Ag Alert Sept. 22, 2021

Two research efforts seek powdery mildew solutions

Torres demonstrated how a glove can be used to sweep through the vines. Then the glove is swabbed and the cotton swab is submitted to a lab for an analysis ofmil- dew levels. Torres also showed amildewspore trap that canhelpgrowersget the jumponpow- dery mildew. It can detect mildew pres- ence as early as four weeks before the first symptoms appear on a plant. The traps use a solar-powered mech- anism and molecular analysis for iden- tification. The traps can help flag when a treatment is inorderandcanhelppinpoint

mildew “hot spots.” Taneja said researchers are currently performing proof-of-concept field testing for control of powderymildewat Kearney. Researchers said they believe topical RNA interference could provide an ef- fective and durable biopesticide for pow- dery-mildewcontrolwithanovelmodeof action and could reduce environmental and health impacts compared to current chemical fungicides. Taneja said researchers tested 50 to 60

ByDennis Pollock Powderymildewcanpunchabighole in thepocketbooks of grape growers, costing themup to 4% to 7% of their revenue de- pending on grape variety, growing region and the year’s disease pressures. Now the mildew is at the center of two researcheffortsat theKearneyAgricultural Research and ExtensionCenter inParlier. One study has its feet firmly on the ground,where stepsarealreadybeing tak- en with technologies and chemical tools currently inhand. Another research project looks to the future—and use of genome sequenc- ing—to achieve a better understanding of genes that play a role in growth of pow- derymildew. The delivery systemfor that management step is probably four or five years away. Gabriel Torres, University of California viticulture and enology farm advisor in KingsCounty, addressedthetopicofof cur- rent tools at aGrapeDay event at Kearney. He discussed the challenges of keeping resistance touseful chemicals at bay. Jyoti Taneja, a project scientist with UC Berkeley, talkedabout ribonucleicacid, or RNA, interference technology, which has been shown to be effective in controlling several plant pests. It uses a natural cellu- lar process that employs double-stranded RNA against specific gene transcripts. The Wildermuth Lab at UC Berkeley has developed topical RNA interference technology to control powdery mildew in grapevines. Torres saidusing thesamepesticides re- peatedly can result in resistance to them. He saidRally is themost recent exampleof a fungicide that has been rendered less ef- fective throughdevelopment of resistance. He said it is important to use pesti- cides that have different modes of ac- tion. While they can be used twice in a season, he added, labels on some pes- ticides carry warnings that they should not be used in consecutive sprays.

“You need to rotate fungicides,” Torres said. Hesaidvulnerability topowderymildew is cultivar dependent. He said steps can be taken to improve air flow and fungicide penetration by opening canopies. That also reduces hu- midity inside the canopy.

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September 22, 2021 Ag Alert 9