Commercial Adaptations of Mechanical Stimulation for the Control of Transplant Growth

The commercial use of mechanical stimulation to control transplant growth is quite limited. To be commercially successful, the technique must be simple and flexible, and must not reduce plant quality. Brushing was applied to tomato (Lycopersicon esculentum) seedlings growing at a density of 2100 plants mby daily stroking with a piece of polystyrene. Ten or twenty daily strokes typically provided significant height control without plant damage. Increasing the interval between strokes to up to 10 minutes resulted in the same amount of height control as continuous brushing. There were typically no differences between treating the plants at 0800 or at 1700 hours. Significant height control was achieved if treatments were begun at the first or second true leaf stage, but treatments begun at a later stage of development resulted in leaf damage. Brushing before transplanting to the field resulted in a significant decrease in stem elongation (-20%). However, there were no significant differences between brushed and unbrushed plants in long-term growth or final fruit yield after transplanting to the field. Preliminary studies were also conducted on four bedding plant species: geranium (Pelargonium x hortorum), impatiens (Impatiens holstii), petunia (Petunia hybrida) and pansy (Viola tricolor). Brushing was applied to seedlings growing at a density of 1500 plants musing either polythene or plastic netting. For geranium and impatiens, any reductions in plant stature were associated with significant plant damage. Brushing induced a prostrate growth habit and leaf distortion in petunia and significantly reduced leaf area and shoot dry weight. Pansy plants were undamaged by 10 or 20 brush strokes per day and showed a significant (17-22%) decrease in petiole length, typically without significant effects on leaf area, dry weight or days to flower. Brushing provides a flexible, effective method for controlling tomato and pansy transplant size without adversely affecting quality or long-term growth.