A 2-year study evaluated the effects of three weed species: eclipta [Eclipta alba (L.) Hasskarl], prostrate spurge (Euphorbia supina Raf.), and wood sorrel (Oxalis stricta L.) on growth of container-grown `Gumpo White Sport' azalea (Rhododendron eriocarpum), R. x `Fashion', and Berberis thunbergii DC. var. atropurpurea `Crimson Pigmy'. Competitiveness among weed species as ranked from greatest to least was eclipta, prostrate spurge, and wood sorrel. Greater populations of eclipta and prostrate spurge resulted in decreased shoot dry weight of `Fashion' and `Gumpo White Sport' azalea. Prostrate spurge had a similar effect on `Crimson Pigmy' barberry in both small (3.8-liter) and large (15.2-liter) containers, while eclipta reduced shoot dry weight of barberry only in large containers. Wood sorrel had little effect on shoot dry weight of `Fashion' and `Gumpo White Sport' azalea.

Preemergence herbicides were evaluated for control of yerba-de-tago [Eclipta alba (L.) Hasskarl] and for phytotoxicity to four container-grown landscape species. Herbicides providing excellent control (less than one weed/pot) were chlorimuron at 0.035 and 0.07 kg·ha-1, chlorimuron + metribuzin at 0.075 + 0.485 kg·ha-1, and oryzalin at 4.5 and 9.0 kg·ha-1. Injury within 30 days after treatment occurred with applications of oxyfluorfen, lactofen, and fomesafen at the × 1 and × 2 rates on Ilex vomitoria Ait. ‘Nana’ (dwarf yaupon), Rhododendron satsuki ‘Pink Gumpo’ (‘Pink Gumpo’ azalea), R. obtusum (Lindl.) Planch. ‘Coral Bells’ (‘Coral Bells’ azalea), and Liriope muscari L. ‘Big Blue’ (lily turf). Injury symptoms were not present after 60 days, except with applications of lactofen at 0.44 kg·ha-1 and fomesafen at 1.1 kg·ha-1. All other herbicides were safe on the four ornamental species. Chemical names used: 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide (metolachlor); N,N-diethyl-2-(l-naphthaIenyloxy)propanamide (napropamide); 3-[2,4-dich-loro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); N-(l-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); 6-chloro-N,N-diethyl-1,3,5-triazine-2,4-diamine (simazine); 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin); methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate (bifenox); 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide (alachlor); 2-[[[[4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid (chlorimuron); 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin); (±)-2-ethoxy-l-methyl-2-oxoethyl 5-[2-chloro-4-(trifluoromethyl)phenoxyl]-2-nitrobenzoate (lactofen); and 5-[2-chloro-4-(trifluoromethyl)phenoxyl]-N-(methysulfonyl)-2-nitrobenzamide (fomesafen).