Greenhouse experiments were conducted to determine whether multiple applications of glyphosate and time of glyphosate application with regard to the crop's growth stage had a significant effect on the growth and development of glyphosate-resistant canola. Glyphosate was applied as single applications at the two-, four-, or six-leaf stage of canola; as sequential double applications at the two- and four-, two- and six-, and four- and six-leaf stages of canola; and as a triple application at all three stages. Of the plant growth parameters measured, single applications of glyphosate resulted in significant reductions to stem weight and shoot weight compared with nontreated plants, and multiple applications of glyphosate caused significant reductions to leaf area, leaf weight, stem weight, and shoot weight. Single applications of glyphosate were less injurious to glyphosate-resistant canola compared with multiple applications, and canola growth parameter reductions were greatest after earlier glyphosate applications.

A field experiment was conducted near Davis, CA, during the 2003 and 2004 summer growing seasons to compare weed control, yield, and fruit quality in different irrigation and tillage systems in processing tomato. Trial design was a subplots with the main plots as subsurface drip irrigation or furrow irrigation, subplots were standard tillage or conservation tillage, and sub-subplots were herbicide or no herbicide. The hypothesis was that subsurface drip irrigation could limit surface soil wetting and thus inhibit germination and growth of weeds equal to or better than standard tillage and/or herbicides. In both 2003 and 2004, weed densities in the subsurface drip irrigation treatments were over 98% lower than the levels in furrow irrigation treatments. In addition, weed densities were lower in the subsurface drip–conservation till–no herbicide treatment than in any of the furrow irrigation treatments, including the furrow irrigation–standard tillage–herbicide treatments. The time required for a hand-hoeing crew to remove weeds was 5 to 13 times greater in furrow irrigation treatments compared to subsurface drip irrigation treatments. Weed biomass on beds at tomato harvest was 10 to 14 times greater in the furrow systems as compared to the subsurface drip irrigation systems. These results demonstrate the effectiveness of subsurface drip irrigation in controlling weed germination and growth, compared to tillage or herbicide applications. Tomato yield was higher in the subsurface drip irrigation treatment compared to furrow irrigation in 2004. Herbicide treatment increased yield in 2004, but only in the furrow irrigation treatment in 2003. Fruit brix level was not related to treatment in 2003, but was lower in the subsurface drip irrigation plots in 2004. These results indicate that subsurface drip irrigation can reduce weed competition in conservation tillage systems, without requiring herbicide applications.

Red rice is a major weed of rice in the southern U.S. and can intercross with rice. Knowledge of the plant phenotypes from such crosses would be valuable for identification and management of these plants. Male-sterile long-grain tropical japonicas ‘Kaybonnet-1789’ and ‘Cypress-1819’ were crossed with two awned and two awnless U.S. red rice types. F1 plants produced pubescent leaves, red pericarp, and medium-grain seeds. Crosses involving awned LA3 and TX4 red rice produced F1 plants with reddish-purple basal leaf sheaths and usually flowered within the same time periods as the parents, whereas those involving awnless StgS red rice had green basal leaf sheaths, flowered much later than either parent, and produced awnless F1 and F2 offspring. Crosses involving awned red rice produced F1 plants with long awns and F2 plants with awns ranging in length from zero to that of red rice parents. F1 plants were taller than either parent and produced intermediate culm angles similar to red rice, whereas F2 plants had culms ranging from erect (like rice) to more open than red rice. Thus, true F1 hybrids from crosses between pure breeding (homozygous) rice and red rice can be positively identified by a combination of traits including pubescent leaves, medium-grain seeds with red pericarps, open plant types, and heights greater than the red rice parent. F1 hybrids may be awned or awnless, have purple or green stems, or have normal or delayed heading. F2 plants have a broad combination of phenotypic traits found in both parents and F1 hybrids.

