to understand the natural resources that parcel offers.  The most important: soils, water, microclimate.  Enter an amazing resource...the Natural Resource Conservation Service (NRCS) Web Soil Survey! I recently received word that after 12 (or more) years of work, the Calaveras and Tuolumne county soil series maps have been added to our NRCS database and included in the Web Soil Survey (WSS).  Calaveras and Tuolumne had been the only 2 California counties for which the soils were not mapped previously.  This work, led by our local Tuolumne county NRCS office headed by Theresa Kunch and her team of soil scientists, represents a wonderful resource for anyone interested in land, for any reason.

    Last fall I asked Andrew Brown, NRCS  Soil Scientist and one of the staff in the Sonora office, to help me explain local

    soils while visiting a landowner.  While visiting his office, Andrew gave me a brief tour of their soil library, where samples of soil class types are stored (sort of like looking at a soil scientist's version of a pinned insect collection!) Each box has a sample of that soil series collected at each "horizon" (unique soil that changes with depth). This is like looking at what a soil pit dug with a backhoe would show you if you had dug to the bedrock of that series.  Soil color
    A soil series box open and showing the soils at different horizons.
    The archived Red Apple soil series
    and texture and the size and shape of soil particles give an indication of the soil's fertility.

    Whenever I get the "what can I grow on my property?" question, I encourage the landowner to dig a soil pit to get a good look at their soils, BEFORE they plant.  Soil depth, texture and percent rock (some of the foothill soils have alot of rocks!) all contribute to a soil's water holding capacity.  Soil is, in some ways, a key to water, and water is a limiting factor in agricultural productivity.  Understanding the soil will help greatly with planting decisions, such as spacing, rootstock, and soil amendments.  

    Take a look at the soil survey map available online, then go out and dig your pits.  Using the WSS may not be easy the first time around, although there are excellent instructions (begin by defining your AOL "area of interest") on the web page.  I also really like the UC Davis California Soil Web Resource app, created by our UCANR Toby O'Geen and his lab and is newly updated for use on a mobile phone or tablet.  I just bookmarked it on my phone homepage, for easy access when I'm out in the field. Check it out!




    Attached Images:

    By Lynn Wunderlich
    Author - Farm Advisor
  • 2018 Vintage Report

    Oct 15, 2018

    Everyone, and I mean EVERY one,  is all smiles as the 2018 California foothill winegrape harvest sails in on cool weather after a bit of a tumultuous season.  Winemakers were giddy and growers still energetic (a rarity come October) as I visited several foothill vineyards to learn how the season wrapped up. 

    "Beautiful acidity" in the later red varieties was the common theme as the cooler August and September temperatures

    allowed fruit to hang and develop flavors.  "The main thing to note is that we're using a lot fewer acid additions than in some years past", said Michael Long, winemaker at Amador Cellars.  "Our Zinfandel, Mourvedre and Aglianico is still hanging, with pH around 3.5 and great acidity."  

    The sigh of collective relief after a season that began for some with a wet bloom, an April frost event, and crescendoed in July with a blanket of high smoke and higher temperatures was almost palpable. Nothing, in the farming world, is ever a sure thing until the crop is in and the bills paid.
    "The biggest signature of the season for us was the April 17 frost", said Jonathan Lachs, who, with Susan Marks, farms a vineyard and makes wine at Cedarville in Fair Play.  The result of the rainy bloom in the Grenache had a positive twist, Susan noted.  "There's some interesting cluster morphology out there, with clusters looser and shorter.  The Grenache has a lovely dark color as a side effect". 

    Although some foothill Zinfandel remained unsold, a continuing trend following last year's Zinfandel dive, demand for Cedarville's organic fruit is up.  "Buyers are very interested in our Zin", Jonathan said, "and some winemakers in the area are showing a renewed interest in Cab. as well, which is so great to see".  

    Other than in frosted locations, yields came in at average to slightly above, although crop estimates may have been misleading early on. 

