|Kryptonite for boxwood blight: Management with fungicides and sanitizers.|
J. A. LAMONDIA (1), S. M. Douglas (2), K. L. Ivors (3), N. Shishkoff (4). (1) The Connecticut Agricultural Experiment Station, Windsor, CT, U.S.A.; (2) The Connecticut Agricultural Experiment Station, New Haven, CT, U.S.A.; (3) North Carolina State University, Raleigh, NC, U.S.A.; (4) USDA ARS FDWSRU, Frederick, MD, U.S.A.
Trials were conducted to evaluate <i>in vitro</i> and <i>in vivo</i> fungicide activity and sanitizer efficacy against the boxwood blight pathogen <i>Calonectria pseudonaviculata</i>. Twenty fungicides from 13 FRAC groups were evaluated for effects on conidial germination and mycelial growth using <i>in vitro</i> assays. Boxwood plants were inoculated 24 to 48 hr after application of fungicides with <i>in vitro</i> activity. Disease progressed over six weeks from leaf and stem lesions to defoliation. Products containing propiconazole, myclobutanil, thiophanate-methyl, fludioxonil, pyraclostrobin, kresoxim-methyl, and chlorothalonil had significant efficacy with 90% to nearly 100% control when applied preventatively. Systemic plus protectant fungicides in a single application resulted in superior disease control compared to systemic fungicides alone. Sanitizers were assessed for their effects on mycelial growth, conidial germination, and microsclerotia using <i>in vitro</i> assays with serial dilutions and contact times. Depending on fungal structure and experimental conditions, sanitizers including O-benzyl-p-chlorophenol, 70% ethanol, sodium hypochlorite, hydrogen dioxide, hydrogen peroxide, peroxyacetic acid and octanic acid were effective with contact times as short as five minutes. These results will help refine current best management practices. Management of boxwood blight will rely on integrated best management practices, sanitation, cultural controls, cultivar resistance and fungicide application.