Mechanized Weeding System Coming?
The Tomato Magazine
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
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
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
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
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
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
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
sprayer becomes commercially available, it will enable growers to
use nonselective herbicides, such as Round-up, instead of selective
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
Tom Lanini, a weed ecologist at the University of California at Davis,
believes the precision weed seeker has “immense implications
“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
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
Nonselective chemicals, such as Round-up, that farmers might use
with a precision weeding system could also be much more effective
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
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
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