    Challenges of the season included a high powdery mildew index in the cooler, higher elevations (perhaps the price paid for the payoff in slower ripening later), and mites, especially in some Zinfandel blocks and often brought on by heat and drought conditions.  Some growers buck the miticide train and choose to use biological control to combat mite outbreaks.  "We've been releasing 6 spotted thrips for years", Ann Kraemer, Shake Ridge Vineyards and Yorba Wines, told me.  6 spotted thrips is a generalist predator, which means it will prey on any soft bodied insect it can, including leafhopper nymphs.  It has the ability to get under the webbing of spider mites to attack them, making it an excellent mite predator! 

    But how cool was it really? After hearing all of this praise for a "cooler" season, I compared the weather data from 2018 to the previous 4 years using the Plymouth CIMIS station located in the Shenandoah Valley in Amador.  Turns out, July had a warmer minimum temp. (62°F) than the previous 4 July minimum temps. But indeed, average minimum temperatures dropped to 55°F come August and stayed cool in September too ( 2018 data shown in dark solid line in graphs).  Average monthly maximum temperatures were less than last year (which held record highs), but still slightly higher than the previous other 3 years.







    Concern about smoke due to the Ferguson and Mendocino Complex  fires made for an "oppressive" July-when some days air particulate matter counts were deemed unsafe to work and crews were sent home early-all blew away by August as clear skies ushered in the first whites.  

    As we made it through her vineyard blocks, Ann made one more keen observation.  "There were fewer birds this year.  My owl boxes are empty and even when putting out netting I noticed there didn't seem to be as many birds as usual." One (unproven) theory: the high summer smoke affected the bird population, causing them to fly less or leave. 

    Now that the fruit is almost all in, let's hope the rainy season comes, and our owls return, soon.


    By Lynn Wunderlich
    Author - Farm Advisor
  • Zaccaria's International Team Showcase Irrigation Whiz During Foothill Field Day

    Aug 16, 2018

    With mounting pressure on growers to account for their precious water use, irrigation tools are relevant now more than ever.  Daniele Zaccaria, UC Irrigation Specialist, brought his impressive International team of student researchers and scientists to the foothills August 10 to discuss their study findings and grower friendly irrigation tools at a UCCE field day.  About twenty growers made the trip over to meet with us at Safari vineyards in Pilot Hill, where we have been gathering data for 4 years on the effect of aspect and slope on vine water use.

    Tools for scheduling irrigation fall into three categories: we can monitor the weather, the soil or the plant.  Monitoring weather includes the classic estimation of crop evapotranspiration (ET) using reference ET data (ET0), based on the amount of water an area of well-watered grass uses, and multiplying that number by a suitable crop coefficient (Kc) to determine how much water a crop has used during any given time period.  The idea being, if you can estimate what a crop has used, you will know how much water to replace with irrigation. The reference ET0 depends on temperature and other local weather factors and is available online (for free, you only need to create a login) from 

    CIMIS (CA. Irrigation Management Information System).  CIMIS stations measure the grass ET in different locations, there are currently 2 CIMIS stations in El Dorado County (Camino and Diamond Springs) and one in Plymouth. 

    If we were growing corn or apples or almonds or practically anything else it would end there; you would have the ET0 from CIMIS and a crop coefficient given based on research and you would multiply the two and then, voila!, you would have an estimate of how much water your crop has used.  But alas, winegrape production is more complicated.  This is because winegrapes, as most of you know, are not irrigated to "full ET".  We typically impose an irrigation deficit to winegrapes at key times of the year to increase the quality of the crop and intensify flavors in the berry skins.  So, for winegrapes, we multiply the reference ET0 by a crop coefficient and then by yet another factor for "stress".  The stress factor is one that a grower determines (say, 70%).

    The final equation is: ETgrapes-stress=ET0 * Kc-grapes* Kstress

    Furthermore, the crop coefficient is not one number, but a number multiplied by the amount of shading present.  This grape coefficient was developed based on research conducted in the Valley (where it is FLAT) by our very own UC Irrigation Specialist Larry Williams and Jim Ayars, in which they found a good correlation between the percent shading and the crop coefficient.  The formula they published in 2005 is Kc grapes= 0.017 * % shaded area.

