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Brite'Nup High-Density Metalized Polyethylene Reflective Plastic Enhancing Color With Reflective and Colored Mulches Excerpts from an article in the June/July 1997 issue of California Grower Magazine, authored by Harry Andris and provided here by permission of the author. Harry Andris is a UC Cooperative Extension farm advisor in Fresno County. Over the past four years, many growers have begun to experiment with the use of reflective mulches to enhance tree fruit color. This concept of reflecting light into the orchard canopy came about through some of the research I performed as farm advisor for the UC Cooperative Extension in Fresno County. The initial field studies were conducted in a Fuji apple orchard owned by Tad, Gary, and Mits Kozuki, owners of Kozuki Farming in Parlier, California. The Fuji orchard used in these first field studies (1993-1994) was grown on a Lincoln Trellis system, which helps to reduce sunburn in the hot San Joaquin valley, but also limits the amount of sunlight reaching the apple surface. The concept of reflecting light up and onto this fruit seemed natural. Red color development in tree fruit, whether in apples, nectarines, cherries, pomegranates, or other fruit, is triggered by a chemical reaction which changes the red pigment precursor cyanidin to ideain, the red pigment. This shift takes place if the enzyme that catalyzes this reaction is at the right temperature (64.4°-77°F). Temperatures lower than 77°F promote color development. Also important are high light interception and high photosynthetic activity. High fruit tissue potassium levels also improve red pigment formation, and low nitrogen levels are important, since if there are high nitrogen levels in plant cells, the phenylpyruvate will be converted to proteins and used in growth, not in pigment precursor formation. When using reflective mulches to enhance the coloring process, the first observable color change is in the background color, which can be seen in as few as 4 days after the materials are placed in the field. From a practical point of view, the best red color enhancement occurs if the mulches are spread in the orchard 3 to 4 weeks prior to harvest. Over the years we have also evaluated fruit quality when the reflective materials were placed in the field early in the growth and development stages of fruit production. Laying down the mulch several months prior to harvest did not benefit the fruit quality or improve the color of apples or nectarines when compared to fruit from a field where mulch was installed 4 weeks prior to harvest. The mulch also became dirty fairly rapidly and its reflective properties were greatly diminished at the time it could have been of most use. I often hear or see reports of speakers saying we should be using red or white colored mulch rather than the metallic mulches for improving the color or quality of fruit. I suspect this idea came from the volumes of information on the effects red and far red light on crops such as tomatoes, soybeans, wheat, cowpea, potato, corn seedlings, watermelon, etc. There is also a great deal of information on color mulches used to control thrips, aphid, brown stink bug, etc. When investigating the use of both red and white plastic mulches, a great deal of time, money, and effort was spent to try to document the effects of these colored mulches in the production of fresh shipping apples and nectarines. Based on the literature and in talking with the various researchers about the specific wavelengths of light required to get a coloring response in the plant, a number of different red and white mulches were produced for our testing. A number of large scale field trials were developed using a variety of red and white mulches which had been produced to give us the best results expected, based on the field crop data in the literature. These products did give the fruit more color than the controls (white mulch was slightly better than red mulch), but in no one case did the color equal the color improvement produced by the silver mulch products. Fruit quality was not significantly improved either. There were no significant changes in degree brix (percent sugar), acid level, starch content, flesh firmness, or storage quality in any of the apple or nectarine fruit tested over the past two seasons (1995-1996). Some of these colored mulches were put into the field as long as three months prior to harvest, but did not significantly improve fruit color, size, or quality. |
