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
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!
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
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
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...
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.
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.
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
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.
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
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!
Happy New Year 2018 Fodder Folks! 2017 ended for me with a trip to South America, in order to participate
In Chile, growers are looking to sustainable farming methods.
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.