The effect of different levels of tillage and weed management on population, distribution, and germination of weed seed was evaluated in three tillage systems at Arlington and Hancock, WI, in 1989 and 1990. Over 60% of all weed seed in the top 19 cm of soil were found in the top 1 cm in no-tillage at both sites. As depth increased, concentration of weed seed declined logarithmically in no-tillage. In chisel plowing, over 30% of seed were in the top 1 cm and seed concentration decreased linearly with depth. Moldboard plowing had uniform distribution of weed seed in the top 19 cm of soil. Preemergence metolachlor plus atrazine decreased weed seed population by 50% compared with no treatment over all tillage systems. One year of the herbicide treatment plus handweeding to assure weed-free conditions did not reduce seed numbers in chisel plowing or moldboard plowing compared to herbicide alone. Seed numbers with no-tillage and weed-free conditions decreased by 40% relative to herbicide alone. Common lambsquarters germination was 40% greater in moldboard plowing and chisel plowing compared with no-tillage. Germination was highest in seed taken from 9 to 19 cm deep in moldboard plowing and from 0 to 9 cm deep in chisel plowing.

The effects of rye planting time, rye seeding rate, and rye/weed management systems on weed control and soybean yield were determined in field experiments near Arlington, WI from 1992 to 1994. Insufficient precipitation in 1992 resulted in limited soil moisture, less ground cover, less weed control, and lower soybean yields than in 1993 and 1994. The higher rye seeding rate provided more ground cover and better weed control than the lower rate in all years; however, it reduced soybean vigor. The optimum rye seeding rate was 112 kg/ha. The rye-only system reduced weed shoot biomass by 90, 82, and 60%, in 1992, 1993, and 1994, respectively, relative to the no-rye weedy check treatment. Killing rye 45 d after planting soybean gave optimum weed control. In 1993, rye alone suppressed the weeds without decreasing crop yield, but in 1994 crop yield was decreased due to inadequate weed control by rye. The results indicate that the rye living mulch technique can adequately control weeds without causing soybean yield reduction if weed pressure is low, ground cover and soil moisture are adequate and rye interference is minimal.

Concern about the effects of pesticides on the environment and the desire to reduce purchased inputs are stimuli to reduce herbicide use. Field research was conducted at two locations for two growing seasons to identify integrated weed management practices in corn that are effective and economical. Weed control treatments included PRE application of a herbicide mixture of 1.8 kg ai ha−1of atrazine plus 2.2 kg ai ha−1of metolachlor alone, this mixture broadcast or band-applied at a reduced rate in combination with mechanical weeding, and mechanical weeding alone. Weed control, corn yield, and economic returns were generally higher in treatments combining herbicides and mechanical weeding than those using only mechanical measures. Without herbicides, timeliness of rotary hoeing was critical. Herbicide use can be reduced 50 to 75% in integrated systems with minimal risk of yield loss due to uncontrolled weeds.

Many crop plants and perennial weed species have been known for their allelopathic effects. The question of whether annual weed species can be allelopathic remains unanswered. Consequently, studies were conducted in laboratory, greenhouse, and in the field to determine the allelopathic potential of weed and crop residues (above ground biomass) on corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. Water extracts of dried residues of common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), fall panicum (Panicum dichotomiflorum Michx.), giant foxtail (Setaria faberi Herrm.), green foxtail [Setaria viridis (L.) Beauv.], and yellow foxtail [Setaria glauca (L.) Beauv.] inhibited radicle elongation in corn; whereas, only common lambsquarters extract reduced coleoptile growth. Redroot pigweed, fall panicum, and green foxtail extracts inhibited hypocotyl elongation in soybeans. Residues of common ragweed (Ambrosia artemisifolia L.), velvetleaf (Abutilon theophrasti Medic.), and barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] as well as the above species inhibited corn and soybean growth in the greenhouse. Inhibition of the receiver species (corn and soybeans) was greater with the double‐pot watering method than subsurface and surface watering methods. Corn was inhibited most in silica sand, less in a silica sand and silt loam mixture (Typic Agriudoll fine, silty, mixed mesic), and least in silt loam soil under each method of watering. In the field, residues of barnyardgrass and giant foxtail reduced corn yield. Soybean yield reductions occurred ranging from 14 to 19% with common lambsquarters, redroot pigweed, velvetleaf, soybeans, and sunflower (Helianthus annuus L.) residues. Corn and giant foxtail residues enhanced soybean yield in the field. These results demonstrate the allelopathic potential of the residues and suggest that these residues may affect crop yields due to the inhibitory or stimulatory effects of allelochemicals present in the residues.

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