Due to a lack of effective selective, post-emergence herbicides, most vegetable crops are hand weeded following cultivation to remove in-row weeds.  This operation is costly and finding labor to perform the task has become increasingly difficult.  An alternative is to use automated/robotic machines for in-row weeding. These machines have been around for quite some time; the first “modern” units were commercialized in 2008. Since then, at least six companies have introduced machines and offer units for sale and/or automated weeding as a service in Yuma, AZ. 

Despite these innovations and efforts, adoption of automated weeding machines has been limited. One reason for this is that weed control is only partial, and follow up hand weeding is often necessary. All commercialized automated weeders utilize metal blades that move in and out of the crop row to cultivate weeds between individual crop plants as the machine moves through the field. As such, soil disturbance is high and weeds close to crop plants cannot be effectively removed without injuring crop plants. In a two-year study (Lati et al., 2016), we found that mechanical automated weeders removed about 2/3rds of in-row weeds.  The majority of uncontrolled weeds (~ 1/3rd) were observed to be within about 1” of the crop plant. 

To address the lack of precision of current automated weeding machines, we developed two high speed, centimeter scale resolution sprayers to spot apply herbicides to weeds with minimal off-target spray while traveling speeds that are viable for commercial farming operations (2 mph). The first is a high precision (sub-centimeter scale resolution) sprayer designed for spot spraying cotyledon stage weeds in leaf lettuce crops. The second is a spray assembly designed for controlling in-row weeds in vegetable crops that are close to crop plants (1-cm scale resolution). We tested the device in 2019 in the laboratory and found that weed control efficacy was greater than 95% (3 species), percentage of off-target spray was less than 3% and no crop injury was observed. A link to action videos of the device in action is provided at the link below. Future work includes seeking funding, and industry partners for integrating the devices with imaging systems to develop a high precision, automated/robotic weeding machine for vegetable crops.

Cited reference:

Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.

High Speed Centimeter Scale Resolution Sprayers for Precision Weed Control – Video Link: https://www.youtube.com/watch?v=TFja9FmVjJI

To contact Mark Siemens go to: siemens@cals.arizona.edu