may-jun-2020

Summer is Prime Time for ASD Timing is another key consideration with ASD. Most old orchards are pulled out immediately following the latest harvest. By the time growers implement Whole Orchard Recycling — or at least have their woody material trucked away to a co-generation plant — it’s often late September or early October. For growers who want to get new trees in the ground before the next spring that doesn’t typically leave enough time for ASD to be completed while temperatures still are warm. “I would caution against a grower trying to perform ASD within such a tight time frame,” Browne said. Under an ideal scenario, ASD would take place during the summer, after the soil has been well prepared. This would also give growers time to finalize logistics, such as irrigation and water sources and tarping. “Our general impression based on experiments over the years is that we’ve achieved the best results when we’ve treated in July, August or early September,” he said. “The main reason for that is soil temperature, which helps the microbial community in the soil rapidly use the substrate and generate anaerobic conditions and molecules. “That means, under most circumstances, taking a year off and not immediately replanting will provide the best results. This can also reduce replant disease, help with land preparation and irrigation installation and, on some larger operations, could provide significant water savings.” Next Steps in Research So far, ASD in almonds has occurred only under trials in grower orchards in part because Browne and his colleagues are still trying to answer all their questions and, in part, because of cost. ASD can run as high as $2,000 per treated acre — about twice as much as fumigation. Thus, the team is continuing to see how to refine or minimize inputs to help lower the cost, such as using almond hulls & shells as the substrate. Another focus of Browne’s research is to better understand what groups of microorganisms — fungi, bacteria — contribute to PRD, which is essential for his team to understand when testing soils to determine if they have PRD. In addition to ASD's potential to minimize replant disease, current research is also looking at its potential to be effective in reducing plant parasitic nematodes such as ring, lesion, and rootknot nematodes. Andreas Westphal, a specialist in nematology at the UC Kearney Agricultural Research & Extension Center in Parlier, is heading up this area of research in conjunction with Browne’s team. Who May Benefit Now? In the short term, Browne and Ludwig both envision a scenario where ASD could work for growers who need to treat their soil near homes, schools or other spaces where fumigation is not an option. “I think a grower should start small, in an orchard where it might be more complicated to do fumigation,” Browne said. “They may be leaving that ground untreated, but if so, that’s an area where they may want to consider ASD.” Early yields in effectively ASD-treated soil are on par with those seen after fumigation and, in Browne’s research, about twice has high as the untreated soil in control groups. That leads him to believe there may be a future for ASD. He IN YOUR ORCHARD 3 6 A L M O N D F A C T S