Florent Trouillas, a University of California, Davis, plant pathologist, inspects a cherry tree in Lodi. Researchers say threats may be rising for diseases in tree crops after heavy storms. Researchers probe orchards for storm-related pathogens
Researchers say the wave of atmo- spheric rivers that swept across the state this past winter has created the right con- ditions for plant pathogens that haven’t been seen for decades in California. Florent Trouillas, a plant pathologist at the University of California, Davis, said he is getting more calls from grow- ers and farm advisors concerned about potential crop damage. “Generally, whenever you have rain events, you’re going to have prob- lems,” said Trouillas, a Cooperative Extension specialist based at the Kearney Agricultural Research and Extension Center in Parlier. “In wet years, we get really busy because most pathogens need and like water.” Trouillas and other researchers are working to diagnose pathogens, diseas- es and other ailments that strike fruit and nut crops such as almonds, cherries, ol- ives and pistachios. They are tracking potentially destruc- tive tree threats that may be enhanced by the 2023 storm surges. On a recent visit to an almond or- chard near Fresno, Trouillas joined Mae Culumber, a nut crops farm advi- sor in Fresno County. A few weeks earli- er, the two had walked the orchard, tak- ing note of the base of some trees that had gumming—a thick, jelly-looking substance indicating a pathogen had taken hold. “A lot of what Florent is doing is try- ing to assess patterns on a landscape,” Culumber explained. “Sometimes things may look like they are one thing, but it could be another problem.” When the two returned weeks later, the amber-colored gumming had moved into the canopy, looking like gumballs stuck to branches, some of which were already dead. “It’s getting out of control from before,” Trouillas said, noting the changes. “This branch was killed. This is widespread.”
Lab testing later confirmed what Trouillas said he believed was the culprit: Phytophthora syringae, a pathogen that can affect almond crops but is rarely seen in California. The infection is generally found in tree wounds caused by pruning. But that was not the case in this inspection: The in- fection began in the canopy at twigs, or small branches. Researchers are working to keep the pathogen from impacting California’s $5 billion annual almond crop. The last time Phytophthora syringae hit California was in the 1990s after a series of El Niño-influenced storms. “It’s rare for California and one that we see mostly following atmospheric rivers,” Trouillas said. “The disease will only happen following these extremely wet winters.” Phytophthora is soil borne, mostly found in tree roots and doesn’t generally spread up into branches. But Trouillas said the intense storms created the right conditions for the pathogen to “swim” up trunks as winds blew spores into the air and rain dropped them back down into the canopy. He said some of the trees in the or- chard he visited will die. However, he added, others can be saved by pruning infected branches and applying a rec- ommended fungicide. Besides inspecting orchards of late, Trouillas works with pest control advi- sors and others in agriculture on ways to manage potential threats and pre- vent crop damage. Trouillas typically conducts one or two site visits a week, usually after a farm ad- visor reaches out about a problem. One of those calls recently took him to a cherry orchard in Lodi. “These guys help me quite a bit,” said Andrew Vignolo, a pest control advisor
See PATHOGENS, Page 10
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