36th International Carrot Conference Abstract

Investigating performance of reduced risk fungicides for foliar disease control in carrot

Stephen A. Jordant¹, Kenneth Frost², Amanda J. Gevens³

¹Associate Researcher, Department of Plant Pathology, 693 Russell Laboratories, University of Wisconsin, Madison, WI 53706 sjordan3@wisc.edu (608) 219-6811; ²Research Associate, Department of Plant Pathology, 574 Russell Laboratories, University of Wisconsin, Madison, WI 53706 kfrost@wisc.edu (608) 262 – 9914, ³Assistant Professor and Vegetable Pathology Extension Specialist, Department of Plan Pathology, 689 Russell Laboratories, University of Wisconsin, Madison, WI 53706 gevens@wisc.edu (608) 575-3029.

Alternaria leaf blight, caused by the fungus Alternaria dauci, and Cercospora leaf spot, caused by the fungus Cercospora carotae, infect carrot foliage and are the most prevalent foliar diseases of the crop worldwide. These foliar pathogens reduce yield by limiting photosynthetic capacity and by weakening the petioles needed for mechanical harvest. Environmental conditions influence the occurrence and progression of these foliar diseases of carrot. Several new reduced risk fungicides for carrot foliar disease control are now available, however, efficacy of these new fungicides compared to conventional standard fungicides is not well understood. In our trials in 2011 and 2012 in Central Wisconsin, we evaluated the performance and timing of fungicides for foliar disease control in carrot. In both years, fungicide applications were initiated at the first sign of foliar disease, with a subsequent application every two weeks for a total of 5 applications. The severity of foliar disease was measured using the Horsfall-Barrett scale with a final conversion to Area Under the Disease Progress Curve (AUDPC). At the end of the growing season, plots were harvested to determine yield.

In 2011, six fungicide treatments were tested against an untreated control. Bravo Weather Stik, Quadris Top, Inspire XT, Omega 4C (two rates) and A16976 (an experimental chemistry from Syngenta) all delivered significant control of foliar diseases when compared to the untreated control. Among the six fungicides, Omega 4C (both rates) had significantly less control of foliar diseases. Yield, while not significantly different, was higher numerically in the fungicide treated plots.

In 2012, the trial included the same treatments as 2011 plus several treatments of Bravo Weather Stik with a reduced number of applications with alternative timings. Moderate disease pressure was observed in the untreated control at the final rating, which had the highest AUDPC rating. The AUPDC of the untreated control was significantly greater than all but 2 of the two-application chlorothalonil treatments, (Bravo spray 1,3 and Bravo 3,5). Four treatments resulted in significantly greater yields than the untreated control, and included Bravo Weather Stik for 5 applications, Quadris for applications 1, 2, 4, 5 + Bravo Weather Stik at application 3, Quadris Top for applications 1, 2, 4, 5 + Bravo Weather Stik at application 3, and Omega 4C for applications 1, 2, 4, 5 + Bravo Weather Stik at application 3. All of the statistically highest yielding programs included a fungicide treatment in each of the 5 bi-weekly applications.

Last updated Thursday, 25-Jul-2013 11:54:31 CDT