Volunteer potato is a perennial weed that is difficult to control in crop rotations. It was our objective to build a small, low-cost robot capable of detecting volunteer potato plants in a cornfield and thus demonstrate the potential for automatic control of this weed. We used an electric toy truck as the basis for our robot. We developed a fast row-recognition algorithm based on the Hough transform and implemented it using a webcam. We developed an algorithm that detects the presence of a potato plant based on a combination of size, shape, and color of the green elements in an image and implemented it using a second webcam. The robot was able to detect potatoes while navigating autonomously through experimental and commercial cornfields. In a first experiment, 319 out of 324 images were correctly classified (98.5%) as showing, or not showing, a potato plant. In a second experiment, 126 out of 141 images were correctly classified (89.4%). Detection of a potato plant resulted in an acoustic signal, but future robots may be fitted with weed control equipment, or they may use a global positioning system to map the presence of weed plants so that regular equipment can be used for control.

Weed management is a major production issue facing otebo bean growers in Ontario. Field trials were conducted at six Ontario locations during a 2-yr period (2003 and 2004) to evaluate the tolerance of otebo bean to the preplant incorporated (PPI) application of EPTC at 4,400 and 8,800 g ai/ha, trifluralin at 1,155 and 2,310 g ai/ha, dimethenamid at 1,250 and 2,500 g ai/ha, S-metolachlor at 1,600 and 3,200 g ai/ha, and imazethapyr at 75 and 150 g ai/ha. EPTC, trifluralin, dimethenamid, and S-metolachlor applied PPI resulted in minimal (less than 5%) visual injury and with exception of the low rate of dimethenamid causing a 16% reduction in shoot dry weight and the high rate causing an 8% plant height reduction had no adverse effect on plant height, shoot dry weight, seed moisture content, and yield. Imazethapyr applied PPI caused up to 7% visual injury and reduced plant height, shoot dry weight, and yield 8, 18, and 12% at 75 g/ha and 19, 38, and 27% at 150 g/ ha, respectively. Seed moisture content was also reduced by 0.4% with both rates. Based on these results, otebo bean is not tolerant of imazethapyr applied PPI at rates as low as 75 g/ha, the proposed use rate. EPTC, trifluralin, dimethenamid, and S-metolachlor applied PPI have a 2× rate crop safety margin for use in otebo bean weed management.

Field studies were conducted in 2001 and 2002 in the Black Sea Region of northern Turkey to determine the critical period for weed control (CPWC) in corn and the effects of weed interference on corn height. Treatments of increasing duration of weed interference and weed-free period were imposed at weekly intervals from 0 to 12 wk after crop emergence (WAE). The CPWC was determined with the use of 2.5, 5, and 10% acceptable yield loss levels by fitting logistic and Gompertz equations to relative yield data. With 5% yield loss level, the CPWC was 5 wk, starting at 0.2 WAE and ending at 5.2 WAE, which corresponded to the one- to five-leaf stage of corn. The CPWC increased to 8.9 wk, starting at 0 WAE and ending at 8.9 WAE, at the 2.5% yield loss level. At 10% yield loss level, the CPWC decreased to 1.7 wk, starting at 2.1 WAE and ending at 3.8 WAE.

A field experiment was conducted in 1996 and 1997 to determine snap bean tolerance to halosulfuron based on crop injury, height, and yield. Halosulfuron was applied preemergence (PRE), postemergence (POST), and sequentially PRE followed by (fb) POST at 35, 53, and 70 g ai/ha, respectively. For comparison, a hand-weeded check was included. When data were averaged across years and halosulfuron rates, halosulfuron PRE, POST, and PRE fb POST provided similar yellow nutsedge control (74 to 82%) at snap bean harvest. Halosulfuron PRE resulted in 4% snap bean injury at harvest. Similarly, halosulfuron PRE fb POST resulted in 5% injury, while halosulfuron POST caused the most damage at 8%. Snap bean height at harvest was reduced 14% with halosulfuron POST compared to the weed-free check, with only 5 and 6% reduction caused by halosulfuron PRE and PRE fb POST, respectively. Halosulfuron POST reduced yield 39% compared to the weed-free check, while the PRE and PRE fb POST application timings produced yield similar to the check. When averaged across years and halosulfuron application timings, an increase in halosulfuron rate had no effect on yellow nutsedge control or snap bean yield. A linear trend was found for snap bean injury and plant height at harvest with snap bean injury increasing with an increase in halosulfuron rate while snap bean plant height decreased with an increase in halosulfuron rate. Application of halosulfuron PRE is the safest means to control yellow nutsedge in snap bean in North Carolina.

