Large weeds, particularly amaranths, are a serious impediment to mechanical harvesting of jalapeno peppers. Several herbicides were applied in 1998 and 1999 postemergence topical (PT) to commercial fields when peppers had four to six leaves, or postdirected (PD) with a shielded sprayer ≈1 month later, and evaluated for crop injury, weed control, and effects on yield. Treatments were applied to four-row plots 9 m long with a CO<subscript>2 backpack sprayer. PT treatments included pyrithiobac sodium at 0.036, 0.053, or 0.071 kg·ha–1 a.i. with nonionic surfactant or crop oil concentrate, metolachlor at 1.68 kg·ha–1 a.i., and oxyfluorfen at 0.14 or 0.28 kg·ha–1 a.i.. PD treatments consisted of the same rates of pyrithiobac sodium with nonionic surfactant only, and the same rates of oxyfluorfen. Pyrithiobac sodium PT caused significant chlorosis (reduction in SPAD chlorophyll) in new foliage and reduction in plant height after 1 week, but plants recovered with no effect on final plant height, chlorophyll, or yield. No significant difference was observed between the two adjuvants. Metolachlor had no measurable effect on pepper growth or yield. Oxyfluorfen PT killed young apical tissue and caused chlorosis of immature leaves. Plants recovered, but plant height was reduced by 14% to 28% and yield by 11% to 43%. PD treatments had no effect on pepper growth or yield. All herbicides provided adequate weed control under light pressure. Pyrithiobac sodium appears to have potential as a postemergence herbicide for control of amaranth in jalapeno peppers.
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