Controlling weed contamination in nursery stock is difficult in ornamental production. Although cultural practices for weed control in nurseries include mulching and the use of fabrics to impede the development of emerging weeds, these techniques are not completely effective in the absence of a chemical control (Case et al., 2005; Mathers and Ozkan, 2001). Acetyl-CoA carboxylase inhibitors are effective at remedially managing grasses in dicotyledonous nursery stock (Senesac, 2002); however, selective control of broadleaf weeds in ornamental systems is more difficult. In part, challenges derive in that both broadleaf weeds and many desirable ornamentals are both dicotyledonous species with variable sensitivity to postemergence herbicides (Case et al., 2005; Derr, 1994).
To date, there are few POST herbicides registered for selective broadleaf control in ornamental plants. These herbicides do not provide broad-spectrum broadleaf weed control in ornamental production and/or are not registered for use over the top of many ornamental species.
Mesotrione, topramezone, and tembotrione are herbicides that inhibit the HPPD enzyme. These herbicides impede the production of plastoquinone in susceptible species, ultimately preventing the production of photoprotective carotenoid compounds. As a result, the plant’s ability to sequester singlet- and triplet-state oxygen and dissipate excess photosynthetic active radiation is compromised (Niyogi, 1999). Eventually foliar plant tissue becomes bleached, necrotic, and photosynthetically inactive resulting in plant death. Mesotrione, topramezone, and tembotrione are labeled for weed control in corn (Zea mays) and multiple turfgrass species (Elmore et al., 2011; Gettys and Haller, 2009). Weeds controlled by these herbicides include (but are not limited to) common cocklebur (Xanthium strumarium), common lambsquarters (Chenopodium album), smartweed species (Polygonum sp.), common ragweed (Ambrosia artemisiifolia), yellow nutsedge, nimblewill (Muhlenbergia schreberi), and crabgrass (Digitaria sp.) (Beam et al., 2006; Giese et al., 2005; Jones and Christians, 2007; Senseman, 2007; Willis et al., 2006).
Several researchers have reported moderate injury (<45%) to burning bush, vinca (Vinca sp.), and loblolly pine (Pinus taeda) with mesotrione applications (Jackson et al., 2009; Little et al., 2004; Senesac and Tsontakis-Bradley, 2007). Other researchers (Vea and Palmer, 2010) showed that mesotrione applications caused unacceptable phytotoxicity to over 20 ornamental plant species. However, data describing ornamental tolerance to topramezone and tembotrione are minimal. Thus, our objective was to determine ornamental tolerance and weed control efficacy with applications of the HPPD-inhibiting herbicides mesotrione, tembotrione, and topramezone compared with bentazon, an important ornamental herbicide on common ornamental plant and weed species in Tennessee.
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