A new technology for controlling plant height is being investigated at The Ohio State University. Dr. Peg McMahon is studying the use of plastic films that selectively filter out the portion of the light spectrum associated with stem elongation (stretch). These films, available for use in research little more than a year, should become available for use in the commercial greenhouse soon.
The idea for the films comes from the use of another filtering technique, the use of liquid copper sulfate (bluestone) as a light absorbing material. Copper sulfate is very effective absorber of far-red radiation which provides the signal the plant receives when crowding has occurred. By removing far- red from the light received by the plant, the plant is "tricked" into reacting as if it is not crowded. As a result, plant growth is compact and bushy. The resulting growth resembles that of plants which have received an effective treatment of a chemical growth retardant. The idea of "tricking" the plant into doing something is not new. It is the premise that allows the use of black cloth shading to produce mums year-round.
The use of copper sulfate as a filter was not practical in a greenhouse situation. The technology involved sealing the liquid within double-walled polycarbonate or acrylic panels, having a pumping and storage system, and dealing with a phytotoxic and corrosive material. The films provide a more practical means of utilizing the technique.
The plastic films can be used as polyhouse coverings or as internal shading systems. Either way, the retrofitting of an existing structure would be relatively inexpensive. The filters would not replace any existing plant growth retarding strategies, e.g. lowering temperatures, reducing water availability, - DIF, chemical growth retardants. Instead, these plastics would provide an additional tool. Currently, we are investigating the overall effectiveness of the films, the proper time of day to utilize the films, what techniques can be used to override the effects of the films. The latter would be important in cases where the films are used as semi-permanent coverings. We are also investigating how the films interact with other plant processes such as flowering.
