Tree Growth Retardation by Injection of Chemicals
Subhash C. Domir and Bruce R. Roberts
Abstract: A long term study was conducted to evaluate growth retardation capabilities of potential plant growth regulators for landscape trees. These investigations were carried out in the greenhouse and at several geographic field locations with different climatic conditions. A portable, airpowered equipment system was used for injecting field trees with low volumes of highly concentrated aqueous growth regulator solutions. One- to two-year-old seedlings of approximately 25 species were tested under greenhouse conditions. Twelve chemicals were screened as potential growth retardants. The most consistently effective chemicals tested over a wide range of tree species were maleic hydrazide, dikegulacsodium, and DOWCO 391. At appropriate concentrations, these chemicals controlled sprout regrowth in most species without unacceptable phytotoxicity. Using the pressure injection technique, maleic hydrazide and dikegulac were tested for their control effectiveness on 14 species in 12 states and 17 cities. Both chemicals were successful in controlling growth of almost all species for one year. In several instances regrowth was controlled for two growing seasons following treatment. Generally, dikegulac was more consistent than maleic hydrazide in generating a growth retardation response. Field studies show that significant regrowth variability exists among trees treated with a given dosage of chemical. This variability may be attributed to environmental and/or plant factors. In order to obtain similar growth control effects for identical species located at various geographical locations, different concentrations of the same chemical may be needed.