February 2022 - 9

Photo 4: The Titan tractor-mounted in-row robotic weeder made by FarmWise.
EASY TO USE DUAL ACTIVE
GROUP M5 & 22
removed 98% of in-row weeds and
reduced hand weeding time by about
half compared to between-row tractor
cultivation (although in another pass
it reduced weeds by 52% - again,
results are variable). The Dino was
fitted with finger weeders, and it
removed 61% of weeds compared to
between-row tractor cultivation that
removed 41% of weeds.
Fennimore was impressed with the
ability of these machines to operate
accurately in fields with high weed
densities. In July, there was a lettuce
field overrun with purslane (photo
5). He thought they had to cancel
the trial because the computer could
not tell the difference between the
lettuce plants and weeds, but the Stout
company figured it could do it. The
standard tractor cultivation effectively
removed none of the weeds in the
row, but the Stout removed 76% of
in-row weeds. With the high weed
density it took a long time to make
it through the field - the standard
tractor cultivation required 78 hours
per acre whereas the Stout needed 30
hours per acre. Although in general,
growers around Steve have found that
tractor-mounted robotic weeders can
cultivate a 10-acre field in 8-10 hours.
Fennimore said that as an Extension
specialist he cares about production
costs; even if these robotic weeders
work wonders, if they increase
production costs by too much, they
aren't good for growers.
He cited a study comparing the costs
of robotic weeders to hand weeding
in lettuce (Tourte et al., in review).
They figure that it costs on average
$161 per acre to hand weed lettuce.
Then they figured the costs for three
different types of tractor-mounted
in-row robotic weeders - they varied
from $166-$204 per acre (including a
tractor, operator, cost of machine and
maintenance). Use of these machines
could reduce hand weeding costs
to $100 per acre, but overall costs
for weed control using the robotic
weeders ranged from $266-$304
per acre.
This means that using robotic
weeders costs more than hand
weeding. So why are some growers
MULTI-SITE EFFECTIVENESS
Photo 5: Lettuce overrun with purslane,
after a traditional between-row
cultivation run. The camera-guided
machine was able to pick out the
lettuce plants in this dense weed cover.
in California adopting these robotic
weeders?
Fennimore did some research
and thinking to figure out why. He
found a survey of CEO's asking them
why they want to adopt technology
(Economist, 1/16/21). They said
that machines can reduce risk
(fewer people get hurt), be more
reliable than employees and help
with making costs more predictable.
Additionally, herbicides are showing
diminishing returns and fewer young
people aspire to be hand weeders.
Because these robotic weeders
require investment (a standard Stout
model is $350,000) some companies
contract out the use of the machine -
much like how you would hire out a
custom sprayer or harvester.
For now, these autonomous robotic
weeders and tractor-mounted in-row
robotic weeders are concentrated in
our nation's largest vegetable-producing
areas in Southern California and
Arizona. But I spoke with the CEO
of Stout, Brent Shedd, and he tells me
that they have machines in Florida
and Georgia, and interest from the
Midwest. So we will see how these
robotic weeders spread. VGN
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February 2022

Table of Contents for the Digital Edition of February 2022