    But how do we get shaded area? And does this formula really work on sloped vineyards?  While many growers may eyeball

    percent shading, Kristen Shapiro and Sloane Rice demonstrated the "Paso Panel" developed by my UCCE colleague and gadget whiz by his own right Mark Battany. Kristen and Sloane have been using Mark's Paso Panel to estimate percent shading in this sloped vineyard site, and have so far found that the Williams/Ayars model to predict Kc does not seem to work accurately on hillside vineyards.

    There are several ways we can monitor the plant to determine vine water needs.  One of the most tried and true is to measure stem or leaf water potential using a pressure chamber.  Guilia Marino, a plant physiologist who hails from Sicily, demonstrated using a pressure chamber to measure vine stress.  To use a pressure chamber, a leaf is bagged (when measuring STEM water potential), allowed to equilibrate for at least 10 minutes, then the petiole is cut and the cut bagged leaf is placed in a chamber.  The chamber is sealed, pressure is applied, and a hand lens is used to note the pressure at which water is pressed out of the cut petiole.  Guilia likened using the pressure chamber to taking the blood pressure of the vine.  If the vine is under alot of stress, it will take more pressure (higher negative reading) to force water out of the xylem of the cut petiole.  I've done some work using the pressure chamber and I think it is an excellent tool for growers to use in the foothills, because it avoids the variability we frequently see in soils and focuses on what the plant is actually receiving.

    Soil moisture sensors are, perhaps, the oldest technology we have and if placed properly, can give us good information about soil conditions in their location.  Pedro Lima of Brazil has been using Watermark sensors to measure soil moisture on the two slopes at Safari vineyards at several depths.  The sensors consist of porous media that require good contact with the soil, so proper installation is critical. Data from the sensors is uploaded to a station so that the sensors themselves remain undisturbed.  The sensor data has shown different tension, likely because the soils on the two slopes are different.  One other important note: beware of rodents chewing your sensor wires! Pedro noted that something (hmmm) was nibbling on the sensor wires which disrupted data collection.  I think these are great tools for young vineyards, when the roots haven't yet penetrated to greater depths.

    But ET isn't only about crop transpiration.  Camilo Souto demonstrated his work measuring soil evaporation (the "E" in ET) using buried canisters and weighing them periodically to determine the component of soil evaporation.  Camilo noted that the top 4 inches of soil is where most evaporation occurs and he has estimated that evaporation of moisture from the soil accounts for 20-30% of seasonal ET!

    The Zaccaria Team ended our field day by discussing how critically important it is for growers to begin using a tool, if they are not already, to better understand water use in their own vineyards.  Not only for improving winegrape quality, but as competition for water resources increases, the cost of water will surely continue to rise (consider the cost of running a pump) and with it the increase in regulations that require growers to demonstrate their good stewardship of water.  Our growing future depends on it.  

    By Lynn Wunderlich
    Author - Farm Advisor
  • Phylloxera: a foothill pest whose time has come

    Jun 17, 2018

    Hello Fodder Family! Whoosh, the 2018 season is beginning to move fast now that things have finally warmed up (wasn't that cool spring weather nice, though?).  Last time here I wrote about a relatively LARGE (in physical body terms, that is) pest of grapevines, today I want to tell you about a tiny one...

    On a farm call recently, I was reminded of a pest I've come to know pretty well since my appointment here in the foothills: Grape Phylloxera (Daktulosphaeria vitifoliae).   I'm still surprised when growers are taken aback from the discovery of Phylloxera on their own-rooted vines that are declining ("REALLY? PHYLLOXERA?").  Yes, really.  When I first started here as Farm Advisor for viticulture many folks told me that there was NO Phylloxera in the foothills, even though my predecessor, Donna Hirschfelt, knew that phylloxera was here and had spoken about it.  And although vines in decline can be due to many different pests (canker, gophers, and Armillaria to name a few), often when I come upon own rooted vines (i.e. those who are not grafted onto rootstock and so have Vitis vinifera as the root) I am able to find phylloxera on the roots.

