LAUSR

Abstract Calonectria pseudonaviculata (Lombard, Crous, Wingfield & Wingfield) causes a severe blight disease on boxwood known as “boxwood blight”. Three isolates: 11-9-4a and CTWH1 - wild types from Connecticut landscapes, and FC1 - an isolate of 11-9-4a that was selected for ability to grow on up to 250 μg a.i./ml pyraclostrobin fungicide, were evaluated for sensitivity to nine fungicides belonging to the demethylation inhibitor ([DMI] propiconazole, tebuconazole, triflumizole, myclobutanil, tetraconazole) and strobilurin (pyraclostrobin, azoxystrobin, trifloxystrobin, kresoxim-methyl) groups. The effects of fungicides on mycelial growth and conidial germination were analyzed using in vitro assays. All DMI fungicides strongly inhibited radial growth, but did not prevent conidial germination. Of the strobilurins, only pyraclostrobin inhibited mycelial growth and conidial germination of the 11-9-4a and CTWH1 isolates within label use rates. Pyraclostrobin, kresoxim-methyl, and trifloxystrobin inhibited myc...