A host-specific fungus Colletotrichum truncatum strain 00-3B1 (Ct) was mixed with herbicides to improve the control of scentless chamomile, a noxious weed in western Canada. The compatibility of Ct conidia (spores) with herbicides was evaluated in vitro, and varying effects were observed with different products on spore germination. Clodinafop, glufosinate, MCPA, and 2,4-D ester were relatively benign and delayed the germination slightly, whereas dicamba, imazethapyr, metribuzin, and 2,4-D amine were noticeably more inhibitive. Bromoxynil, glyphosate, sethoxydim, and Merge® (spray adjuvant) were most inhibitive, showing >50% inhibition after 24 h. To determine potential synergy, Ct was applied at 7 × 106 spores/ml in tank mixtures with selected herbicides at 1× and 0.1× registered rates under greenhouse conditions. Combining Ct with MCPA, 2,4-D ester, clopyralid, or metribuzin at 1× rate resulted in synergistic or additive interaction on scentless chamomile, increasing weed control significantly when compared to Ct or herbicides applied alone. Similar applications of Ct with imazethapyr, 2,4-D amine, dicamba, or glyphosate were antagonistic. Treatments with Ct plus 1× metribuzin killed scentless chamomile completely, whereas neither Ct nor the herbicide alone caused plant death, suggesting the value of this tank mixture.

Field studies were conducted at Fayetteville, Arkansas, to determine whether 47 Palmer amaranth accessions from different areas of the southern United States varied in response to postemergence applications of the registered rates of the isopropylamine salt of glyphosate (840 g ae/ha), fomesafen (420 g ai/ha), and pyrithiobac (70 g ai/ha). Glyphosate controlled all Palmer amaranth accessions at least 99% 21 d after treatment (DAT). Palmer amaranth control with fomesafen was equivalent for all accessions and at least 96% 21 DAT. Percent dry weight reductions were at least 92 and 94% for glyphosate and fomesafen, respectively. Palmer amaranth control with pyrithiobac was variable and ranged from 20 to 94% 21 DAT, but differences could not be attributed to accession origin. Herbicides with alternate modes of action from pyrithiobac should be utilized for Palmer amaranth control in regions where pyrithiobac has been used continuously.

Field experiments were conducted to evaluate the effect of five spray-nozzle types and three drift-control adjuvants (DCA) on glyphosate spray drift. The extended-range (XR) flat-fan nozzle at 280 kPa was used as the standard comparison. DCAs were evaluated for drift reduction with the use of the XR and air-induction (AI) nozzles. Wind speed ranged from 1.3 to 9.4 m/s (3 to 21 mph). Lethal drift (DL) and injury drift (DI) were determined by downwind visual observation of grain sorghum response. Drift distances were measured from the spray swath edge. The Turbo FloodJet and AI nozzles reduced DL distance by 34%. All four drift-reducing (DR) nozzles reduced DI distance by 22 to 32%. Reducing the pressure of the XR flat-fan nozzle from 280 to 140 kPa did not reduce DL or DI distance. When applied through AI nozzles, each DCA increased droplet volume diameter, one DCA reduced DI distance and none reduced DL distance when applied through XR tips. The DCAs did not affect DL or DI distance.

Research was conducted to evaluate root uptake, translocation, and metabolism of 14C-sulfentrazone alone or in a mixture with clomazone in solution in flue-cured tobacco transplants. Uptake and translocation of sulfentrazone was rapid and was not affected by the addition of clomazone. Fifty-nine and 65% of the 14C absorbed by the plant was translocated to the leaves within 24 h with sulfentrazone alone and in the clomazone plus sulfentrazone mixture, respectively. Differences in plant metabolism were observed between sulfentrazone alone and sulfentrazone plus clomazone. After 3 h, 66% of the 14C recovered from the leaves was metabolized when sulfentrazone was applied alone, compared to 91% when sulfentrazone was applied with clomazone. The difference could indicate that metabolism of sulfentrazone by tobacco transplants was enhanced by the presence of clomazone.

