DETECTING BROWN PATCH AND DOLLAR SPOT DEVELOPMENT ON KENTUCKY BLUEGRASS BY SPECTROMETER SENSING AND TISSUE NITRATE-N MONITORING

D. Li, R. Smith, K. Kinzer, S. Neate
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.
Li, D., Smith, R., Kinzer, K. and Neate, S. 2008. DETECTING BROWN PATCH AND DOLLAR SPOT DEVELOPMENT ON KENTUCKY BLUEGRASS BY SPECTROMETER SENSING AND TISSUE NITRATE-N MONITORING. Acta Hort. (ISHS) 783:547-558
http://www.actahort.org/books/783/783_56.htm
nitrogen, disease forecast, prediction model
English

Acta Horticulturae