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Sunburn On a recent summer morning Jack Vickrey of Vickrey Orchards plucks a walnut hull from a tree on the westernmost edge of a family orchard to showcase the early signs of sunburn. “Weʼre a little bit behind this year,” he says of spraying his Tulare orchard with the kaolin clay. The variety is one of the most susceptible of its kind to sunburn, which occurs wherever direct sun hits the trees. “By the time itʼs high noon these things are cooking,” says Vickrey of the trees in high heat. Sunburn on hull of a walnut will darken the nut inside. “It will literally shrivel up the nut,” he says. After every crop a farmer sees 100 or so nuts sampled, and this is used to determine its price. The appearance of the nuts are graded by a third party and measured to determine the ratio of edible meat to total weight, called the “crack out.” “Thereʼs very little desire for a dark nut,” says the farmer of the grading process. “The darker the nut the less you get paid.” When it comes to fighting sunburn, Surround is the preference of farmers like Vickrey, who typically use it from a ground-based sprayer such as the one that doubles duty for insecticide at Vickrey Orchards. The farmer uses a mix that requires 100 gallons of water to the acre, adding 25 lb. bags of the kaolin clay mixture and 300 gallons of water into a special mixing device designed to keep the mixture moving and unsettled. The mixture is finished off in the sprayer tank, which had its three nozzles per side tuned for the slow-but-steady task of cruising through the orchard and applying the mixture evenly. “In the beginning itʼs a little hard. After you learn, piece of cake,” says Jose Michel, one of two foremen at Vickrey Orchards. In contrast, Diffusion O is typically delivered along with 30 gallons of water to the acre, aerially. Diffusion is based on calcium carbonate, as opposed to the kaolin clay of Surround. Diffusion’s calcium carbonate does not have the pest control side-effect that Surround has and makes it a favorite of farmers like Vickrey. But while it doesn’t have a secondary effect on pests, “it can drop the leaf temperature by 8 to 10 degrees because it’s more of a reflective material,” says Giannecchini, the pest and crop expert. And whereas kaolin clay-based Surround may be so effective that it can actually slow down photosynthesis, the crop expert says the calcium carbonate in Diffusion O allows photosynthesis to occur at it a more regular rate. Orchard gazers may note the difference between the two in that Diffusion O will provide a white film but appears more as a clear coating, which still stands in crisp contrast to untreated trees but isn’t as noticeable. Pests The pest-deterring effects of the kaolin clay sunblock draw to it usage from both organic and non-organic farmers alike, who count on it to protect against the codling moth and husk fly, two major threats to local walnut crops. Up until the walnut husk begins to crack around September, walnut farmers are careful to monitor for the pest, with pest control advisers like Giannecchini and his team scouting for moths once a week. They set up traps and collect data. The sunblock helps in the meantime: the “edginess” of the kaolin clay, for example, helps protect the husk from the stinging of the husk fly, which leaves larva to feed and rot the husk, turning it black. A local organic walnut farmer may choose to use more of the mixture than one that uses pesticide, thanks to the pest-deterring effects. Giannecchini notes that some farmers blow it, “all over the scaffolds of the tree” with the idea that, “it basically houses scale” in the mixture. He explains walnut scale are “little crawlers that will basically feed on the leaves,” and, “can open up routes for a fungal pathogen,” adding, “you may not really see them, but they’re there.” There are other pests, too, beyond the scope of sunblock. “Mites will flare up in a heatwave,” warns Vickrey. Farming The choice of tool — and sunblock — is up to the farmer. “Some guys have preferences over others,” says Giannecchini, whose company sells the crop consultant, whose company distributes the sunburn protectants. “Some growers that prefer Surround over Diffusion, and some that prefer Diffusion over Surround.” But it’s not just picking the material. It’s also picking how much and when to spray, or about when not to spray, be it for outdoor temperature or the watering cycle. The strategy can be tricky, says Vickrey. “Itʼs really a timing thing,” he notes. And even when applied right, sunburn can still be a factor when it comes time for the crack out. A learning experience seems all part of being a Yolo County walnut farmer, however, with the Tulare variety being a prime example of the learning curve seen by experimental farmers as the region expanded to becoming a top-5 product for the region in terms of export value. The Yolo walnut crop now spans 13,800 harvested acres and yieldded $1.39 per acre in 2016 according to the latest Yolo County Crop Report. According to the county crop report, walnuts generated $34.2 million in 2016, $36.7 million in 2015 and $70 million in 2014. The walnut crop value is dictated in part by global markets and competition from outside countries like Chile. With the market seemingly moving toward high-density varietals like Chandler walnuts, the local spotlight may have moved on from the Tulare variety even if the sunburn has not. “I donʼt know many people that have Tulares that are planting more Tulares, Iʼll put it that way,” says Vickrey of the trees. “Nobody really knew at the time. They were the latest and greatest 10-15 years ago.” “Thatʼs one of the thought things about orchard farming,” says the farmer. “The problems are not immediately known.” Just like a good sunburn, or a bug bite, so too with growing trees.]]>

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