Equipment for application of postemergence directed sprays for weed control in narrow-row no-tillage soybeans

A field study was conducted in 1983 at The University of Tennessee Milan Experiment Station to assess the potential for using tractor-mounted postemergence directed spraying equipment for weed control in no-tillage soybeans (Glycine max) planted with 20-inch row spacing in wheat (Triticum aestivum) stubble. Six commercial or experimental directed sprayers either designed exclusively for or adapted to use in 20-inch rows were used to apply a tank mix of linuron and 2,4-DB in 12-inch soybeans.

Crop injury due to both mechanical damage and chemical contact were subjectively assessed for each system. Sprayers producing the most injury (up to 40 percent) had some misaligned machine assemblies or had limited capability for adjustment of row protection shielding. Two shielded sprayers resulted in crop injury ratings of 10 percent or less.

A single herbicide application with any of the sprayers gave good control (80 to 88 percent) of cocklebur (Xanthium pensylvanicum) with no significant differences among applicators. Control of large crabgrass (Digitaria sanguinalis) was poor (40 per cent) with all sprayers primarily because the grass was severely drought stressed at the time of application.

Drought conditions during the growing season resulted in abnormally low yields. No significant differences in yields were shown among the treatments. However, yields in sprayed plots tended to be greater than those from untreated plots.