Anthracnose Development on Annual Bluegrass in Response to Nitrogen Carriers and Fungicide Application1

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Abstract
Anthracnose caused by Colletotrichum graminicola (Ces.) Wils., is a serious disease of annual bluegrass (Poa annua L.) turf. In the northern and pacific‐northwestern United States, annual bluegrass is the predominant golf course turfgrass and in some instances the main turfgrass species of home lawns. In turf, cultural practices are effective ways of controlling many turfgrass diseases. However, no reports are available on cultural practices that may reduce or control anthracnose development on annual bluegrass. The purpose of this study was to look at one cultural practice, N fertilization, along with fungicide treatments for controlling anthracnose. A field study was initiated in November of 1979. Three N carriers (isobutylidene diurea, sulfur‐coated urea, and urea), applied at two rates (1.46 kg N/are/year and 2.92 kg N/are/year) and two timings spring (April initiation) and summer (June initiation), with or without fungicide treatments were evaluated for anthracnose control. Triademefon [1‐(4‐Chlorophenoxy)‐3,3‐dimethyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone] fungicide treatments provided the most effective management of anthracnose. Fungicide treated plots averaged 1.9 and 1.7% infected area for 1980 and 1981 whereas non‐fungicide treated plots were 29.6 and 30.6% infected, respectively. Type of N carrier, whether isobutylidene diurea (IBDU), sulfur‐coated urea (SCU) or urea, had no effect on anthracnose development. Moderate N levels (1.46 kg/are/year) were associated with less disease incidence than the higher level of N (2.92 kg/are/year). Nitrogen applications during the months of June, July, August, September, and November resulted in less disease than N applied in April, May, June, August, and September. Growth chamber inoculation studies showed the number of acervuli formed decreased with increasing N at 22 C. At 32 C, the number of acervuli decreased with increasing N to 0.90 kg/ are but increased at the 1.80 kg/are N rate. In conclusion, N fertilization program of applying moderate levels of N (1.46 kg/are/year) with applications beginning in June followed with applications in July, August, September, and November at 0.24, 0.24, 0.24, 0.24, and 0.48 kg N/are, respectively, resulted in less anthracnose damage than the higher level of N (2.92 kg/are/year) or the alternate application schedule (April, May, June, August, September). If the N program was combined with fungicide applications, anthracnose was effectively controlled.