High N Rate Fertilization Effects On Anthracnose Severity of Annual Bluegrass Turf.

Anthracnose, caused by Colletotrichum cereale Manns, is a destructive disease of annual bluegrass [ABG; Poa annua L. f. reptans (Hausskn) T. Koyama] putting green turf that is exacerbated by inadequate or excessive fertilization.  Previous work has indicated that N applied at 4.9 kg ha^-1 every 7-d or 9.8 kg ha^-1 every 14-d reduces anthracnose severity compared to lower N rates, but less is understood about the impact of higher N rates on this disease.  A field study initiated in North Brunswick, NJ assessed the effect of high rates of soluble-N fertilization during the summer on anthracnose severity of ABG turf maintained at 3.2 mm.  N-fertilizer (NH₄NO₃) treatments, arranged as a RCBD with 4 replications, were applied at 4.9, 9.8, 14.7, 19.6 and 24.5 kg ha^-1 as a spray solution and irrigated. Each N treatment was applied every 7-d from 3 to 30 June and 23 July to 13 August 2009; the period of non-application (30 June and 23 July) was due to delayed disease development and a desire to avoid excessive growth.  Initially, N applied at 4.9 kg ha^-1 every 7-d had the greatest disease severity within the range of treatments studied.  As the season progressed, increased disease severity was observed in plots receiving the two highest N rates.  By 24 August 2009, the greatest anthracnose severity was observed in plots receiving N at 4.9, 19.6 and 29.4 kg ha^-1 every 7-d while the least amount of disease was observed in plots receiving N at 9.8 and 14.7 kg ha^-1 every 7-d.  Results indicate that inadequate and excessive N fertilization intensifies anthracnose severity on ABG putting green turf.