Greenhouse studies were conducted to determine the response of velvetleaf, common cocklebur, and ivyleaf morningglory to mesotrione and atrazine applied PRE, and to characterize the nature of any interaction between mesotrione and atrazine. Sensitivity to mesotrione was as follows: velvetleaf > common cocklebur > ivyleaf morningglory. Sensitivity to atrazine was as follows: ivyleaf morningglory > common cocklebur > velvetleaf. Combinations of mesotrione and atrazine resulted in at least an additive interaction. The activity of mesotrione and atrazine applied in combination was generally additive for control of velvetleaf and ivyleaf morningglory but was synergistic for several rate combinations.

Field trials were conducted in 2002 and 2003 at seven sites to determine the optimum rates of mesotrione and atrazine applied PRE for minimal crop injury and control of common lambsquarters, velvetleaf, Pennsylvania smartweed, common ragweed, giant ragweed, ivyleaf morningglory, and common cocklebur. All rates of each herbicide resulted in greater than 95% control of triazine-susceptible common lambsquarters. Mesotrione at 105 g ai/ha resulted in greater than 90% control of triazine-resistant common lambsquarters, velvetleaf, and Pennsylvania smartweed. Control of common ragweed was 90% or greater from mesotrione at 158 g/ha in combination with atrazine at 280 g/ha or greater. In addition, mesotrione at 210 g/ha combined with any rate of atrazine provided at least 92% control of common ragweed. Combinations of mesotrione and atrazine only suppressed, and did not effectively control, giant ragweed, common cocklebur, and ivyleaf morningglory.

Information on jointed goatgrass caryopsis development is currently lacking in published literature. It is hoped that through a better understanding of jointed goatgrass caryopsis ontogeny more effective weed-management strategies will be developed. Greenhouse experiments were initiated in fall 2002 and 2003 and completed the following spring seasons. Jointed goatgrass plants were started from spikelets, vernalized for 8 wk at 4 C, and grown in a greenhouse. Treatments were the number of days after anthesis (DAA) that a spike was allowed to remain on the plant before harvesting and ranged from 2 to 34 DAA, in increments of 1 (2002) or 2 (2003) d. Individual spikes were divided at harvest into three sections: top, middle, and bottom, disarticulated from the rachis, placed into a germinator, and germination recorded each day. Goatgrass spikelets germinated as early as 2 DAA, although spikelets harvested <7 DAA had <3% germination for all spike sections and were extremely variable, especially for the middle and bottom sections. Time to germination was similar for all sections of the spike. Maximum average germination of the top section was 72% compared with 86% for the bottom and middle sections. Our data suggest that factors other than developmental rate (i.e., dormancy) may affect germination in sections of the spike. A second year of the experiment was conducted for validation. Model validation suggested that although trends were similar in both years, variation in germination response might be too great for accurate, predictive model construction. The early germination shown in this research demonstrates that control measures must be implemented earlier than previously prescribed to prevent jointed goatgrass reproduction.

Field experiments were conducted to determine the effects of application timings and various herbicides on newly established ‘Coastal’ bermudagrass in 2001, 2002, and 2003. The experimental design was a split plot with three replications. Main plots consisted of three herbicide application timings of 1, 14, and 28 d after planting (DAP), and the subplots were 16 herbicide treatments. The hormone herbicides (picloram at 0.19 kg ae/ha + fluroxypyr at 0.19 kg ae/ha, picloram at 0.08 kg/ha + 2,4-D amine at 0.28 kg ae/ha, picloram at 0.15 kg/ha + 2,4-D amine at 0.56 kg/ha, 2,4-D amine at 2.2 kg/ha, 2,4-D amine at 1.2 kg/ha + dicamba at 0.42 kg ae/ha, and 2,4-D ester at 2.3 kg ae/ha) applied 1 DAP controlled large crabgrass 55 to 85%, did not injure Coastal bermudagrass sprigs, and aided establishment resulting in 22 to 27% ground cover in 2001 and 25 to 42% ground cover in 2002. Imazapic at 0.02, 0.035, and 0.05 kg ai/ha applied 1 and 14 DAP injured Coastal bermudagrass 5 to 45% across years, yet these plots had 20 to 54% ground cover compared with only 3 to 7% ground cover in the nontreated area in 2001, 2002, and 2003. The reduced rate of glyphosate (0.21 kg ae/ha) injured Coastal bermudagrass less than 8% and controlled large crabgrass 86 to 90% when applied 14 DAP, resulting in 43, 25, and 18% ground cover in 2001, 2002, and 2003, respectively. Trifloxysulfuron at 0.02 kg ai/ha applied 1 and 14 DAP did not injure Coastal bermudagrass sprigs, controlled junglerice 90%, and resulted in 73 and 52% ground cover, respectively. Coastal bermudagrass establishment was greatly increased when weeds were controlled.

