Nitrogen Fertility and Mowing Height Affect Fungicide Control of Anthracnose.

Increased nitrogen fertility and mowing height decrease the severity of anthracnose (caused by Colletotrichum cereale Manns) of annual bluegrass (ABG; Poa annua L.) and thus may reduce fungicide inputs. A field trial was initiated in 2012 to evaluate the effects of mowing height, N fertility, and fungicide programming on anthracnose of ABG turf grown on a Nixon sandy loam in North Brunswick, NJ. Treatments were arranged in a 2 x 2 x 6 factorial using a split-split-plot design with four replications. Main factors were mowing height (2.3- or 3.2-mm), N fertility (100 or 200 kg ha^-1 yr^-1), and fungicide program (no fungicide; calendar-based applications of 2+2.4, 4+4.9, 6+7.3, or 8+9.8 kg a.i. ha^-1 of chlorothalonil+fosetyl-Al, respectively; or threshold-based applications at 8+9.8 kg a.i. ha^-1 of chlorothalonil+fosetyl-Al). As expected, greater N fertility, increased mowing height, and fungicides reduced the area under the disease progress curve (AUDPC). Nitrogen fertility, fungicide rate (calendar-based treatments), and the interaction between these factors accounted for 90% of the AUDPC response during 2012 and 2013. The lowest fungicide rate provided acceptable disease control under greater N during 2012; whereas, disease control was often unacceptable at the greatest fungicide rate under lower N. A three-way interaction (2013) indicated that maximum AUDPC reduction occurred at a lower fungicide rate when greater N was combined with higher mowing. Nitrogen fertility and mowing height also affected threshold-based fungicide control of anthracnose. Two threshold-based applications were required for acceptable disease control under greater N and higher mowing, compared to five applications under greater N and lower mowing, or nine applications under lower N, regardless of mowing height during 2012. Results for the third year of this study will be reported.