Plasticulture
Plastic Color and
Composition Effect on
Earliness, Yield and
Quality of Bell Peppers
The Tomato Magazine
October 2005
A California study looking at the use of plastic mulches on bell peppers
showed significant yield increases and earlier production over non-treated
plots.
Reporting their work at Plasticulture ’05, held March 5-8 in Charleston,
S.C., Richard Molinar, Don May and Blaine Hanson of the University of California
Cooperative Extension, Fresno, Calif., noted that the best yield was with the
Natural 11 treatment. The treatment yielded 559 cartons per acre in one pick
(or 659 cartons per acre if two picks had been done) over the non-plastic treatment.
California’s vegetable industry is the largest and most diverse in the
world. Plastic mulches are used commercially in peppers and other crops for a
variety of reasons, although, overall, the total usage of plastic remains quite
small. Plastic is generally used to increase yield, control weeds, protect fruit
from rain and soil contact and promote earlier harvest. This particular study
evaluated different colors and formulations of plastic in bell peppers and cantaloupes.
The bell pepper study was conducted in 2003, according to Molinar, with the researchers
evaluating different colors of plastic mulches for earliness, weed control, yield,
fruit quality and plastic longevity.
The bell pepper beds were 66 inches wide. One hundred pounds of 11-52-0 was applied
pre-plant in the bed and high flow drip tape was laid two inches deep and in
the center of the beds. The Jupiter variety was transplanted on March 3, with
holes spaced 12 inches apart down the row and two rows per bed 18 inches apart.
Nitrogen applications started on April 1 with 12 weekly applications of 20 lbs.
of N per acre using UN32. A total of 252 lbs. of N was applied throughout the
season.
The bell peppers were hand harvested one time when approximately one-third of
the fruit was red or chocolate colored. They were graded into red, marketable
green, small green and culls. The culls were rotten or deformed peppers of any
color or size.
Significant Yield Increases
The Natural 11 plastic treatment yielded significantly higher than almost all
of the other plastic except the Natural 8, the research team reported. The
treatments that yielded significantly better than the non-plastic plots were
the Natural 9 and 10, Olive 19, Silver/Black 17 and Black 6, 1, 4, 7 and
5. The plastics that did not yield significantly higher than the check were
Silver 14, Blue 13, White/Black 18 and Black 3. The treatments that performed
significantly poorer than the non-plastic treatment were White 15 and 16
(see Table—Estimated Yield).
An estimated total yield, if there was a second harvest, was made by adding
the weight of the small fruit multiplied by a factor of 2.5 to the yield of
the first harvest. This did not result in any significant yield changes between
treatments. (See Table—Estimated Yield).
The check treatment yielded the highest percentage of green fruits and the
lowest percentage of red fruits, but these differences were not significant.
This indicates that the use of most plastics resulted in earliness of fruit
maturity, the researchers said. The percentage of culls was not affected by
plastic treatments (See Table—Fruit Color and Size).
The average weight per fruit was not significantly different in the small and
green fruits, the team added. There was a significant difference in the average
weight of the red fruits between plastic treatments but no specific color was
best (see Table—Weight/Pepper).
The Incentive Is There
So what were the conclusions of the study? Plastic mulch resulted in significant
yield increase and earlier production over non-treated plots, Molinar and
colleagues said. The best yield was in the Natural 11 treatment yielding
559 cartons per acre in one pick or 659 cartons per acre in two picks over
the non-plastic treatment.
One word of caution: It would only be economical to use this treatment, the
report stressed, if weeds were chemically controlled underneath the natural
plastics. Higher yields and earlier fruit maturity may have occurred in the
natural plastics if the weeds were chemically treated early and/or there was
no plant disturbance during hand weeding. Otherwise, it would be more economical
to use the Olive 19, Silver/Black 17 or Black 6 treatments. Weeds under the
natural plastic were pulled twice by hand reach through the planting holes.
In the other plastic colors it was difficult to see the weeds so only the weeds
that came through the holes were removed. The weeds were most aggressive in
the white plastic treatments.
Funding for these trials was provided by Ampacet Corp. to evaluate the deterioration
of the plastic in different areas of the world. Plastic samples were collected
from the treatment row ends of plots that were left unplanted. Under the plastic
treatments with no crop there was little weed growth during the nine-month
test period for the three years of evaluation (three years for cantaloupe and
one year for bell peppers). Some weeds did germinate but died shortly thereafter.
Only in the white plastics did weeds grow more than several inches before dying.
For more information on these trials, including the particular plastic formulations,
contact Richard Molinar at rhmolinar@ucdavis.edu or Brionna Barber at Ampacet
(bbarber@ampacet.com).
© 2006 Columbia Publishing
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