PCC July-August 2020

Figure 3. (a) Topical marker on lettuce plants.
A new method of crop and weed differentiation
called “crop signaling” is presented
in the research “Crop Signaling
for Automated Weed/Crop Differentiation
and Mechanized Weed Control in
Vegetable Crops” by Raja et al. 2019 out
of UC Davis. It is based on the idea that
the identity of the crop is known with
certainty when it is planted, whether
transplanted or seeded. Thus, if the crop
has a marker or signal that an IC can
reliably detect, then the IC would recognize
the signal and protect the crop.
Plants without the signal, i.e., weeds,
would not be protected and would be
removed by the IC. The objective of this
work was to test a crop signaling system
for crop detection accuracy and weed
control efficacy by an IC in lettuce and
tomato.
Marking System Descriptions. Two
methods of plant signaling were tested,
physical plant markers and topical
markers. Biodegradable straws coated
with a fluorescent marker were used as
the plant markers in this study (Figure
1). The straws were then placed next to
tomato seedlings in the planting trays
and then transplanted together (Figure
2).
The topical marker used on plant foliage
was green or orange fluorescent water-based
paint (Figure 3a,b). A paint
sprayer was used to apply the topical
marker to lettuce foliage and tomato
seedlings prior to planting, while they
were in trays. Another method was to
spray the marker onto tomato stems as
they were transplanted (Figure 4).
Intelligent Cultivator. The IC used
in this research was developed at the
University of California, Davis. It uses
a machine vision system specifically
Figure 3. (b) Spray application of topical marker on crop plants.
designed to detect the physical labels
and topical markers on the crop (Figures
5&6, see page 14). Weed control
was done by mechanical knives, which
the IC opens to avoid the marked crop
plants and closes (Figure 6, see page 14)
to uproot weeds in the intra-row space.
Field Trials
Eight field trials in tomato at Davis, Calif.,
and six in lettuce at Salinas, Calif.,
were conducted during 2016-2018.
Tomato. Field trials in processing
tomatoes were located on a silt loam soil
on the UC Davis vegetable field crops
research station near Davis. The tomatoes
were seeded in trays and kept in a
greenhouse for 45 to 60 days until they
were about 10 inches tall. Tomatoes
were transplanted into 60-inch beds at
15-inch spacing in a single center row.
Two tomato trials were carried to yield.
Plant labels were added to seedling
trays prior to transplanting (Figure 1)
or the topical marker was applied to
trays of tomato seedlings as described
above (Figure 4). Tomato transplants
were marked with paint 4 inches above
the soil line. About three weeks after
planting, all plots were cultivated with
a standard mechanical cultivator which
only removed weeds outside the plant
line. The standard cultivator left a
7-inch non-cultivated band centered on
the crop row.
Weed densities by species were measured
before and after cultivation in
four 7-inch-wide (centered on crop row)
by 20-foot-long sample areas randomly
placed along the length of the plots. The
time required by a laborer to hand weed
the 20-foot areas was recorded. Two
tomato trials were maintained until
Continued on Page 14
Figure 1. Plant labels in tray of tomato
seedlings prior to transplanting. The
labels and tomato plants were
transplanted together in the field.
Figure 2. Holland transplanter with
butterfly transfer fingers used for
transplanting plant labels and tomatoes
together.
Figure 4. Topical marker sprayed
on tomato transplants by applicator
mounted on the transplanter during
the process of transplanting.
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