Abstract
Timing of azoxystrobin application for control of potato black dot was evaluated at two to four discrete times during early growth stages of potato from planting to just before row closure in trials from 2003 through 2006. Application timings consisted of a single application of azoxystrobin made either at planting, 34, 43, or 60–62 days after planting. Black dot severity was evaluated on above- and below-ground stems using three assessment methods. Incidence of infected progeny tubers and yield were also determined. Application at 60–62 days after planting was the most efficacious timing when black dot was evaluated as frequency of detecting Colletotrichum coccodes from 0.5 cm stem sections taken from near the plant crown in 2 of 3 years, as distance of sclerotium expansion on stems in 1 of 2 years, and as sclerotium density on stems 2 of 3 years. Black dot severity was not reduced as evaluated by any of the assessment methods when application of azoxystrobin was made at planting. Below-ground stems had more disease than the above-ground stems as measured by frequency of detection of C. coccodes near the crown 2 of 4 years, distance of sclerotium expansion on stems 2 of 2 years and sclerotium density on stems 3 of 3 years. Disease severity between above- and below-ground stem segments were highly correlated for all disease assessment methods and years except for frequency of detection of C. coccodes from crown tissue in 2005. There were no statistical interactions for any of the disease severity assessment methods between above- and below-ground stem segments with azoxystrobin timing. The sclerotia assessment on above-ground stem segments at end of season was an efficient measure of black dot. Incidence of infected progeny tubers was significantly reduced compared to the non-treated control when application was made at 62 days after planting in 1 of 3 years and at 34 and 43 days after planting in 2 of 4 years. There was not a significant difference in yield between any of the application times and the non-treated control in any year.
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Acknowledgements
We thank the Washington State Potato Commission for financial support of this project. PPNS no. 0473, Department of Plant Pathology, College of Agriculture, Human, and Natural Resource Sciences, Agricultural Research Center Project no. WNP00678, Washington State University, Pullman, WA 99164-6430.
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Cummings, T.F., Johnson, D.A. Effectiveness of Early-season, Single Applications of Azoxystrobin for the Control of Potato Black Dot as Evaluated by Three Assessment Methods. Am. J. Pot Res 85, 422–431 (2008). https://doi.org/10.1007/s12230-008-9040-4
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DOI: https://doi.org/10.1007/s12230-008-9040-4