Influence of Irrgation Management on Anthracnose Severity of Annual Bluegrass.

            Irrigation can affect vigor of putting green turf, and anthracnose (Colletotrichum cereale Manns) disease is more severe on stressed plants.  The objective of this trial was to evaluate the effects of irrigation on anthracnose severity of annual bluegrass [Poa annua L. f. reptans (Hausskn.) T. Koyama].  This study was initiated in 2006 on a 5-yr old annual bluegrass turf mowed daily at 3.2-mm using a randomized complete block design with four replications.  Irrigation treatments of 100, 80, 60 and 40% of reference evapotranspiration (ET_o), based on the Penman-Monteith equation, were applied daily to 2.4 by 2.4-m plots.  Individual plots were syringed (≤ 2.5-mm water) when wilt stress was visible.  Pesticides that did not affect anthracnose were used to control insects and other diseases.  Anthracnose severity was assessed every 7 to 10 days from mid-June through mid-August.  Drought stress (40% ET_o) increased anthracnose in both 2006 and 2007; anthracnose was less severe under 60% ET_o irrigation and irrigating at 80% ET_o reduced severity compared to 60% ET_o.  Irrigating at 100% ET_o initially reduced anthracnose severity compared to 40% ET_o; however, 100% ET_o resulted in similar disease severity by the end of the 2006 season.  While irrigating at 100% ET_o did not increase disease severity in 2007, 100% ET_o plots had poor turf quality in both years similar to 40% ET_o irrigation.  Thus, irrigation to avoid repeated wilt stress should decrease anthracnose severity on annual bluegrass.