While lettuce is an intensively managed specialty crop for which there is little tolerance for weeds, the herbicide benefin (Balan®) is commonly used in preplant and preemergence applications to control weeds during lettuce stand establishment. In fields with high clay and low organic matter contents, considerably more of the herbicide is required for adequate weed control than in soils with higher sand contents where excessive herbicide rates can injure young lettuce roots. A three year effort involving variable rate application (VRA) of Balan® was conducted on three, 10 ha grower-cooperator leaf lettuce fields in Yuma, AZ (USA) each consisting of three distinct soil textures and application rates; a clay (2.8 kgai/ha), a loam (2.2 kgai/ha) and either a sandy loam or loamy sand (1.7 kgai/ha). The effectiveness of VRA was determined by comparing conventional applications at the standard rate of 2.2 kgai/ha and quantifying lettuce injury, yields at harvest, and overall weed control. Site-specific placement of Balan® resulted in over 30% reduced lettuce seedling injury in loamy sand textured soils with 35% lower application amounts than using conventional methods; weed control was similar among all treatments. As over 40% more marketable lettuce was demonstrated in sandy loam textures using VRA, the application shows promise for weed control in leafy greens where non uniform soil textures show a severe challenge to production.
Key words: Benefin, variable rate application, variable rate application, precision agriculture, soil texture, soil uniformity, lettuce, site specific, herbicide, weed control, crop injury.
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