The effects of preemergence herbicides on root and shoot growth of redtip photinia (Photinia × fraseri Lindl.), abelia (Abelia× grandiflora × A. Schumannii Rehd.), azalea (Rhododendron obtusum Planch. ‘Tradition’) and Japanese holly (Ilex crenata Thunb.‘Helleri’) were evaluated in container studies. Experimental design was a randomized complete block with four replications and five containers of each species per plot. Root and shoot weights were recorded five weeks after either one, two or three herbicide applications. Ronstar (oxadiazon) and Ornamental Herbicide II [OH2 (oxyfluorfen plus pendimethalin)] had essentially no adverse effect on shoot or root development of the four species. Rout (oxyfluorfen plus oryzalin), Surflan (oryzalin), Gallery (isoxaben), and Factor (prodiamine) decreased root and/or shoot development of certain species, especially at the first two harvests. Plant size at treatment may be a factor in the extent of stunting caused by preemergence herbicides, with larger plants being more tolerant. Stunting of shoot and root growth appeared to be temporary.
2Associate Professor and Graduate Research Assistant. Senior author is currently a visiting scientist, Rutgers University, Department of Plant Science, P.O. Box 231. New Brunswick, NJ 08903-0231.