Evaluate Actigard applied through drip irrigation for suppression of Xanthomonas contamination in carrot seed
B. WU (1), R. Simmons (2), K. B. Johnson (3), L. J. du Toit (4)
(1) Oregon State University, Central Oregon Agricultural Research Center, Madras, OR, U.S.A.; (2) Central Oregon Agricultural Research Center, Madras, OR, U.S.A.; (3) Oregon State University, Corvallis, OR, U.S.A.; (4) Washington State University, Mount Vernon, WA, U.S.A.
Phytopathology 101:S194

Bacterial blight caused by Xanthomonas hortorum pv. carotae (Xhc), is the most important disease on carrot seed crops in the Pacific Northwest because contaminated seed is the primary inoculum for this disease in commercial carrot production. Currently, there is no effective way to control seed contamination, and seed lots commonly require hot water-treatment, which is expensive and reduces seed vigor. The objective of this study was to evaluate Actigard, a systemic resistance inducer, applied through drip tapes for suppression of Xhc in carrot seed crops. In two greenhouse experiments, 6-week-old carrot seedlings in 4-inch pots were drenched with 0, 5, 10, and 15 mg Actigard, and inoculated with Xhc suspension 1, 3, and 6 wk after. The results on dose and timing effects of Actigard drench were inconsistent. Suppression of Xhc was observed positively related to the Actigard dose on plants inoculated 6 wk post-drench in the first experiment and 3 wk post-drench in the second experiment. In a field trial, Actigard applied through drip tapes two to three times at 2 to 8 oz/A was compared with the commercial standard, two foliar ManKocide sprays. Similar to ManKocide, Actigard applied through drip irrigation reduced Xhc contamination on carrot seed although it did not control Xhc population on leaves and umbels. The results revealed that Actigard through drip is promising for suppression of Xhc on carrot seed, and more studies are needed to optimize method, timing and dose of Actigard application.