Season-long near complete weed control in sweet corn was achieved with preemergence (PREE) herbicide applications of pendimethalin (Prowl®), metolachlor (Dual®), or thiafluamide/metribuzin (Axiom®) followed by postemergence applications of bentazon (Basagran®) or dicamba (Banvel®). Basagran applied alone POST gave very good control ( >93 %) of lambsquarters (Chenopodium album) and purslane (Portulaca oleracea) but did not adequately control tumble pigweed (Amaranthus albus). Prowl applied alone PREE gave acceptable control of most weeds. POST applications of prosulfuron/primisulfuron (Exceed®) caused moderate corn injury by shortening internodes and overall plant height and slight foliar chlorosis.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

No description available.

The problems associated with short growing seasons has led to the development of leafy-reduced stature (LRS) corn hybrids. These hybrids have more leaf area above the ear, more rapid leaf area development, shorter stature, earlier maturity, and better responses to high plant populations and narrow spacings than conventional hybrids. Plants grown in a reduced light environment are limited in carbon assimilation and this, in turn, results in reductions in growth and development. A way to supplement the availability of photosynthate is injection of sucrose into plant stems. The objective of this thesis was to determine the ability of LRS corn plants to compete with weeds, and the reactions of weed species to the shade, including the relationships between weed growth (increase in biomass) and development (shape) under shaded conditions. Three years of field experiments (LRS and more conventional corn hybrids with both transplanted and naturally growing weeds) and two years of greenhouse work [weeds alone, C3 (lamb's quarters and velvetleaf) and C4 (redroot pigweed) in full sun or deep (75%) shade injected with 15% sucrose or not] were conducted. Yield reductions due to weed pressure were lower for LRS than other hybrids. Biomass production by both transplanted and naturally occurring weeds was up to 85% less under corn canopies than when grown without competition from corn. The biomass of C4 weeds was more reduced by competition with corn plants than that of C3 weeds. In spite of quick and early leaf development, leaves and other plant parts of LRS were not damaged excessively by mechanical (rotary hoeing) weed control. Both C3 and C4 weed plants produced more dry matter when injected with sucrose. Dry weights of sucrose injected shaded plants were not different from full sun uninjected plants. However, sucrose injection did not alter shading effects on development (distribution of biomass). Dry matter production and photosynthetic rates of C4 weeds were more reduced

No description available.

SC-0051 and SC-0774 are two experimental herbicides of undisclosed chemistry. A three year field study was conducted to evaluate SC-0051 and SC-0774 for weed control in conventional and no-till corn in Virginia. SC-0051 applied preemergence or postemergence, controlled common lambs-quarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.) horseweed (Conyza canadensis (L.) Cronq.), common chickweed (Stellaria media (L.) Vill. and was safe to corn. SC-0051 did not control smooth pigweed (Amaranthus hybridus L.) or giant foxtail (Setaria faberi Herrm.). SC-0774 effectively controlled the rye (Secale cereale) cover crop and large crabgrass (Digitaria sanguinalis (L. Scop.) but did not control broadleaf weeds or giant foxtail. SC-0774 also caused considerable but temporary corn injury when applied at rates above 1.1 kg/ha. Combinations of SC-0051 and atrazine provided broad spectrum weed control and yields comparable to atrazine plus metolachlor. Field and laboratory studies were conducted to evaluate the effect of soil pH on the soil mobility of SC-0051 and SC-0774 in sandy loam soils. SC-0774 was applied to soils amended to high and low pH and samples were collected by depth throughout the growing season. A method was developed for extracting and quantifying SC-0774 from collected soil samples. Large crabgrass was also used as a bioindicator species for qualitative detection of SC-0774 residues. These studies showed that SC-0774 was significantly more mobile in high pH soil than in low pH soil. Also, the decreased mobility of SC-0774 at low soil pH lead to decreased corn injury but it increased the soil residual activity of this herbicide. Soil column studies with SC-0774 and SC-0051 showed that the soil mobility of both herbicides increased with increasing soil pH. These herbicides cause reductions in chlorophyll and carotenoid levels in susceptible species resulting in a bleached appearance. The mechanism of this bleaching action is not known. Studies were conducted which examined the effect of SC-0051 on the pigment content and quantity in the susceptible species soybean. High performance liquid chromatography was used to separate, quantify, and identify pigments present in extracts of bleached tissues. The bleaching herbicide norflurazon was also examined for comparison purposes. SC-0051 and norflurazon inhibited the biosynthesis of carotenoids while causing an accumulation of the carotene precursor phytoene and an additional, unidentified pigment that appears to be structurally related to phytoene. This indicates that SC-0051, like norflurazon, inhibits carotenoid formation by blocking the desaturation of phytoene to phytofluene. The uptake and translocation of ¹⁴C-SC-0051 into tolerant corn and susceptible soybean seedlings was examined under growth chamber conditions to investigate the basis for the selectivity of this herbicide. Herbicide uptake was similar in both species but the susceptible soybean translocated a higher percentage of the ¹⁴C-SC-0051 to the growing point of new tissues than did the tolerant corn. It is proposed that differential translocation plays a role in the crop selectivity of the herbicide SC-0051. / Ph. D.