    How can this tiny insect take down these large vines?  Phylloxera is an aphid like insect that feeds on the roots

    of V. vinifera.  Sometimes called "European grape", vinifera is the Vitis species we grow on the top half of the vine and includes all of the cultivars like Cabernet, Zinfandel, Viognier, Rousanne, Chardonnay, Mourvedre, etc. etc. (oh my gosh...so many wines, so little time!) that we like to sip with our dinner! 

    Phylloxera is native to N. America, so no, we did not get phylloxera from France.  Rather, we unwittingly gave it to the Europeans for which they will never forgive us. When feeding, the phylloxera cause swelling of the roots and their feeding damages the root system so that fungi can infect and decay the roots.  This is why phylloxera infested vines are so stunted and stressed, after awhile, they have little functional root system left.  Thank goodness the plant breeders have come to the rescue to breed hybrids of other Vitis species for our rootstocks, such as V. rupestris (St. George) and V. riparia which are resistant (but NOT immune) to phylloxera.  Andy Walker, our very own UC Davis Viticulture breeder, gave an excellent talk on rootstocks and phylloxera a few years ago at my 2013 Foothill Grape Day.  His presentation is posted on my webpage with all the other Foothill Grape Day presentations our speakers have granted me the OK to post. A great resource if you ever want to check back for some fun facts!

    By the way, there are many ways that phylloxera can spread.  Since our rootstock hybrids are not immune, phylloxera can enter a vineyard on the roots of grafted vines.  From there, phylloxera nymphs or crawlers will periodically climb their way up to the soil surface, where they can easily be carried by the wind.  They can also be picked up on the bottoms of boots and equipment, which is why I always carry a spray bottle of clorox in my truck to spray my boot bottoms off after being in a phylloxera field.

    A few years ago, Kent Daane (UC Berkeley Entomology Specialist and biological control whiz) wondered if phylloxera might be spreading around leafroll (this was back before we knew the ID of red blotch).  I collaborated with Kent and his then assistant Christina Wistrom in a study where we looked at foothill sites that had both phylloxera AND grapevine leafroll virus.  Thankfully, we found no evidence that phylloxera spreads leafroll (but mealybugs, including grape and Gill's mealybug, do).

    As own-rooted vines that are many years old are declining, and as the cost of farming these vines continues to increase, we are seeing many older vineyards being replanted in the foothills.  This is sad to me, mainly because of the family history in many of these vineyards that are as much as 130 years old!  Some winemakers would also argue that these vines produce superior wine, although I think this is in part due to the low yields making fruit highly concentrated (and, for most, growers are paid by the ton, not so much by the age of the vineyard).  But phylloxera is a pest that cannot be managed indefinitely, it eventually will win.  Some growers choose to apply a systemic insecticide for phylloxera management, but these do not kill the phylloxera eggs.  So, we are gradually seeing our historic foothill vineyard landscape change as older, historic own-rooted vineyards are replaced.

    Change, though, can sometimes bring unexpected and good things (I often have to remind myself of this).  Rootstocks today provide growers a large choice of attributes that can help dial in quality for a given "site capacity".  Replanting also gives growers and their winemakers an opportunity to try new varieties that may have a better consumer niche and price for the grower.  And, most importantly, the increase in YIELD that comes with phylloxera free vineyards will allow our foothill industry to stay vibrant and alive!


    By Lynn Wunderlich
    Author - Farm Advisor
  • Vole with a V

    May 17, 2018

    Hi there Fodder Folks! Our agricultural pests come in all shapes, sizes and Phyla, and sometimes the most destructive ones are those that have four legs and fur.  Voles (Microtus sp.), otherwise known as meadow mice and not to be confused with the friendly mole (with a M), can do incredibly destructive damage to trees and vines, especially young plantings.  One of my responsibilities as a UC Farm Advisor is to diagnose problems in grower's fields, and I have had an unusually large number of farm calls this year and last to diagnose vole damage-mainly in vineyards and olive orchards.

