may-jun-2020

TIME TO CONSIDER Irrigation, nutrition and pest management are top priorities as hull split approaches. As it is every summer, the overall goal is really two goals: maintain the current crop while not shorting the 2021 crop. Cost savings without harming the crop are key considerations. Usually, cost savings come with more time and management inputs and must be approached cautiously when tried the first time. Possible opportunities for savings include reduced water use at hull split and mite management. There may be others that individual operations can identify. Irrigation David Doll said it several years ago in this space and it is worth repeating (or paraphrasing), “Get your irrigation right and you are more than halfway to successful almond growing.” Maintain adequate orchard irrigation through May using plant, soil or crop water use estimates measurements to keep orchards from water stress levels that reduce yield and increase stick tights. Crop water use estimates (ET), soil moisture sensors and/or plant moisture status are all effective tools. The gold standard for irrigation monitoring is plant moisture status measured as stem water potential (SWP) using a pressure chamber. Keeping the orchard at SWP above -14 bars is the goal heading into hull split. Target SWP is -6 to -10 bars for low tree stress and -10 to -14 bars for mild tree stress. An orchard managed for low stress, where all or part of the orchard occasionally drops into mild stress, should not see reduced yield. There is no consensus for which irrigation strategy (low stress versus mild stress) is the best long-term plan for an orchard. Mild water stress during early hull split can save water, reduce hull rot and may produce more uniform hull split. The goal is to reach a SWP of -14 to -18 bars by the very start of hull split and to hold the orchard at that mild stress level until almost complete hull split (90 percent of nuts have split but are not dried). Start imposing reduced irrigation slowly. Once kernel fill is complete, gradually back off on irrigation set length by 10 to 20 percent and check SWP to track tree response. Then return the orchard to full ET heading into harvest and irrigation cut off. In orchards with low water stress through the spring and heavy textured soil with large water holding capacity, it may take several weeks to get the orchard SWP to the target levels. UC research suggests this practice will save 10 to 15 percent of your annual water use, plus reducing hull rot and may change hull split pattern. If the trees are already short on water before June, this program is not advised. Also, be very careful with this practice in young orchards. SWP in the range of -14 to -18 bars will stop shoot growth and reduce yield potential in future years. For growers with no experience with the pressure chamber, all these numbers may seem a little overwhelming. But once you try it and play around with different irrigation set timings and how those changes influence SWP, you may be surprised how quickly you come to rely on the numbers. A good place to test drive using the pressure chamber is an orchard with heavier soil and/or microsprinkler irrigation, as SWP will change more slowly with a bigger “water bank.” IN YOUR ORCHARD 3 8 A L M O N D F A C T S