Nitrogen Fertilization Programming Effects On Anthracnose Disease of Annual Bluegrass Putting Green Turf.

Nitrogen fertilization affects the development of anthracnose disease (caused by Colletotrichum cereale Manns) of annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] putting green turf; however, a more comprehensive understanding of N management strategies is needed. The objectives of this 24 mo field study were i) to evaluate N rate effect of late- or early-season granular-N fertilization on anthracnose severity and ii) to determine whether granular-N fertilization altered the effect of frequent, low rate soluble-N fertilization during mid-season on anthracnose. The study, conducted on annual bluegrass turf maintained at 3.2 mm, was initiated autumn 2008 in North Brunswick, NJ. Treatments were arranged as a 2 x 3 x 4 factorial with three replications. The first factor was the season in which the majority (67%) of granular-N fertilization was applied: autumn and spring. The second factor was the annual N rate of granular fertilization: 73, 146 and 219 kg ha-1. The third factor was the frequency/rate of soluble-N fertilization during the summer; soluble-N treatments were sprayed at 4.6 kg ha-1 of N at the frequencies of 0, 1, 2 or 4 weeks from mid-May through August (16 weeks). Spring granular-N fertilization reduced disease severity compared to autumn on all but two rating dates during the study. The annual granular-N fertilization rate of 219 kg ha-1 had less disease (8 of 12 ratings) than plots that received lower rates. The interaction between season and granular-N rate (5 of 12 ratings) indicated that reduced disease severity due to spring N-fertilization compared to autumn was only evident at the annual granular-N rates of 146 and 219 kg ha-1. Summer soluble-N applied at 4.6 kg N ha-1 week-1 had the greatest reduction in anthracnose severity compared to less frequent soluble-N treatments (10 of 12 ratings).