Current Concerns with Photoselective Films
One draw back of the photoselective films that we tested is their short film life. We have evaluated the film life under both protected (in a greenhouse) and unprotected (exposed to full sun) conditions at Clemson University and at a nursery research site (Carolina Nursery, Monks Corner, SC). Films tested in the greenhouse lasted longer (over one year) than those films tested under natural conditions. The dye in the films tested under unprotected conditions began to degrade during the first year of exposure (10 to 12 months). Short film life is a limitation to the commercial applications of the photoselective films we tested but experiments are being conducted to increase the stability of the dyes in the films under natural environments. Using the photoselective film as the inner layer of a double layered poly house may help extend the life of the films. Experiments are currently underway to test the film in this type of situations.
Another concern of using photoselective films is that the reduction of light transmission may limit their use in low light seasons and in the northern latitudes where sunlight is limited. In a given day, the red:far-red ratio of sunlight is relatively constant (about 1.1) from sunrise to sunset; however, during a half-hour-period before sunrise or after sunset, red:far-red ratio is reduced due to the increase in far-red light. Therefore, exposing plants to far-red light absorbing photoselective films at the end of the day may help effectively exclude far-red light in the evening while maximizing the light during the daytime. We are currently testing the use of photoselective films as an end of the day curtain to block far-red light during the evening hours. Preliminary experiments were conducted with cucumber by exposing seedlings continuously to far-red light absorbing films or by exposing seedlings to films at the end of the day (from 3:00 PM to 9:00 AM or from 5:00 PM to 9:00 AM, in October to November). Treatments were terminated after 15 days. The shortest plants were those grown continuously in far-red light absorbing (YXE-10) chambers (
Figure 3: Effect of end-of-day exposure of YXE-10 film on cucumber seedlings “plant figure” ). End of the day exposure to YXE-10 film was also effective in height reduction. However, the height reduction by end of the day exposure (25% height reduction) was not as high as continuous exposure (44% height reduction). There was no difference in height between the two end of the day exposure treatments to YXE-10 film, indicating that later exposure to film was as effective.
Plants grown continuously in YXE-10 chambers had the lowest shoot dry weight. Dry weight of end of the day exposed plants was greater than continuous YXE-10 plants, suggesting that end of the day exposure can minimize the dry weight reduction. By using photoselective film as an end of the day curtain, film life may also be extended. Although effective with cucumbers, to make this strategy commercially useful, a wide range of crops must be tested. If effective with a range of crops, this will provide an opportunity to maximize the use of sunlight during the daytime and achieve a reasonable height reduction without using chemicals.
As the general public becomes more concerned with the chemical use, interest in using non-chemical alternatives to regulate plant growth and to control pests and diseases will increase. With the commercial development of photoselective greenhouse covers or shade material in the near future, nursery and greenhouse industry could reduce costs for growth regulating chemicals, reduce health risks to their workers and consumers, and reduce potential environmental pollution.