Detecting brown patch and dollar spot development on Kentucky bluegrass by spectrometer sensing and tissue nitrate-N monitoring

Detecting brown patch and dollar spot development on Kentucky bluegrass by spectrometer sensing and tissue nitrate-N monitoring

Nitrogen affects all aspects of turf quality including color, density, stress tolerance, and susceptibility to diseases. Soil analysis usually does not include the available N in soil because it changes rapidly and the test is very time-consuming. Clipping yield is often used by turf managers as an indicator of N sufficiency. The primary objective of this study was to investigate if there was a correlation between Nitrate (NO3 -)-N concentration in grass tissues and disease index for dollar spot and brown patch in Kentucky bluegrass (Poa pratensis L. 'Moonlight'). A second objective was to test the feasibility of using NO3-ion specific electrode and/or spectral radiance to monitor disease severity. N amounts (0, 50, 100 and 200 kg ha-1) were main plots and disease inoculations were subplots in trials conducted in 2004 and 2005. The normalized difference vegetation index (NDVI) from a spectral radiance measurement was very sensitive to disease stress level and N status. In both experiments, shoot and leaf NO3-N concentrations were significantly different among the N fertilization amounts in 70% of the sampling dates. In 2004, correlation coefficients between tissue NO3-N and N application amounts were 0.07 to 0.27 and 0.03 to 0.87 for leaf and shoot, respectively. In 2005, the correlation coefficients between tissue NO3-N and N application amounts were 0.30 to 0.51 and 0.29 to 0.78 for leaf and shoot, respectively. Dollar spot severity was negatively correlated to N nutrient levels in shoots and leaves with correlation coefficients as -0.60 and -0.61, respectively in 2004. Correlation coefficients between dollar spot severity and N nutrient levels in shoots and leaves were -0.87 and -0.81 for 3.8-cm mowing height, and -0.79 and -0.61 for 7.8-cm mowing height, respectively. Tissue NO3-N levels have potential to be used in dollar spot forecasting models in combination with environmental condition monitoring. Brown patch disease was less affected by tissue N levels but rather by microenvironment in the turf canopy.

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