    Why all of this vole damage now? Voles love tall grass, which protects them from their natural raptor predators.  Our heavy rainfall in 2016-2017 and in the current season produced a large amount of grassy groundcover.  If this tall grass is not controlled in the tree or vine row, it provides the perfect environment for voles-who make very shallow "runs"-to nibble on tree and vine trunks.  This nibbling can be just below the soil-trunk line, and isn't always obvious.  On a farm call to visit a mature olive orchard, the canopy was so

    sparse, the grower wondered if there was a soilborne disease, or problem with irrigation. All of which are possibilities. But with a trained eye, one can come to recognize the maze of burrows just beneath the soil surface leading to the trees.  I typically feel around the base of the tree or vine to see if I can feel the "run" (after doing so recently, the grower exclaimed, "I thought you were going to pull out a SNAKE!"...hmmm....never thought of that as I
    A vole burrow hole at the base of a a tree.
    Vole burrow holes and "runs" just beneath the soil surface. Look for recent activity (fur, pellets, bare runways).
    was so thrilled to follow the burrows!)

    But truly, vole damage is no laughing matter.  Especially for young orchards and vineyards, where voles can kill the trees and vines.  Young vines with severe vole damage can turn red-sometimes being confused with virus

    infection.  Young vines with carton covered trunks should be inspected regularly by pulling up the cartons on sick looking vines to be sure there isn't any vole damage occurring. In a young vineyard I visited last year, nearly one third of the new planting was destroyed by voles.  That's significant financial damage.

    So, what can growers do to manage voles? #1: keep the vegetation down near the trunks of vines and trees.  Cover crops should be mowed and vegetation kept down in between the rows and on the borders.  Beware of adjacent open spaces, meadows, or other lands where voles may be entering.  Look for vole damage and monitor regularly-look for burrow holes and runs.  Vole populations can reach a high peak and then crash, or they can continue to grow and cause problems.  Activity can be noted by the freshness of the runs, bare ground, pellets, and fur.  Exclusion using a tree guard barrier or along the fence line is difficult.  Since voles burrow just below ground, the barrier needs to be buried at least 6 inches to be effective.  Traps can be used effectively in the vole runs, since voles don't deviate much from their habit trails.  Rodenticides in baits (anti-coagulants that require multiple feedings or zinc phosphide) are restricted use-check with your agricultural commissioner before applying. You will need a permit or a licensed applicator to use them.  UCCE Vertebrate Specialist Roger Baldwin (whose cool website you should really check out), is interested in getting an anti-feedant registered for use against vole damage in CA.  This could be a very helpful tool, and I encourage you to fill out Roger's very brief survey here if you have voles and want a new tool to fight them.

    You can find more information on voles by reading Roger's Chapter here

    Until next time...


    By Lynn Wunderlich
    Author - Farm Advisor
  • Spring 2018 Weather Confounds: Lack of Chill for Trees, Frost Damage in Grapes

    Apr 23, 2018

    If you are a Foothill grower of apples or winegrapes you may see a lighter crop load come harvest time this year, but for very different reasons.  Apple bloom appears light, possibly due to a lack of chilling in February; while lows of 31°F in late March and mid April have caused some frost damage in some grape varieties.

    Remember those 70°F days in early February? While you may have been basking in the California winter weather while your relatives back in the Midwest were freezing (sorry sisters!), our apple, pear, peach and nectarine trees weren't so happy.  That is because pome and stone fruits need a certain amount of chilling during the winter to release them from dormancy. 

    Without this chilling, budbreak can appear erratic, weak and protracted, shoots bare, bloom extended and in some cases reduced.  This can make ripening uneven and difficult to manage, and in the worse case,
    Cumulative chilling hours below 45degrees, Camino CIMIS.
    reduce yield.

    Chilling has historically been calculated by summing the hours below 45°F or the hours between 32°-45°F from November 1 through the end of February.  

    When we look at the Camino CIMIS station's cumulative chilling hours below 45°F for 2017-2018, we can see that we reached only 855 chill hours during this time.  Chilling requirements for pome and stone fruits depend on the variety, but most apple varieties that are not "low-chill" will require between 500-1000 chilling hours below 45°F, while most grapes will need less than 200 chill hours. 

