A reduced-till (RT) experiment determined the effect of rye seeding density and method of kill on rye biomass persistence, weed suppression, and tomato yield. ‘Wheeler’ rye was seeded at 56, 110, and 170 kg ha−1in the fall of 1988 and 1989 in Champaign, IL; Lexington, KY; and Lafayette, IN. One wk before transplanting tomatoes, rye was desiccated either by applying glyphosate at 1.1 kg ha−1and mowing (RT-glyphosate) or by mowing alone (RT-mowed). Both methods left rye residues on the soil surface as a mulch. Seeding density did not affect rye biomass, weed control, or tomato yield. Rye biomass differed depending on location and year, ranging from 320 to 1150 gm−2. Rye was completely killed by glyphosate, but regrew following mowing. RT-glyphosate suppressed weeds for 4 to 8 wk, which was similar to the suppression from conventional tillage (fall plowing with spring disking and harrowing) with trifluralin and metribuzin (CT-herbicide). Weed communities varied, but redroot pigweed and giant foxtail were present at all three locations. All treatments required supplemental weed management for commercially acceptable control. Except for IL in 1990, processing tomato yields (kg ha−1) in RT-glyphosate with hand-weeding were equal or better than yields in the CT treatments.

Studies were conducted to evaluate biomass production, tissue phytotoxicity, and allelochemical content of rye (Secale cereale L.) shoots grown in three fertility regimes (low, medium or high) in the greenhouse. Wheeler rye or a polyculture of rye and hairy vetch (Vicia villosa Roth) grown with high fertility produced the greatest biomass (78.7 and 82.7 g), with the lowest root-to-shoot ratio (0.22 and 0.43) produced in the high-fertility treatments. The polyculture treatment grown with low fertility had a greater proportion of hairy vetch (18%) than when grown with high fertility (6%). Rye shoot residue phototoxicity was affected by fertility regime. Radicle elongation of cress (Lepidium sativum L.) and barnyardgrass [Enchinochloa crus-galli (L.) Beauv. I was inhibited by rye shoot residues in a modified Parker bioassay. Rye shoot residue grown with low fertility was less inhibitory to cress radicle elongation than rye residue from the medium- or high-fertility regimes. Extracts of dried rye shoots grown with high fertility were less inhibitory than extracts from other fertility regimes. The concentrations of ether extracts of rye causing 50% inhibition (I50) of cress radicle elongation were between 125 and 276 µg/ml for greenhouse-grown and 60 and 138 µg/ml for the field-grown rye shoots. The major phytotoxic compounds in the rye shoot extracts were identified as DIBOA and BOA. The concentration of DIBOA in the greenhouse-grown rye shoots ranged between 128 and 423 µg/g while BOA concentration ranged between 2.5 and 31 µg/g. DIBOA and BOA levels were lowest in rye shoots grown with high fertility. Correlations between rye shoot biomass, DIBOA and BOA concentration, and cress barnyardgrass radicle length were significant.

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Organic agricultural systems increase the complexity of weed management, leading organic farmers to cite weeds as one of the greatest barriers to organic production. Integrated Weed Management (IWM) systems have been developed to address the ecological implications of weeds and weed management in cropping systems, but adoption is minimal. Organic agriculture offers a favorable context for application of IWM, as both approaches are motivated by concern for environmental quality and agricultural sustainability. However, adoption of IWM on organic farms is poorly understood due to limited data on weed management practices used, absence of an IWM adoption metric, and insufficient consideration given to the unique farming contexts within which weed management decisions are made. Therefore, this study aimed to (1) characterize organic weed management systems; (2) identify motivations for, and barriers to, selection of weed management practices; and (3) generate guiding principles for effective targeting of weed management outreach. We surveyed Midwestern organic growers to determine how specified psychosocial, demographic, and farm structure factors influence selection of weed management practices. Cluster analysis of the data detected three disparate, yet scaled, approaches to organic weed management. Clusters were distinguished by perspective regarding weeds and the number of weed management practices used. Categorization of individual farms within the identified approaches was influenced by primary farm products as well as farmer education, years farming, and information-seeking behavior. The proposed conceptual model allows weed management educators to target outreach for enhanced compatibility of farming contexts and weed management technologies.

