Ten herbicide treatments were evaluated for early season control of three broadleaf weeds and effects on marketable potato yields in low-organic, coarse-textured soil. All treatments controlled prostrate pigweed 100%. Trifluralin with metolachlor or with EPTC did not control kochia well. Pendimethalin alone or with EPTC controlled Russian thistle poorly, and produced the lowest marketable tuber yields. Fluorochloridone at 0.6 kg ai/ha caused chlorosis and reduced potato yield 11%. Treatments with metribuzin tended to have high potato yields.

Field experiments were conducted in 1990 and 1991 near Artesia and Las Cruces, NM to evaluate directed POST treatments of oxyfluorfen for the control of broadleaf weeds that emerge after thinning chile peppers. At Artesia, Wright groundcherry and prostrate pigweed reduced red pepper yield by 33% in untreated plots in 1990 and clusterflower reduced yield by 19% in 1991. At Las Cruces, Wright groundcherry, Palmer amaranth and common lambsquarters reduced yield by 61% in 1990 and by 76% in 1991. A sequential treatment of oxyfluorfen at 0.14 kg ai ha-1 2 wk after thinning, when the peppers were 15 cm tall, followed by 0.14 kg ha-1 4 wk after thinning controlled all species except common lambsquarters without injuring the peppers.

2,4-D diethanolamine control of kochia was influenced by the source of water used as the spray carrier. Sodium bicarbonate in one water source related to the reduced kochia control. Sodium bicarbonate in a water spray carrier antagonized 2,4-D control of all plant species evaluated. Antagonism increased with the tolerance of a species to 2,4-D, concentration of sodium bicarbonate, and spray volume. Sodium bicarbonate antagonism of 2,4-D phytotoxicity was greatest with low temperature and relative humidity.

Differential napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] tolerance by redroot pigweed (Amaranthus retroflexus L.) and prostrate pigweed (Amaranthus blitoides S. Wats.) was noted in field study. Redroot pigweed was readily controlled whereas prostrate pigweed was not. Germination studies in which both pigweed species were directly exposed to napropamide (0 to 25 ppm) indicated that prostrate pigweed was the most susceptible of the two species. Root growth rates of untreated prostrate pigweed were 30% greater than redroot pigweed. When seeds of both species were germinated in a 4-cm layer of napropamide in greenhouse study each species was controlled equally well. Exposure of germinating seedlings of the two pigweed species to napropamide 1 day before emergence resulted in differential control. Seedlings of redroot pigweed never developed beyond the cotyledon stage; whereas, prostrate pigweed seedlings were initially suppressed by the herbicide, but surviving plants continued to grow. An early preemergence application or mechanical incorporation of napropamide should enhance control of prostrate pigweed.

Winter sowing of lentil results in higher yields than a spring-sown crop. However, when lentil is winter-sown, the critical period of weed control is extended and might require sequential herbicide management strategies to obtain maximum yields. The efficacy of POST alone or soil applied followed by (fb) POST herbicides or hand weeding were evaluated in 2002 and 2003. Trifluralin (PPI) or pendimethalin (PRE) were applied at planting, and pyridate or oxyfluorfen were applied POST at the three- to four-leaf stage of lentil. The lowest level of weed biomass was recorded with all treatments, except pyridate alone in both years, pendimethalin PRE fb pyridate in 2002, and oxyfluorfen in 2003. Application of pyridate or oxyfluorfen POST alone resulted in lower yields. In 2002, trifluralin PPI or pendimethalin PRE fb one hand weeding or pendimethalin fb pyridate resulted in yields similar to the weed-free treatment. In 2003, yields were similar to the weed-free treatment, except pyridate or oxyfluorfen alone and trifluralin PPI fb oxyfluorfen. Weed species observed in the present study required sequential management to achieve both effective control and maximum lentil yield.