    Recently, researchers have developed what they believe is a better model for calculating chilling, one that takes into account warm weather as well as cold and continues to accumulate into the year. The "chill portions" model for the Camino station is currently at just above 100 "portions" (Gold Delicious require about 50 "portions").  You can learn more about Chill calculators at our UC Fruit and Nut Center website here; or review Farm Advisor Katherine Pope's excellent presentation on chilliing that she gave at my Foothill Tree Fruit meeting a few years back here.

    While February was unseasonably warm, late March and April has had some nights where temperatures have reached as low as 30-31°F.  Once plants break bud, all of their tissue is susceptible to frost damage.  Cold injury to grape green

    tissue begins at air temperatures of 31°F for a duration of a half hour (note: the air temperature is standardized by being measured by a sheltered minimum thermometer four feet above the ground, as temperature can vary due to distance to the ground-the closer, the colder-and whether the station is sheltered).  Air temperatures of 26-28°F for a duration of several hours will kill the green growing parts.  Most often though, we see degrees of spring frost damage.  Shoot tips may be killed or damaged, but clusters that have not yet emerged may be OK.  

    Frost damage actually occurs because of dehydration of the plant cells.  The cells are injured when their contents freeze and expand.  Later, the damaged cells can no longer control their liquid contents, so they dehydrate.

    The degree of frost damage depends on a number of factors: how cold the tissue got (depending on your site microclimate, slope, aspect, etc.); whether there is bare ground, which will absorb and hold daytime heat, or a ground cover or cover crop, which can not hold daytime heat and may even harbor ice nucleating bacteria that allow freezing to occur at slightly higher temperatures.  The carbohydrate reserve that a vine has is also an important factor for susceptibility to frost injury.  A low carbohydrate reserve, due to a super vigorous variety or one which stays growing late into the fall, or those that suffer from water stress (which is why it is advised to water post-harvest if you can), can make a vine more susceptible to frost injury.  

    Recently I observed variable frost damage in Viognier, Nebbiolo, Syrah and Gamay grape varieties growing in El Dorado County.  It is still a bit early to determine how much damage (damage to emerging clusters) was done.  Thankfully, basal buds and a "second crop" may come to the rescue!  Erratic, intensive weather patterns, whether they be cold or warm, appear to becoming more common.  Learning how to farm profitably during these uncertain times is but one of the challenges we face for our farming future.















    By Lynn Wunderlich
    Author - Farm Advisor
  • Are Your Vines in Balance? Foothill Grape Day is March 29!

    Mar 21, 2018

    A red winegrape canopy
    Foothill Grape Day 2018 will be held Thursday, March 29 from 7:30 a.m.to 3:00 p.m. at the Amador County Fairgrounds in Pokerville Hall.  This year's theme is "Vine Balance", which I think of as the sweet spot in growing a particular block of grapes.  This occurs when the vegetative canopy and crop load
    can be sustained and provides the desired grape quality.  

    Vine balance is more than an academic concept.  It is the foundation for making management decisions from planting time (rootstock choice, vine spacing, trellising type) to seasonal (irrigation, fertilizer, cover crop) and cultural options (canopy management, crop thinning) to harvest (grape quality and yield).  It requires an in-depth understanding of your vineyard site

    You don't need a digital scale like this one to measure your fruit weight.
    You don't need a digital scale like this one to measure your fruit weight.
    and the variety and rootstock characteristics.  It also considers weather patterns, for example, what amount of rainfall do you have going into this season, and what is your soil's water holding capacity for that rainfall? What was the season like last year? Were the vines overly stressed due to lack of water (which would affect wood and bud renewal)? To help you determine the vine's balance, you may want to collect some data from your own vineyard blocks: pruning weight and cluster weight information can assist you in assessing how balanced your vines are. 

