Identification Before Diagnosis
The key in dealing with both disease and weed problems in tree nut crops is correct identification. By CECILIA PARSONS | Associate Editor
M
ohammad Yaghmour, University of California Cooperative Extension orchard systems advisor in Kern and Kings counties, and a speaker at the Kern Ag Day event in Bakersfield, said growers who spot disease symptoms in their orchards should take samples to a laboratory to confirm a diagnosis. “You have to know 100 percent what pathogen is causing the problem,” he emphasized. Different diseases may have similar symptoms and without a confirmed diagnosis, time and effort can be wasted. He advised the samples to include both healthy and diseased tissue, as the fungus is active at the interface. Yaghmour, who is involved in research in fungal disease in orchard crops, said Phytophthora and crown rot are found in the southern San Joaquin Valley and can kill young trees. Water management, resistant rootstocks and scaffold selection in young trees are effective methods for controlling fungal diseases in nut orchards. Careful soil water management is the best route for control of Phytophthora root and crown rot. Cultural practices that avoid wetting near tree root crowns can help minimize disease losses. Berms can help keep those areas dry, Yaghmour said. Resistant rootstocks are another tool. Those with plum background are less severely affected by Phytophthora. Prevention of infection includes selection of scaffolds to avoid pockets where spores carried on harvest dust can
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West Coast Nut
collect. When the pockets are wet due to irrigation or rain events, infection can occur. Knowing the site history and the level of inoculum in the soil is important. Yaghmour said fumigation or solarization can reduce the level of inoculum, but will not eliminate it. Weed management specialist Kurt Hembree also encouraged knowing the weed species when choosing an herbicide program or cultural practices for control. Choosing and mixing modes of action of herbicides should be a part of the control program to mitigate resistance. He advised mixing modes of action and rotating combinations specific for pre or post emergent weeds to prevent resistance. Modes of action and group numbers can be found on the herbicide labels. Other advice for weed control included applications prior to applying compost materials to orchards. Compost can tie up herbicides, which need to make contact with the soil to be effective. Leaf cover can also deter herbicide action. Paying attention to the physical applications is also important to achieve effective coverage. Applicators need to pay attention to where spray is hitting. Volume and speed must also match targeted weeds. Hembree also advised replacing worn nozzles when they are three to four percent off their delivery range. Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com
January 2019
Walnut trees with crown rot. All photos courtesy of Kathy Coatney.