Influence of nutrient management and soil pH on anthracnose severity of annual bluegrass putting green turf
Creators: name: Schmid, Charles J.
Publisher: name: No Publisher Supplied
Year: 2016

description: Anthracnose (Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman) is a fungal disease of annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama; ABG] turf, which can be intensified when abiotic conditions weaken turfgrass plants. Five field trials conducted from 2009 to 2015 evaluated the effects of N program, soluble N rate, N source, K source and rate, and soil pH on anthracnose severity of ABG maintained as putting green turf. Soluble N rate applied during midseason had the greatest influence on anthracnose severity. Granular N rate and season in which the majority of granular N was applied also influenced disease severity but to a lesser extent. Soluble N applied at 73 kg N ha-1 yr-1 in combination with moderate rates (147 or 220 kg N ha-1 yr-1 ) of granular N applied during the spring resulted in the greatest reduction in disease severity. Further analysis of the influence of soluble N rate on anthracnose severity found that higher rates (14.6 to 24.4 kg N ha-1 wk-1 ) of soluble N can be applied from late-spring through early-summer to reduce disease severity, but as the summer progresses moderate (9.8 kg N ha-1 wk-1 ) to low (4.9 kg N ha-1 wk-1 ) rates of soluble N should be applied to avoid excessive rates of N increasing disease severity. Playability (i.e. ball roll distance) of ABG turf was reduced by rates of soluble N applied at ≥ 14.6 kg ha-1 wk-1 compared to N applied at 4.9 kg ha-1 wk-1 . Basic N sources (potassium nitrate and calcium nitrate) applied at 4.9 kg N ha-1 every 7-d reduced disease severity compared acidic N sources (ammonium nitrate and ammonium sulfate) applied at the same rate and frequency; however, when N was applied at 4.9 kg ha-1 every 14-d, disease severity was greater and few differences were seen among N sources. Potassium (K) fertilization reduced anthracnose severity regardless of K rate or K source. Critical soil K and leaf K concentration values affecting anthracnose severity were calculated to range from 43 to 70 mg kg-1 (Mehlich 3) and 19.3 to 23.1 g kg-1 , respectively, using nonlinear regression models (Cate-Nelson, linear plateau, and quadratic plateau). Plots with moderately acidic soil (pH &lt; 5.5) and deficiencies in extractable soil Ca increased disease severity compared to plots with neutral (to slightly acidic) soil pH and adequate soil Ca. Optimum soil pH for reducing anthracnose severity and maintaining acceptable turfgrass quality of ABG putting green turf was between pH 6.0 and 6.5 and critical soil Ca concentrations ranged from 392 to 825 mg kg-1 . It is not clear whether acidic soil conditions and/or deficiencies in extractable Ca caused increased anthracnose severity and a reduction in turfgrass performance. Taken together, these studies clearly indicate that best management practices that include proper plant nutrition and possibly modification of soil pH are effective at reducing anthracnose severity and should be incorporated into an integrated disease control program.