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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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