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April 15, 2016 CapitalPress.com 11 Walnut growers fend off fungal disease Botryosphaeria proves a threat following wet winter weather By CECILIA PARSONS For the Capital Press Wetter than normal winters have the potential to unleash a “sleeping giant” of a disease in walnut trees. Themis Michailides, plant pathologist at the University of California-Davis is warn- ing walnut growers that the canker disease Botryosphae- ria, dodged during dry years, could be a factor in tree health this year. The disease was first dis- covered in a Butte County, Calif., pistachio orchard in 1983, following a wet winter. The disease gathered steam in subsequent wet winters and by 1995 had spread from a few trees in Northern Cali- fornia to Southern California walnut production areas. There was a major epidem- ic of botryosphaeria in 1998, as the fungi attacked branch- es and clusters, affecting crop yields and gaining the atten- tion of growers. At that time, Michailides said, there was no known con- ONV16-2/#5 Cecilia Parsons/For the Capital Press Botryosphaeria has infected these shoots on a mature walnut tree in Tulare County, Calif. trol other than sanitation prac- tices. Many growers pulled their infected pistachio trees after that epidemic and plant- ed walnuts, not realizing the fungal disease also targeted that crop. There are 10 species of Botryosphaeria that affect walnut trees, and all walnut cultivars are susceptible to the disease. Michailides’ research, funded by the California Wal- nut Board since 2012, has found the fungi infect the nut, move to the peduncle and then spread to the spurs, killing the next year’s buds. Tulare County farm advi- sor Elizabeth Fichtner said that several species of the pathogen are associated with branch dieback and bud mor- tality and shoot and fruit in- fections in California walnuts. In the past the dieback has been attributed to shade-out, but Fichtner reports that 84 percent of the walnut samples submitted to the Michailides laboratory at Kearney Agri- cultural Research and Exten- sion Center in Parlier have tested positive for Botryos- phaeria or Phomopsis, also a canker disease. Infected wood, prunings and hulls left in the orchard are a source of the Botryos- phaeria spores. Other hosts for the fungi are blackberry. Scale insects increase the po- tential for infection. In a presentation at the an- nual Walnut Day organized by Cooperative Extension farm advisors, Michailides said the fungi spores are both wind- and water-borne with the ma- jority of spores released with- in 30 minutes of even a short rain shower. Higher tempera- tures contribute to the spread of infection. ONV16-4/#5 541-752-0460 31567 HWY 99 W Corvallis, OR of dead branches, blighted shoots and cankers after winter pruning is essential. Burning is recommended for large branches. Pruning mate- rial that is chipped should be disked under. Other manage- ment strategies include avoid- ing irrigation that dampens the tree canopy. Fungicide sprays also work to control the disease. Grow- ers who want to know the ef- ficacy of particular materials can visit the UC-Davis Inte- grated Pest Management web- site to see the chart: ipm.uc- davis.edu/PMG/r605902111. html. Michailides said if only one spray is planned the best time is mid-June to early July. Bag needs? Bag solutions! SMITH PACKAGING YOUR MAIN SUPPLIER FOR: • Polyethylene Bags • Polypropylene Bags • Paper Bags • Bulk Bags • Stretch Films • Hay Sleeves Products We Sell Include: Pacific Grow Fish Fertilizer Sea Crop Concentrated Sea Water Soil Provide Inoculum Cascade Minerals Rock Dust Perfect Blend Fertilizer Bulk Truckload Pricing Available ALL CERTIFIED ORGANIC Walnuts are unique, he noted, in that pruning wounds leave trees open to infection for a longer time, increasing the risk of infection. One of the first steps in management of the disease is to assess disease risk and cultural control. To have an idea of the level of infection in a single orchard, growers can collect 200 buds through- out their orchard from Janu- ary to March and have them checked for Botryosphaeria using a bud monitoring tech- nique called BUDMON. There are also effective management practices to sup- press the amount of the dis- ease in the orchard. Removal • Mesh Produce Bags • Plastic Pallet Covers • Bag Closure Products • General Warehouse Supplies Competitive pricing! Great quality products! Service you expect and trust! • Halsey, Oregon: 541-369-2850 • Eastern Washington, Ed Kropf: 509-936-2652 or ed@smith-packaging.com www.smithpackagingservices.com ONV16-1/#5
