Pepper yield is significantly impacted by weed competition. The broadleaf weeds redroot pigweed (Amaranthus retroflexus) and hairy galinsoga (Galinsoga ciliata) have reduced pepper yield by as much as 88% and 99%, respectively (Fu and Ashley, 2006). Purple nutsedge (Cyperus rotundus) has reduced pepper yield by as much as 70% (Morales-Payan et al., 2003). Weeds must be controlled at least through the first half of the cropping season to avoid significant yield loss in pepper, and this level of weed control may not always be achieved with the use of herbicides applied before weed emergence (Amador-Ramirez, 2002). However, the majority of the herbicides available for weed control in pepper are only selective to pepper when applied as preplant (PP), preplant incorporated (PPI), or pre-emergence (PRE) applications applied before weed emergence. In fact, the only herbicides registered for postemergence (POST) over-the-top weed control in pepper are gramincides that control only grass weeds (Orzolek et al., 1986; Stall, 2007).
Clomazone provides control of certain annual grasses and several broadleaf weeds, including common ragweed (Ambrosia artemisiifolia), common lambsquarters (Chenopodium album), prickly sida (Sida spinosa), velvetleaf (Abutilon theophrasti), and jimsonweed (Datura stramonium) in pepper (Ackley et al., 1992; Stall, 2007). Pepper tolerance to PRE clomazone applications is due to lower uptake and more rapid metabolism of clomazone to inactive metabolites in pepper compared with other more sensitive crops and weeds (Weston and Barrett, 1989). Clomazone tolerance is greatest when applied PP, PPI, or POST to transplanted pepper than when applied PRE to direct-seeded pepper (Ackley et al., 1998; Cavero et al., 1996). On the Coastal Plain soils of eastern Virginia, clomazone is often applied PP or PPI in combinations with napropamide, metolachlor, or trifluralin to improve suppression of the broadleaf weeds smooth pigweed (Amaranthus hybridus), carpetweed, and several annual grasses (Ackley et al., 1992). Metolachlor can also be applied with clomazone to improve control of yellow nutsedge (Cyperus esculentus) (Stall, 2007; Vencill, 2002). However, full-season control of all broadleaf and sedge weeds is unlikely with these clomazone programs.
Selected herbicides have been evaluated for POST over-the-top weed control in pepper. The photosystem II (PSII) inhibitor bentazon was evaluated for POST weed control in several varieties of peppers because it is currently used to control several broadleaf weeds and yellow nutsedge in minor crops like mint (Mentha spp.), pea (Pisum sativum), and bean (Phaseolus spp.) (Baltazar et al., 1984). However, pepper injury and yield varied greatly between pepper varieties treated with different POST rates of bentazon (Baltazar et al., 1984; Wolff et al., 1989). This variability in tolerance was due to differential detoxification of bentazon among these pepper varieties (Baltazar and Monaco, 1984). Another PSII inhibitor, metribuzin, was also evaluated as a POST treatment for weed control in pepper based on its safety in tomato (Solanum lycopersicum) and potato (Solanum tuberosum). However, metribuzin caused severe injury and yield reductions when applied POST in pepper (Orzolek et al., 1986). Similarly, the ALS-inhibiting herbicide rimsulfuron was evaluated, but the level of tolerance was not commercially acceptable (Ackley et al., 1998; Stall, 1999). Another ALS inhibitor, halosulfuron, has provided reduced phytotoxicity on pepper when compared with rimsulfuron (Stall 1999).
The objective of this research was to determine if POST applications of several ALS-inhibiting herbicides would provide selective broadleaf weed control in transplanted bell peppers. An additional objective was to characterize pepper tolerance to these ALS inhibitors with visual injury evaluations and measurements of pepper height, biomass, chlorophyll content, and yield.
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