Field and greenhouse studies were conducted to evaluate herbicides in pumpkin. Field experiments at three Illinois locations determined weed control and crop injury from clomazone, dimethenamid, ethalfluralin, sulfentrazone, imazamox, RPA 201772, flumiclorac, and halosulfuron applied preemergence. Clomazone plus sulfentrazone controlled redroot pigweed 78 to 99%, ivyleaf morningglory 80 to 97%, common lambsquarters 97%, common purslane 84 to 99%, and velvetleaf 55 to 99%. Imazamox plus clomazone commonly provided more consistent broadleaf weed control than did ethalfluralin plus clomazone. RPA 201772 when used on sandy soils killed the pumpkin. Sulfentrazone initially caused chlorosis and necrosis on pumpkin seedlings when soil organic matter was low (< 1%) or when soil moisture was high. However, plants recovered rapidly, and yields were not affected. In a greenhouse study pumpkin was more tolerant to clomazone plus sulfentrazone than to sulfentrazone.

Nicosulfuron and mesotrione are herbicides from different chemical families with different modes of action. An association between the sensitivity of sweet corn (Zea mays L.) to nicosulfuron and mesotrione was observed when hybrids, inbreds, and S1 families (S2 plants) were evaluated for herbicide sensitivity in field trials. In 2003 and 2004, 50% and 53% of mesotrione-sensitive hybrids were sensitive to nicosulfuron compared with only 6% and 1% of mesotrione-tolerant hybrids that were sensitive to nicosulfuron. In trials with inbreds in 2003 and 2004, 88% and 78% of nicosulfuron-sensitive inbreds had some injury from mesotrione but 0% and 5% of nicosulfuron-tolerant inbreds were injured by mesotrione. Among S1 families, 77% of the mesotrione-sensitive families were nicosulfuron-sensitive but only 5% of the mesotrione-tolerant families were sensitive to nicosulfuron. Segregation of S1 families for response to mesotrione was not significantly different from a 1:2:1 pattern of sensitive: segregating: tolerant families (chi square value = 2.25, P = 0.324) which would be expected if sensitivity was conditioned by a single recessive gene. Segregation of S1 families for response to nicosulfuron was 15:23:26 (sensitive: segregating: tolerant) which was slightly different from an expected 1:2:1 ratio (chi square value = 8.84, P = 0.012). Segregation of S1 families probably was affected by the relatively small number of S2 plants sampled from each family. Similar responses of the S1 families to nicosulfuron and mesotrione lead us to hypothesize that the same recessive gene is conditioning sensitivity to both herbicides. Possibly, this gene is common in the inbreds and hybrids that were sensitive in these trials. These hypotheses will be tested by examining segregation in S2 families and other segregating generations and by conducting tests of allelism among sensitive inbreds and inbred parents of sensitive hybrids. Chemical names: 2-(4-mesyl-2-nitrobenzoyl)-3-hydroxycyclohex-2-enone, (mesotrione); 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide, (nicosulfuron).

The effect of black and eastern black nightshade on the amount of photosynthetically active radiation (PAR) intercepted by a processing tomato canopy was studied along with the correlation between PAR and tomato growth and yield. During 1989 and 1990, black and eastern black nightshade were established at densities of 0 to 4.8 m−2within rows of transplanted, irrigated processing tomatoes. Increasing the density of either nightshade species decreased the number of tomato fruit; however, eastern black nightshade reduced tomato yield more than black nightshade. Eastern black nightshade was taller than the tomatoes, reducing PAR reaching the top of the tomato canopy. PAR reaching the top of the tomato canopy was positively correlated with yield and negatively correlated with eastern black nightshade density. Eastern black nightshade intraspecific competition decreased both stem and berry weight. Black nightshade was never taller than tomatoes and did not affect PAR reaching the top of the crop canopy. Increasing the density of black nightshade decreased berry dry weight but increased the weight of stems and leaves.

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