Light-Activated Sensor Controlled Sprayer (Weed Seeker®) for Cost-Effective Weed Control in Post-Harvest Wheat Stubble.

Field experiments were conducted at the Montana State University Southern Agricultural Research Center near Huntley, MT, in 2013, to evaluate effectiveness of light-activated sensor-controlled (LASC) sprayer (WeedSeeker^®) vs. conventional broadcast sprayer for weed control in post-harvest wheat stubble. A 1.5-m, ATV-mounted, spray boom was fitted with five LASC spray units equipped with flat-fan nozzles spaced 30 cm apart. Both of the sprayers were calibrated to deliver 94 L ha^-1 of spray solution at 276 kPa. Plots (2.5 m wide by 9 m long) were established following winter wheat harvest in the fall, and broadcast and LASC spray plots were established side by side for comparison. The weeds present at the test site were kochia and prickly lettuce. The study was established in a randomized complete block design with three replications for each herbicide treatment.  Savings in herbicide (plus recommended adjuvants) volume and cost using LASC technology vs. broadcast application were calculated. Kochia and prickly lettuce control did not differ between LASC and broadcast application for the POST herbicides tested. Paraquat (48 fl oz/acre), paraquat (32 fl oz/acre) + linuron (16 fl oz/acre), and saflufenacil (1.5 fl oz/acre) + 2, 4-D (16 fl oz/acre) provided greater control (92 to 100%) of kochia and prickly lettuce among all herbicide programs, 14 and 28 DAA. Glyphosate @ 64 fl oz/acre was more effective in controlling kochia (97%) and prickly lettuce (91 to 93%) compared with glyphosate at 22 and 32 fl oz/acre, applied postharvest in wheat stubble. Kochia control with pyrasulfotole + bromoxynil (15 fl oz/acre) (85 to 96%) did not differ from glyphosate (32 oz/a) alone or glyphosate (22 fl oz/acre) + dicamba (8 fl oz/acre) + 2, 4-D (16 fl oz/acre) (85 to 88%) 28 DAA. However, pyrasulfotole + bromoxynil was more effective (96 to 98%) compared with glyphosate + dicamba + 2, 4-D (80 to 85%) on prickly lettuce control 28 DAA. Control of kochia and prickly lettuce was least with dicamba (8 fl oz/acre) + 2, 4-D (16 fl oz/acre) (47 to 52%), followed by carfentrazone (2 fl oz/acre) + dicamba (8 fl oz/acre) (63 to 72%), and diflufenzopyr + dicamba (2 oz/acre) + 2, 4-D (16 fl oz/acre) (68 to 77%). Also, for each herbicide treatment, shoot dry weight response of kochia treated with LASC and broadcast spray did not differ, and was consistent with percent control ratings. LASC sprayer reduced the herbicide usage by 45 to 67%. Furthermore, there was 45 to 62% savings in herbicide (plus adjuvant) cost using LASC spray technology. This research suggests that LASC (WeedSeeker^®) sprayer would allow growers to apply higher rates of an herbicide and additional tank-mixtures to effectively control weed escapes or herbicide-resistant weeds in chemical-fallow or post-harvest wheat stubble, with savings in herbicide use and cost.