Herbicides for Container-grown Rain Forest Species

Abstract

Four granular formulations of preemergence herbicides-oxadiazon, oxadiazon in combination with simazine, dichlobenil, and oxyfluorfen + oryzalin-were evaluated for weed control and phytotoxic effects on 10 species of container-grown Australian rain forest plants. Herbicides were applied at half and at one and two times the manufacturer's recommended rate. Oxyfluorfen + oryzalin, oxadiazon, and oxadiazon + simazine controlled all weed species at half the recommended rates (1.0 + 0.5, 2.0, and 2.0 + 0.5 kg·ha-1, respectively) with no phytotoxic effects after 10 weeks to nine of the 10 rain forest species tested: broad-leafed lilly-pilly [Acmena hemilampra (F. Muell. ex Bailey) Merr. and Perry], red ash [Alphitonia excelsa (Cunn. ex Fenzl) Reisseck ex Benth.], rusty bean [Dysoxylum rufum (A. Rich.) Benth.], macaranga [Macaranga tanarius (L.) Muell. Arg.], fibrous satinash [Syzygium fibrosum (Bailey) T. Hartley and Perry], Queensland golden myrtle [Metrosideros queenslandica L.S. Smith], cluster fig [Ficus racemosa L.], corduroy tamarind [Arytera lautereriana (Bailey) Radlk.], and celerywood [Polyscias elegans (F. Muell and C. Moore) Harms]. Dichlobenil depressed plant growth of red ash and failed to control bittercress (Cardamine hirsuta L.) and green amaranth (Amaranthus viridus L.), even at twice the recommended rate (4.0 kg·ha-1). All herbicides applied at half the recommended rates produced minor to moderate plant injury within 5 weeks of the first application to corduroy tamarind and northern silky oak [Cardwellia sublimis F. Muell.]. A second application 10 weeks after the first caused no significant plant injury to corduroy tamarind but resulted in severe plant injury to northern silky oak. This finding validates the previously reported sensitivity of Proteaceous spp. to preemergence herbicides. Chemical names used: (2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4 oxadiazoline-5-one) (oxadiazon); (2-chloro-4,6-bisethylamino-1,3,5-triazine) (simazine); 2,6-dichlorobenzonitrile (dichlobenil); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); and 3,5-dinitro-N4,N4 -dipropylsulfanilamide (oryzalin).