    To lead the Grape Day discussion on Vine Balance, I've invited the best speakers I know of to address this topic: veteran UCCE Viticulture Advisors from around the state.  Mark Battany, UCCE San Luis Obispo, will discuss below ground factors influencing vine balance.  Mark has a background in soil science and is known as a bit of a "techie" in our group; he created the infamous "Paso Panel" to help measure canopy light interception and has done quite a lot of work on groundwater issues in his part of the state.  Larry Bettiga, UCCE Monterey, will share basic pruning and training principles for balanced vines.  Wondering when cane pruning should be implemented? How to know how many buds to leave on a spur pruned vine? Larry
    Vine balance starts with good vineyard design.
    Vine balance starts with good vineyard design.
    has years of experience conducting trials on the Central Coast.  Rhonda Smith, UCCE Sonoma, will discuss canopy management.  This includes leafing and shoot thinning, row direction and how that affects the canopy and fruit development.  Rhonda is a serious viticulturalist, who carefully considers the consequences of management decisions. George Zhuang, UCCE Fresno, is the newest viticulture advisor on our team.  George has recently completed some trials of crop load on young pinot grigio vines in his area and will share the results of what can happen when you crop too much, too soon.  Glenn McGourty, UCCE Mendocino, is a perennial favorite speaker for Grape Day because of his love of wine and interesting wine varieties.  Who better to discuss the inherent variety characteristics affecting vine balance?  Kaan Kurtural, our UCDavis Viticulture Specialist, has quickly established himself as a workhorse leader in conducting studies pertinent to today's vineyard.  He will discuss affects on fruit quality-the end result of vine balance management strategies.

    Also, as a special treat, Yorba Wines and Shake Ridge Ranch vineyard manager Ann Kraemer has agreed to come and share her techniques for estimating yield and adjusting fruit load.  Ann is a knowledgeable and articulate speaker and I'm grateful to have a grower give practical advise.

    All are welcome to attend Foothill Grape Day.  To register, please go to: http://cecentralsierra.ucanr.edu/Agriculture/Viticulture/Foothill_Grape_Day_2018/

    or contact Robin Cleveland, office assistant extraordinaire, at 530-621-5528, to sign up! I hope to see you there!



    By Lynn Wunderlich
    Author - Farm Advisor
  • South American Grape Growers Plan for Sustainable Future

    Jan 4, 2018

    Happy New Year 2018 Fodder Folks! 2017 ended for me with a trip to South America, in order to participate

    The GiESCO logo
    in the 20th International GiESCO (Group of International Experts of vitivinicultural Systems for CoOperation) meeting held in Mendoza, Argentina, and to do some vineyard field touring with my UCCE colleagues in Chile. GiESCO (a funny acronym, I know) provides a wealth of information, and it is especially interesting to realize that winegrowers and extension researchers all over the world are facing many of the same problems- including drought imposed by higher
    A man in front of a slide with Andean climate statistics.
    Richardo Villalba presents Andean climate stats at GiESCO.
    temperatures and lack of snow, in South America, the Andes Mountains are experiencing an average 15% decrease in flow. Sound familiar? As I write this the temperature is 68 degrees in January and there is no snow in the Sierra.  While historically Argentine growers had canal water for furrow irrigation, today new vineyards must drill for groundwater and use drip irrigation.  The need is for more efficient use of the water they have, while carefully monitoring what is available.

    In Chile, growers are looking to sustainable farming methods.

     Anticipating that glyphosate will no longer be used in 5 years, the Vina San Pedro de Tarapacá Wine Group is experimenting with organic wine growing, using an "intercepa" mechanical weed cultivator.  Since trunk diseases are a major problem there (yet another similarity with CA. grape growing), pruning wounds are routinely treated with protectants. 
    A painted pruning wound.
    Pruning wounds are treated with fungicide protectants to prevent the spread of canker disease.
    Netting is used to protect clusters from the intensity of the sun.  And all winery
    Netting for grape clusters.
    Clusters are routinely netted for sun protection.
    waste goes to a "biodigester", a compost making power plant that supplies hot water, electricity, and compost that goes back onto the vines. 

    Perhaps the most progressive thing that VSP wine group is doing to prepare for a sustainable future is communicating openly about their problems and solutions-because planning for a sustainable future doesn't happen in a bubble.  Turns out it really is a small world, after all.


    By Lynn Wunderlich
    Author - Farm Advisor