The potential of CGA-136872 (3-[4,6-bis(difluoromethoxy) pyrimidin-2-yl-1-(2-methoxycarbonyl-phenylsulfonyl) urea) and DPX-V9360 (3-pyridinecarboxaminde, 2-(((4,6-dimethoxy pyrimidin-2yl) aminocarbonyl)) aminosulfonyl) ))-N,N-dimethyl) were investigated for postemergence use in corn, including corn tolerance, weed control and combinations of CGA-136872 with other postemergence corn herbicides for weed control. CGA-136872 Applied at rates of 1.2, 2.5, 5.0 and 10.0 times the suggested recommended use rate in corn (variety Southern States 565) caused more injury at the 5-leaf stage than at the 7- and 9-leaf stage of corn. Recovery from injury was rapid and complete at 5 weeks after treatment (WAT) and no yield reduction was observed. Several corn varieties treated with twice the suggested use rate of CGA-136872 and DPX-V9360 showed injury that was both herbicide and variety dependent. Most injury occurred at 1 and 2 WAT. Corn recovery was complete at 5 WAT, but yield reduction on some varieties was observed with CGA-136872 treatments. In the weed control study, both herbicides showed high activity on johnsongrass (Sorghum halepense (L.) Pers.), giant foxtail (Setaria faberi Herr.), common lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.), particularly with early applications. However, johnsongrass rhizome regrowth prevented full season control of this species with early postemergence applications. Combinations of CGA-136872 with several other herbicides resulted in significant benefit in control of common lambsquarters and redroot pigweed while johnsongrass and giant foxtail control was not improved. Reduced control of johnsongrass was observed when CGA-136872 was applied in combination with paraquat (1,1’-dimethy1-4,4’-bipyridilium ion). Similar results were observed for giant foxtail control when CGA-136872 was applied with 2,4-D ((2,4-dichlorophenoxy) acetic acid) and dicamba (3,6-dichloro-2-methoxybenzoic acid). Results of this research indicate that both CGA-136872 and DPX-V9360 have good potential for postemergence use in corn, and could represent an important supplement to existing postemergence corn herbicides. / Master of Science

