Walnut panel: tree stress key to irrigation decisions ByDennis Pollock
can trigger kernel darkening. Shackel said it is important todetect tree stress by measuring stemwater potential and to accurately determine irrigation needs, instead of letting worry drive wa- tering decisions. “Do growers irrigate when trees are stressed,” Shackel asked, “or when they are stressed?” His insights were among many point- ers sharedby farmadvisors during theUC
Cooperative Extension Virtual Statewide Walnut Series 2022. Participants also discussed how sani- tation of tools can prevent the spread of crown gall, and how overly wet soil can spreadwalnutblight.Anagricultural econ- omist weighed in on walnut pricing and exportmarkets. Bruce Lampinen, a UC Davis farm ad- visor, said light availability can influence nut sizeandcoloration.He recommended
training trees to a central leader configu- ration and avoiding mechanical hedging when possible. LikeShackel, Lampinenurgeddelaying irrigation in spring, harvesting in a timely manner, andsweepingandpickingupnuts as quickly as possible after shaking. Mae Culumber, a UC nut-crops advi- sor for Fresno County, said nutrients are best applied when the tree can use them in amounts that will not leach past the root zone. She said soil sampling “to establish nitrogen credits” should be conducted regularly. “Be aware of different soil types within fields and sample separately,” Culumber said. Water should be sampled to determine the contribution of nitrogen, she said, and it should occur at various times of the year.Wells should run 30minutes before
When deciding whether to irrigate walnuts, it’s important to consider what’s more stressed—the trees or the grower. Ken Shackel, a plant sciences professor at theUniversityofCalifornia,Davis, said it is important to let thewalnut tree “tell you when it’s time to start irrigating.” Shackel says it can be a mistake to begin irrigating too early. That’s be- cause maturity and excess irrigation
Weeds are planning their attack. Are you?
See WALNUTS, Page 27
Webinar series to focus on issues of food supply chain UniversityofCalifornia specialists inag- ricultureeconomics and foodsystemswill join farmers and farmadvisors in a three- day webinar on current issues impacting the food-supply chain. The April 26-28 series, “Local Food: Shor tening the Supply Chain and ReducingFoodWaste,” is sponsoredby the UCThelmaHansenFund andopen to the public. Online attendance is free. UC Berkeley agricultural economics professor and Wolf Prize laureate David Zilberman will discuss the food-supply chain and impacts of socioeconomic and environmental factors. Diana Winter, deputy director of the UCLA Resnick Center for Food Law and Policy, will outline current food sustain- ability initiatives at federal, state and lo- cal levels. Annemiek Schilder, director of UC Cooperative Extension, posed a question in a statement announcing thewebinar. “Do you ever wonder how far your food t ravel s before i t gets to your plate?” said Schilder, who also directs the UC Hansen Agricultural Research & Extension Center in Ventura County. “Local food hasmany benefits: a smaller carbon footprint, supports local farmers and businesses, and is likely to be fresh- er, tastier and more nutritious.” Discussions will cover food systems in Californiaandhowtheycontributetocom- munity health, with presentations froma farmeronlocal foodproductionanddistri- butionandareportonaschool district that preparesmeals with local ingredients and turns cafeterias into classrooms. To register and find more informa- tion, including speaker biographies, visit ucanr.edu/HansenFoodSystems.
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10 Ag Alert April 13, 2022
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