In northern U.S. vegetable cropping systems, attempts at no-till (NT) production have generally failed because of poor crop establishment and delayed crop maturity. Strip tillage (ST) minimizes these problems by targeting tillage to the zone where crops are planted while maintaining untilled zones between crop rows, which foster improvements in soil quality. ST has been shown to maintain crop yields while reducing energy use and protecting soils in vegetable crops, including sweet corn, winter squash, snap bean, carrot, and cole crops. Despite potential benefits of ST, weed management remains an important obstacle to widespread adoption. Increased adoption of ST in cropping systems for which effective, low-cost herbicides are either limited (e.g., most vegetable crops) or prohibited (e.g., organic systems) will require integration of multiple cultural, biological, and mechanical approaches targeting weak points in weed life cycles. Weed population dynamics under ST are more complex than under either full-width, conventional tillage (CT) or NT because weed propagules—as well as factors influencing them—can move readily between zones. For example, the untilled zone in ST may provide a refuge for seed predators or a source of slowly mineralized nitrogen, which affects weed seed mortality and germination in the tilled zone. Greater understanding of such interzonal interactions may suggest manipulations to selectively suppress weeds while promoting crop growth in ST systems. Previous studies and recent experiences in ST vegetable cropping systems suggest a need to develop weed management strategies that target distinct zones while balancing crop and soil management tradeoffs. For example, in untilled zones, optimal management may consist of weed-suppressive cover crop mulching, combined with nitrogen exclusion and high-residue cultivation as needed. In contrast, weed management in the tilled zone may benefit from innovations in precision cultivation and flame-weeding technologies. These short-term strategies will benefit from longer-term approaches, including tillage-rotation, crop rotation, and cover cropping strategies, aimed at preventing seed production, promoting seed predation and decay, and preventing buildup of problematic perennial weeds. However, a concerted research effort focused on understanding weed populations as well as testing and refining integrated weed management strategies will be necessary before ST is likely to be widely adopted in vegetable cropping systems without increased reliance on herbicides.

The effect of planting system and cover crop residues on weed emergence in irrigated vegetable row crops was studied in field experiments from 1995 through 1997. Vegetable crops were either no-till planted (NTP) through cover crop residues or conventionally planted (CP) into soil with cover crop residues incorporated. NTP reduced emergence of hairy nightshade by 77 to 99% and Powell amaranth emergence by 50 to 87% compared with CP. Cover crop treatments were much less important than planting system in regulating weed emergence. Tillage in the spring did not increase the number of viable seeds near the soil surface. Hairy nightshade emergence ranged from 0.6 to 9.8% of the intact seeds in CP compared with 0 to 0.1% emergence of the seeds in the NTP plots. Powell amaranth emergence ranged from 4.9 to 6.5% of the intact seeds in CP contrasted with only 0.4 to 0.9% emergence of the seeds in NTP plots.

Field experiments were conducted on a silty clay loam in Corvallis, OR during the summers of 1995 and 1996 to study the effects of soil solarization, spring-planted green manure crops, fumigation with metham, and combinations of these treatments on annual bluegrass seed survival. Annual bluegrass seeds were incorporated into the soil as a bioassay species and soil samples extracted to a depth of 15 cm to determine effects on seed survival. Soil solarization was applied over a 53- or 59-d period using a 0.6-mil clear polyethylene film. Soil samples were collected from four depths after the solarization period in both solarized and nonsolarized plots and surviving seeds germinated in a greenhouse. Maximum soil temperatures recorded at 5-, 10-, and 20-cm depths were 52, 47, and 33 C in solarized soil, respectively. Solarization reduced annual bluegrass seed survival from 89 to 100% in the upper 5 cm of soil, but did not reduce survival below 5 cm. Solarization may have enhanced seed survival below 5 cm. Cover crops of barley, rapeseed, and sudangrass generally increased survival of annual bluegrass seeds buried 2.5 to 15 cm deep in the soil. Green manure cover crops plus solarization did not improve the efficacy of solarization alone and in some cases diminished the effectiveness of solarization. Solarization significantly improved the efficacy of one-quarter rates of metham (230 L/ha) in the top 5 cm of soil, reducing overall annual bluegrass seed survival in the soil by 40% compared with metham alone (230 L/ha) but only 30% compared with solarization alone. The conventional rate of metham (930 L/ha) was the most effective and consistent treatment across all depths.

No abstract

Manufacturers of several POST corn herbicides recommend tank-mixing their herbicides with atrazine to improve performance; however, future regulatory changes may place greater restrictions on atrazine use and limit its availability to growers. Our research objectives were to quantify the effects of tank-mixing atrazine with tembotrione compared to tembotrione alone on (1) weed control, (2) variability in weed control, and (3) sweet corn yield components and yield variability. Field studies were conducted for 2 yr each in Illinois, Oregon, Washington, and Ontario, Canada. Tembotrione at 31 g ha−1 was applied alone and with atrazine at 370 g ha−1 POST at the four- to five-collar stage of corn. The predominant weed species observed in the experiment were common to corn production, including large crabgrass, wild-proso millet, common lambsquarters, and velvetleaf. For nearly every weed species and species group, the addition of atrazine improved tembotrione performance by increasing mean levels of weed control 3 to 45% at 2 wk after treatment. Adding atrazine reduced variation (i.e., standard deviation) in control of the weed community by 45%. Sweet corn ear number and ear mass were 9 and 13% higher, respectively, and less variable when atrazine was applied with tembotrione, compared to tembotrione alone. Additional restrictions or the complete loss of atrazine for use in corn will necessitate major changes in sweet corn weed management systems.