Field experiments were conducted for 3 yr to determine the effect of various biological and physical factors on the operation of the weed-sensing Detectspray system. Plant detection is achieved by sensors measuring differential reflectance of red and near-infrared wavelengths of light from green plants, crop residues, and soil. Weed detection was greatly reduced 70 to 80 min after sunrise and before sunset when operated at lat 50°N because of reduced solar irradiance. Tall, dense-standing crop stubble limited detection of small weeds at the soil surface. Weed detection varied with plant species. Canola with three to four leaves consistently was detected, but wheat or green foxtail usually required five to six leaves to be detected. Small weeds were detected if present at densities greater than 70 plants m−2. Growers and commercial applicators need to be aware of the limitations of the Detectspray system to use it effectively to control weeds with concurrent reductions in herbicide use.

Studies to predict pesticide fate often lack measurements of model input parameters. Using independent data sets and understanding how soil properties affect herbicide retention and degradation may result in more accurate prediction of herbicide fate. We conducted laboratory studies to determine the influence of soil properties on atrazine adsorption and degradation. These data will be used in a separate study involving a pesticide fate model. Atrazine adsorption and desorption isotherms were constructed for six soil depths of a Hastings silty clay loam (fine, montmorillonitic, mesic Udic Argiustoll) using batch equilibration. The Freundlich adsorption constants (log Kf) ranged from 0.38 (60 to 90 cm) to 2.91 (0 to 30 cm). Adsorption was higher in the low pH, high organic matter-containing surface soil compared to the lower soil depths. Multiple regression of the adsorption constants against selected soil properties indicated that organic matter content was the best single predictor of atrazine adsorption (R2 = 0.98) followed by soil pH (R2 = 0.82). Combining organic matter and cation exchange capacity in the model produced the lowest Cp statistic (2.33) and highest R2 value (0.99). We observed hysteresis in atrazine adsorption–desorption isotherms by higher adsorption slopes (1/n)ads compared to desorption slopes (1/n)des. Soils that adsorbed more atrazine also desorbed less atrazine. Desorption correlated negatively with organic matter content and positively with soil pH. Atrazine degradation after 84 d of incubation generally decreased with increasing depth. The first-order degradation rate was highest 0 to 30 cm deep (0.0187 day−1) and lowest 270 to 300 cm deep (0.0031 day−1). Atrazine degradation was faster in soil treated annually for 12 yr than in soil with no previous atrazine history (p = 0.01).

The antifungal activity of the herbicides bialaphos and glufosinate, the active moiety of bialaphos, was assessed. Bialaphos showed a higher level of in vitro antifungal activity against Rhizoctonia solani, Sclerotinia homoeocarpa, and Pythium aphanidermatum than glufosinate. Glufosinate suppressed the mycelial growth of R. solani and S. homoeocarpa, but it had no inhibitory effect on P. aphanidermatum up to the highest concentration in our testing regimes. Various concentrations of bialaphos solutions were applied to transgenic, bialaphos- and glufosinate-resistant creeping bentgrass inoculated with fungal pathogens. Bialaphos applications were able to significantly reduce symptomatic infection by R. solani and S. homoeocarpa on transgenic plants. Bialaphos significantly inhibited P. aphanidermatum, but not to the same degree that R. solani and S. homoeocarpa were inhibited. These results indicate that bialaphos may provide a means for the simultaneous control of weeds and fungal pathogens in turf areas with transgenic, bialaphos-resistant creeping bentgrass.