Field experiments were conducted at three Virginia locations in 1990 and 1991 to evaluate the effects of cover crop suppression method, nonselective herbicide, no-till cultivation, and herbicide banding on weed control, corn vigor, and corn yield. These factors were evaluated in experimental areas containing either a rye (Secale cereale) cover crop or in areas with no cover crop. In areas with a rye cover crop, the cover crop suppression methods evaluated were paraquat or mechanical suppression via mowing. In areas without a cover crop, paraquat was compared to a treatment without paraquat. Five selective herbicide treatments were evaluated within each level of the variable described above. These treatments included a control or no selective herbicides, a preemergence herbicide combination of atrazine plus metolachlor, and a postemergence herbicide combination of dicamba plus nicosulfuron. The preemergence and postemergence herbicides were applied either broadcast or banded over the crop row. The use of no-till, interrow cultivation was evaluated for each combination of the cover crop suppression method or nonselective herbicide and selective herbicide variables. Where a rye cover crop was present, paraquat significantly improved control of this species relative to mowing, and it provided significantly better control of most weed species and increased corn vigor and yield. In the absence of a cover crop, paraquat significantly improved weed control, but its effect on corn vigor and yield was dependent on weed pressure. Where weed pressure was moderate to heavy, paraquat significantly improved corn vigor and yield, whereas, it did not have a significant effect on these variables if weed pressure was low. In some situations, paraquat did not significantly improve late season weed control with broadcast selective herbicides, however, it provided quicker control of established weeds which significantly improved corn growth, especially in dry soil conditions. With or without a rye cover crop, cultivation did not significantly improve weed control, corn vigor, or corn yield when used with broadcast selective herbicides. Banded selective herbicides with cultivation provided weed control and corn vigor and growth equivalent to broadcast selective herbicides without cultivation if weed pressure was low. Where weed pressure is moderate to heavy, banded herbicides with cultivation did not perform as well as broadcast treatments without cultivation. Postemergence herbicides provided weed control and corn growth equivalent to preemergence herbicides, but use of effective nonselective herbicides at planting to control established weeds was critical. / Master of Science

The timing of weed emergence is of major importance for integrated weed management programs. If accurately forecasted, the timing of weed control operations could be optimized, enabling the implementation of more effective control strategies and consequently, the reduction of herbicide use. Little is known about weed emergence in Quebec. Weed emergence in the field results from the breaking of seed dormancy, seed germination and growth of the seedling to the soil surface. The purpose of this study was initially to review the environmental and cultural factors that affect these mechanisms, to determine which factors are mainly responsible for weed emergence in southwestern Quebec and, finally to develop a weed emergence model. This study focused primarily on common lambsquarters (Chenopodium album L.) and barnyardgrass (Echinochloa crus-galli [L.] Beauv.) since they were the most abundant weeds, representing 37 and 22%, respectively, of the total number of annual weeds in the experimental sites. A 3-year study established that the presence of corn did not affect the density and the pattern of emergence of these weeds. A 2-year experiment demonstrated that rainfall and irrigation had no or little influence on the pattern of weed emergence since soil water content was at or greater than field capacity in the spring. In Quebec, temperature was determined to be the most important factor regulating weed germination and emergence, meaning that weed germination is initiated by a minimal temperature in the spring and that this temperature is specific to each species. Thermo-gradient plate experiments established a base temperature for common lambsquarters, redroot pigweed (Amaranthus retroflexus L.), barnyardgrass, and green foxtail (Setaria viridis L.) of 4, 8, 11, 12 +/- 1 C and <3, >16, 12 and 12 +/- 1 C, respectively for seed lots originating from eastern and southwestern Quebec. These results served as a starting point for the calculation of thermal units for the

Mechanical weed control, chisel plow tillage and organic fertilization are important components of sustainable agriculture that can contribute to the preservation and improvement of soil and water resources. These practices can each affect weed communities, crop weed interactions and crop yields. Little is known about their combined effects on weed populations and weed community dynamics in common cropping systems. The main objective of this project was to determine the effects of crop rotation, weed control, tillage and nutrient source and their interactions on weed communities and weed emergence. The field experiment was conducted on a Sainte-Rosalie clay and a Duravin loam in Saint-Hyacinthe, Quebec, Canada, in 1996 and 1997. Mechanical control was not as effective as chemical control in controlling weed populations. Weed density increased after the second pass of the rotary hoe in soybean. Cultivation in corn triggered flushes of weed emergence, but corn yield was not affected by the increase in weed density. Chisel plow tillage reduced the efficacy of mechanical weed control in both crops. Reduced soybean yields were partly attributed to the large quantities of corn residues under chisel plow tillage. Nutrient source had no effect on weed densities. However, environmental stress conditions experienced in spring 1997 resulted in reduced crop growth and increased weed biomass under organic fertilization. Seed production of dominant residual weed species was greater under mechanical compared with chemical weed control, but was unaffected by tillage and nutrient source. Particular attention to weed management will be required when including both chisel plow tillage and organic nutrient source in a corn-soybean rotation, especially when resorting to mechanical weed control only.