Since 1990 Dr. Peg McMahon has been working on developing a non-chemical method of retarding plant stem elongation, commonly called ‘stretch’. Stretch is a problem in greenhouse production as tall, spindly plants have low commercial value.
Dr. McMahon is investigating the possibility of changing the quality of light received by plants to regulate the way they grow. Plants in full sun and not crowded by other plants are compact and bushy, qualities deserved for many floral potted crops. There is a specific region of the solar light spectrum, far-red (FR), that signals to the plant when light levels decrease or the plant is crowded by other plants. By removing FR, Dr. McMahon has demonstrated that plants continue to grow as if in full sun even when crowded on a greenhouse bench. Specifically, stem elongation is reduced and leaves are smaller and darker green (compared to plants grown in unfiltered light at the same intensity) which also enhances the appearance of the plant.
Dr. McMahon’s research method has been to use a solution of copper sulfate or bluestone in the channels of doubled-walled polycarbonate or acrylic panels. Copper sulfate very effectively absorbs FR. However, other than as a research tool, the technique has limitations in its use commercially. Installation of the system would be expensive. Copper sulfate is phytotoxic so any leaks or spills could cause serious damage to plants.
An alternative is to incorporate FR absorbing characteristics in a plastic film that could be used either as a covering for greenhouses or as part of an internal shading system. One system or the other could be easily installed in most existing structures. Until recently, FR absorbing plastic films were not available. However, last year Dr. McMahon located and established a collaborative research effort with a Japanese chemical company, Mitsui Chemicals, Inc. that has developed FR absorbing films. Recently, Dr. McMahon received a 3 year grant from the company to work with them to bring the technology to the grower. The grant enables her to study the plastics on a large scale in a greenhouse. She is working with chemists in the company to improve the FR absorbing characteristics of the film and to improve its longevity. Dr. McMahon sees this technology as soon becoming a commonplace tool for plant growth regulation in the greenhouse.
