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Zap weeds and sweep streets in one pass

Street sweepers apply herbicides for double-duty savings.

Publication date: March 8, 2012

By Leslie Drahos

Meeting two needs with one deed makes Douglas Grider, public works superintendent of Lakeport, Calif., a shrewd manager. The City has combined two tasks — cleaning streets and controlling curbside weeds — into one smooth drive-by activity.

An herbicide spray system called WeedSeeker has been installed on the back of Lakeport's sole street sweeper, which scrubs all 32 miles of the City's streets each week. Here's how it works: Seconds after the sweeper cleans the gutter, the WeedSeeker — which is mounted behind the curbside wheel well — follows up with a metered spray of herbicide if it senses plants growing in cracks and joints around curbs, gutters, and sidewalks.

The City of Lakeport, Calif., has mounted two WeedSeeker units on the rear of its only street sweeper to control plants in gutters, curbs, and sidewalks with targeted herbicide applications.

One control panel mounted near the driver can operate up to 40 WeedSeeker units.

Before using the WeedSeeker, the City applied herbicides in several ways, depending on the location to be sprayed. In one instance, workers in a small pickup truck equipped with a tank used a stationary boom with nozzles to apply herbicides to bare ground, pavement, and weedy areas. In other parts of town, where vehicles were parked along roads, one person drove the truck, while the other had to get out and manually spray.

"Now some people think if a little bit [of herbicide] is good, then a whole lot more is better," Grider says. "With that mentality, 250 gallons of herbicide can be gone after only five or 10 blocks. The really great thing about this new system is you take away that variable completely. It does away with someone walking along or driving along and having to think when to turn the spray on or off and guessing how much is enough." More automated application also helps ensure herbicides are used at rates that follow label directions.

Made by Trimble Navigation, each WeedSeeker unit has a circuit board with a built-in LED light source, reflected light detector, electromagnetic valve, and spray nozzle, all housed in a nylon casing with an integrated stainless-steel bracket. Each unit has a 12-inch field of view.

The sensor surveys the ground for the presence of chlorophyll. If a plant is detected, a valve activates the nozzle to spray a controlled amount of herbicide.

"So you are taking two guys in a pickup truck and an application system and you replace them with a vehicle that you already own and one employee already doing another task, which is sweeping streets," says Grider. "Now he's also taking care of weed control on the curb, gutter, and front edge of the sidewalk."

A sensor can detect weeds as small as a dime, and spot and spray at speeds of up to 10 miles per hour. Coverage may be widened by adding more units. Each unit runs independently of others. The control panel manages up to 40 units, a volume often used for large-scale agricultural spraying. The devices may be angled to spray weeds under open guard rails and along ditches, or to reach over sidewalks.

Grider estimates the City will recoup its investment in three years from savings in crew hours, chemicals, and equipment use.

"I am not sure about other parts of the country, but we have to stretch every penny as far as we can," he says. "My staff has dropped 50 percent from eight years ago. So if you have two guys just spraying weeds, then you don't have two guys out patching potholes or repairing sidewalks."

Leslie Drahos is a freelance writer in Sagamore Hills, Ohio.

A short video shows how the WeedSeeker works on city streets.