Abstract

Efficacy of Cutless (flurprimidol), Sumagic (uniconazole), and Atrimmec (dikegulac) as affected by application date after pruning was investigated with Pyracantha × ‘Teton’, Ligustrum × vicaryi, and Euonymus fortunei var. coloratus. Cutless (flurprimidol) applied to the medium surface, or foliar sprays of Sumagic (uniconazole) or Atrimmec (dikegulac) were applied 1, 2, 3 or 7 days after pruning (DAP) and to unpruned plants in spring 1989. Height and width were recorded weekly into November, 1989. The effect of these plant growth regulators (PGRs) on short-term plant water relations was measured at 2, 3, 18, 22, or 24 days on unpruned plants and plants treated 2 DAP. Growth rate of Pyracantha was reduced for 6 to 7 weeks if Sumagic (uniconazole) was applied 2 DAP or less, or to unpruned plants; otherwise growth rate was reduced 4 to 5 weeks. Sumagic (uniconazole) reduced Pyracantha growth rate more than Atrimmec (dikegulac); however, Atrimmec-treated plants had a more normal growth habit by the end of the experiment. Atrimmec (dikegulac) also suppressed Ligustrum growth without detrimentally affecting plant appearance. Cutless (flurprimidol) was the only PGR that effectively inhibited growth of Euonymus; however, this treatment excessively dwarfed Pyracantha and Ligustrum. The influence of Atrimmec (dikegulac) and Cutless (flurprimidol) on leaf area varied with the species, and pruning had no effect. Short-ternl effects of Sumagic (uniconazole), Cutless (flurprimidol), and Atrimmec (dikegulac) on transpiration and stomatal conductance to water vapor were species dependent, with some species exhibiting partial stomatal closure. Improvement of plant water status (stem water potential and relative leaf water content) occurred in some cases.