A SPECIAL GROWERS’ REPORT OF AG ALERT ® CALIFORNIA Trees & Vines ®
Floodwaters inundated almond orchards in San Joaquin County in January, overwhelming farmers’ ability to pump out excess water. Many trees were later infected by a water mold, Phytophthora.
Flooded almond orchards impacted by deadly mold By Vicky Boyd
“Unfortunately at the time, there wasn’t any place to pump the water because every- thing was full for an extended period of time,” Brumley said. As a result, he lost a number of almond trees fairly quickly once leaves began to emerge. “They leafed out, and we could see they weren’t going to make it,” he said. “Partly it was due to Phytophthora, and also some trees were in saturated soil, and the roots couldn’t get oxygen.” In addition to near-record rains this winter, Cook pointed to a number of other possible reasons for increased Phytophthora infections, including overall larger almond acreage and new orchards being planted on marginal soils that may not have the best drainage. “This is at least four to five times worse than it was back in 2017,” he said. “Now we have a lot more plantings of trees. And the other things we have are lots of plantings of trees on poor soil. That’s what’s driving it. We have trees on rice ground. We have trees in creek beds. We have trees everywhere.” Knowing clay soils can be tied to poor drainage, some growers planted almond trees on berms to keep tree crowns above water and keep roots aerated. Even that didn’t work in many cases this year. See MOLD, Page 8
Winter rains may have brought welcome relief from the prolonged drought, but they also flooded many almond orchards, causing some tree roots to drown or become infected with a frequently lethal water mold. Jim Cook, a pest control advisor who heads research for Colusa County Farm Supply in Williams, said he is seeing more almond trees damaged by the mold Phytophthora than he can remember. While checking almond orchards where growers had reported concerns in early spring, Cook said he found 30 out of 30 were infected with the disease. His field identifications were subsequently confirmed by laboratory testing. Brent Holtz, University of California Cooperative Extension pomology farm advisor for San Joaquin County, said he also has seen several orchards in the Sacramento-San Joaquin Delta devastated by the disease. “In some of the almond orchards in the delta where they couldn’t pump the water off fast enough, I’ve seen quite a bit of Phytophthora out there,” Holtz said. “Out on some of the islands where they were pumping and lost power, it’s catastrophic.” Phil Brumley, who grows almonds and walnuts near Escalon, said he had some flood- ing issues in late February and early March in his orchards, mostly along creeks and in low places.
July 19, 2023 Ag Alert 7
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