Issue link: https://www.e-digitaleditions.com/i/1084285
reduce compaction and amending the soil to eliminate soil chemical issues, the better the outcome," Doll said. "This may also mean taking a year off to properly prepare the field and plant cover crops, which have been shown to increase soil structure and organic matter levels." Rotating the field to another crop will help reduce the severity of replant problems while providing time to properly redevelop the field. Reducing rates and emissions While methyl bromide alternatives have proven both efficacious and cost-effective, newer regulations — including township caps on Telone-II, buffer zone regulations on chloropicrin, and the California Department of Pesticide Regulation's School Rule — are putting increased pressure on these active ingredients. Doll's research looked at alternative application rates, timing and methods to reduce emissions, as well as non- fumigant alternatives. Working in conjunction with Suduan Gao, a research soil chemist at USDA ARS in Parlier, Doll found that applying fumigants under special tarps is highly effective at keeping fumigant emissions from moving off-site. The cost of the tarps can be offset by a rate reduction of 25 to 40%. Doll compared broadcast applications to 11-foot row-strip applications, which would effectively reduce applied fumigants by 50%. He also compared them to GPS- guided 8-foot-square spot plantings, 1 which would reduce fumigant applied by 70%. "In reviewing the data over the past two years, we found that row-strip applications of a combination of chloropicrin and Telone-II across trials in nematode and PRD soils yielded similarly to broadcast treatment. Spot treatments outperformed control plots but were not as good as the other two treatments," Doll said. These findings effectively allow growers to stretch fumigant active ingredient use to offset township caps or to reduce the size of the buffer zone. Newer alternatives Doll has also researched multiple alternatives to traditional fumigants, including alternative pesticides and post-plant nematicides. "Plots that were fumigated outperform the alternatives, although post-plant nematicides did outperform control," Doll said. "For nematodes, you may be able to get by with post-plant nematicides, but it depends on how high the populations are and whether a resistant rootstock has been selected." The bottom line According to Doll, "Out of all the work with PRD and parasitic nematodes, the biggest bang for your buck is a row-strip application of Telone-II. The trees will not be as big and they won't yield as much as with the broadcast treatment, but the reduced costs give you the best economic return through the seventh leaf." Doll is confident that fumigation still provides the biggest return on investment over its alternatives. "Both fumigants can stand in for each other in some cases, but they are better off used in combination," Doll said. "They are really valued, and we need to keep both as effective tools." "The more time growers spend cleaning and preparing the field, eliminating roots, ripping the soil to reduce compaction and amending the soil to eliminate soil chemical issues, the better the outcome." – David Doll 1 Spot plantings developed with Almond Board funding to Dr. Shrinivasa K. Upadhyaya, professor of biological and agricultural engineering at UC Davis. 17