In an effort to dwarf seed orchard trees without reducing fruitfulness, nine growth-retardant chemicals were applied at several concentrations each as either aqueous foliar sprays or oil-based bark bands. All treatments which significantly retarded growth also caused injury or death. Mefluidide, as a 0.7% foliage spray, reduced growth and caused only minimal injury. Effects of the chemicals on seed production could not be observed, as no control or treated trees flowered. Slash pine was more sensitive to the chemicals than loblolly pine.
Seed-orchard operations would benefit if trees could be kept short without sacrificing seed yield on a given area. To test the feasibility of chemical dwarfing, five growth-retarding chemicals were applied to foliage or bark of 2-year-old loblolly (Pinustaeda L.) and slash (P. elliottii Engelm. var. elliottii) pines in February. The most effective chemical for reducing height growth without toxicity was EL-500 (α-(l-methylethyl)-α-(4-(trifluoromethoxy)phenyl)-5-pyrimidinemethanol), a compound related to ancymidol (α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol). It reduced 1-year growth to about half that of the controls in both species when applied as an aqueous foliar spray or an oil-based bark band. Although the dwarfed growth appeared otherwise normal, the possible effects of EL-500 on future flowering and seed yield have yet to be determined.
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