Ornamental tree growth with basin-applied herbicides.

Cider gum (Eucalyptus gunnii Hook. F.), Monterey pine (Pinus radiata D. Don), and camphor tree (Cinnamonium camphora (L.) J. Presl) were evaluated in a field study comparing the effects of herbicides on tree growth. Trees were planted on 13 May 1983 and treated on 20 May 1983, 10 Apr. 1984, and 4 Oct. 1984 with simazine, oryzalin, napropamide, and oxyfluorfen. Glyphosate was applied as a postemergence treatment in all basins on 20 Mar. 1984. None of the herbicides injured the trees. Trunk circumferencesin treated plots increased as much as 553% over untreated plots. All species showed a positive response to increasing weed control. Chemical names used: 6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine (simazine); 3,5-dinitro-N 4 ,N 4 -di- propylsulfanilamide (oryzalin); N,N-diethyl-2-(1-naphthalenyloxy)-propanamide (na- propamide); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxy- fluorfen); N-(phosphonomethyl)glycine (glyphosate). Appropriate staking, pruning, watering, and pest control practices are important con- siderations to ensure successful establish- ment and development of trees. One aspect of pest control that affects the early devel- opment of trees is weed management. Trees in landscape plantings in irrigated areas are planted either on the flat or with basins for irrigation. In some landscaped areas, weeds or turfgrasses are often allowed to grow to the base of the tree (Harris, 1969). Vegetation control may be attempted with a mechanical device or with preemergence herbicides (Nazer and Clark, 1984). Welker and Glenn (1985) demonstrated a positive response in trunk circumference and canopy of peach trees when grass was removed from the base of the tree. Eucalyptus planted with- out basins grew more when turf was re- moved (Harris, 1969). Glyphosate has been used without phytotoxicity to young honey- locust trees (Prochaska and Fretz, 1976). If preemergence herbicides could be used in the planting basins without injury to the young trees, improved growth and tree vigor might be obtained. Since we found no stud- ies where preemergence herbicides were used on young trees in planting basins, we deter- mined the effects of four preemergence her- bicides on three ornamental tree species when applied in the planting basin. Monterey pine (4-liter container), cider gum (9-liter container), and camphor tree (5 × 5 cm liners) were planted at the Univ. of Cal- 1.0d 1.0d 1.2e 1.0d z A rating scale was used with 1 = no control and 10 = complete control. y Mean separation in columns by Duncan's multi- ple range test, P = 0.05. x