Anthracnose Severity of Annual Bluegrass Putting Green Turf as Affected by Summer Soluble N-Fertilization.

Adequate N fertility to sustain moderate growth has been previously reported to reduce anthracnose (Colletotrichum cereale Manns) severity on annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] putting green turf.  In 2007, a study was initiated in North Brunswick, NJ to determine the effect of variable rate and frequency of soluble-N fertility during mid-season on anthracnose severity of annual bluegrass putting green turf maintained at 3.2 mm.  Treatments of 4.9 kg ha^-1 every 1, 2, 4, and 8 wk and 9.8 kg ha^-1 every 2 and 4 wk were applied as a foliar spray.  The latter two treatments were included to determine if disease suppression could be obtained by increasing intervals between sprays while increasing the rate of application.  The date of initiating mid-season fertilization (mid-May vs. mid-June) was also evaluated.  Nitrogen applied at 4.9 kg ha^-1 every 7-d or 9.8 kg ha^-1 every 14-d had the greatest percent reduction in anthracnose severity throughout both years and the N response was linear within the range of treatments studied.  Nitrogen applied at 4.9 kg ha^-1 every 14-d was the lowest N treatment to reduce disease severity, and mid-season soluble-N fertilization at 4.9 kg ha^-1 every 28- or 56-d had the greatest percent anthracnose severity each year.  Initiating N fertilization before symptom expression (mid-May) reduced anthracnose severity compared to fertilization begun at the onset of disease (mid-June).  Mid-season applications of soluble-N are an effective tool to reduce anthracnose severity on annual bluegrass putting green turf.