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Mechanized Weeding System Coming?

The Tomato Magazine
August 2006

By Lisa Lieberman

Hand labor, as most growers know, is one of the costliest and more difficult to find resources in farming. In tomatoes, hand weeding and herbicide application are a large part of a grower’s input costs. Sometime within the next few years, though, there may be a new mechanized weeding system available to growers that will save them hundreds of dollars per acre.

Over the past three years, David Slaughter, a researcher at the University of California at Davis, has been working on perfecting a precision weed control system that can tell the difference between weed and tomato seedlings in the field. The mechanism is comprised of a hyper spectral camera with over 1,000 color bands and many more detailed color measurements than a normal camera.

The ultimate design for the system would include some protective housing for the camera which would then be pulled behind a tractor down the tomato rows. The camera would take several dozen photos per second and detect the weed seedlings from the tomato plants down the seedlines of the field. On the back of the mechanism would be several mounted miniature hooded sprayers in between the rows spot spraying the weeds, leaving the tomato plants and everything else in the field untouched.

“The sprayers follow right behind the camera system that’s making a map of the seedline, and then the precision spot sprayer looks at the map and sprays exactly where the weeds are,” Slaughter says.

In addition to saving famers money in herbicide treatements, the spot sprayer also has the potential to ease some of the labor shortage problems growers have been experiencing.

“ This could have a big impact politically on the labor isue,” says Slaughter. “The fact that Congress hasn’t passed a guest worker bill yet means there’s going to be more potential labor shortages, especially if we continue beefing up the border.”

One of the biggest challenges in perfecting the spot sprayer is getting the camera to distinguish between tomato plants and nightshade weed species. Nightshade weeds appear fairly similar to tomato plants in terms of coloring and shape, Slaughter points out.

“When the nightshade plants come out of the ground, they are fairly distinct, but as they grow and leaves start to overlap, it becomes a challenge to identify them because you can only see parts of the leaves,” Slaughter says. “The human eye is good at pattern recognition and seeing shapes even if parts of the leaves are hidden. But it’s a lot more challenging for a computerized system to see the objects if only parts of them are showing.”

Despite its drawbacks, the spot sprayer system is about as accurate as hand crews are, Slaughter says. According to studies, hand crews are about 85 percent accurate in detecting and killing weeds, while the spot sprayer is 80 to 90 percent accurate.

Slaughter is working on boosting the accuracy of the spot sprayer by adding more detailed color capabilities to the camera. When the spot sprayer becomes commercially available, it will enable growers to use nonselective herbicides, such as Round-up, instead of selective herbicides. Whenever selective herbicides are used weed resistance problems tend to develop more quickly.

“The problem with these selective herbicides is that there aren’t that many options, so if a weed such as nightshade builds up resistance, it becomes less effective over time,” Slaughter says.

But aside from using herbicides to kill weeds, there are other possible controls, adds Slaughter. One is the use of a mechanized knife attached to the back of the precision weeding mechanism.

“There were systems like this developed in the ‘60s and ‘70s for automatic thinning. With such systems you could pair up the detection system with the knives, and you wouldn’t have to use any chemicals,” Slaughter explains.

Tom Lanini, a weed ecologist at the University of California at Davis, believes the precision weed seeker has “immense implications for growers.”

“Most applications of chemicals (about 65 percent)—insecticides, fungicides, herbicides and pesticides?are for weed control,” he notes. “With insects and diseases, you may have certain ones that will or won’t occur in a given year, but you’re always going to have weeds, no matter what. And in crops like tomatoes and peppers, where you have to do a lot of hand weeding and the cost of labor is going up, there’s enormous potential to save farmers money.”

Once they become commercially available, the systems are expected to cost about $10,000, Lanini says.

“In tomatoes, this system can save growers well over $100 per acre. So, if you have 100 to 200 acres, you could get your money back pretty fast,” Lanini stresses.
Nonselective chemicals, such as Round-up, that farmers might use with a precision weeding system could also be much more effective than some of the traditional selective herbicides farmers use, Lanini believes.

“Most of the time, farmers use selected herbicides, but nothing works quite as well as chemicals that control everything,” the researcher says.

Typically, farmers are reluctant to use Round-up in their fields because it’s difficult to keep the chemical off of the tomatoes. “But with a system like this, it wouldn’t actually spray the chemicals; it would be more like a squirt gun shooting a tiny spray out of a micro-syringe that hits a very precise target without even hitting the soil,” Lanini explains. “It would be like a laser beam going in and out and hitting the weeds and missing the crop.”

© 2006 Columbia Publishing

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