An organic herbicide carrier could help reduce misapplication and environmental pollution associated with spray application of herbicides. Pellets prepared from landscape leaves that were dried, ground, and pelletized were evaluated as a preemergence herbicide carrier for container-grown ornamental plants. Isoxaben, pendimethalin, and prodiamine at rates of 1.12, 2.25, and 2.25 kg ai/ha, respectively, with either water or landscape leaf-waste pellets as a carrier were applied to chrysanthemum ‘Lisa’, spirea ‘Neon Flash’, and wintercreeper ‘Coloratus’. Common groundsel, common purslane, and giant foxtail were seeded following herbicide application. Leaf-waste pellets as a carrier produced equivalent efficacy and phytotoxicity ratings to conventional spray application of pendimethalin and prodiamine on both chrysanthemum and wintercreeper. The leaf-waste pellets were not an effective carrier for the application of isoxaben alone. The pellets had inconsistent effects on spirea phytotoxicity and growth.

A seedling bioassay was developed for the rapid diagnosis of resistance to clethodim and fluazifop-P in johnsongrass. The assay was based on differences in the coleoptile length of susceptible (S) and resistant (R) seedlings exposed to clethodim and fluazifop-P in petri dishes for 5 d. Bioassay concentrations of 0.09 mg/L clethodim and 0.18 mg/L fluazifop-P were chosen as discriminant based on rate responses of each biotype to increasing herbicide dose. At 5 d after treatment (DAT), the amounts of clethodim required to reduce coleoptile length by 50% (GR50) for the R and S seedlings were 462.5 and 24.8 mg/L, respectively, resulting in an R:S ratio of 18.7. The fluazifop GR50 values for the R and S seedlings were 618.7 and 17.5 mg/L, respectively, resulting in a R:S ratio of 35.4.

A study was conducted to evaluate weed control with imazethapyr applied at different timings or a combination of timings with or without an early POST application of bensulfuron, bentazon plus aciflurofen, bispyribac, carfentrazone, halosulfuron, propanil plus molinate, or triclopyr in drill-seeded imidazolinone-resistant rice. Control of barnyardgrass, red rice, and alligatorweed was insufficient with imazethapyr at 87 g/ha PRE or at 53 g/ha late POST alone. Imazethapyr at 87 g/ha PRE followed by imazethapyr at 53 g/ha late POST controlled red rice 86% or greater but did not control hemp sesbania. The imazethapyr PRE followed by late POST combination was also weak on barnyardgrass and alligatorweed early in the season. The addition of an early POST application of the other herbicides to the imazethapyr combination improved overall weed control, especially hemp sesbania control. Among the early POST herbicides, bispyribac, carfentrazone, or propanil plus molinate were more effective in helping improve the overall weed control, resulting in better rice grain yield.

Texas panicum is considered to be the most troublesome weed of field corn in the Southeast. Field trials were conducted in Georgia in 2003 and 2004 to compare pendimethalin, nicosulfuron, foramsulfuron, and glyphosate for Texas panicum control in irrigated field corn and to determine which herbicide provided the greatest economic returns. Pendimethalin applied early POST (EPOST), 10 to 12 d after planting (DAP), controlled Texas panicum less than 35% late in the season and resulted in reduced corn yield and net returns in 2004. Glyphosate applied sequentially POST at 21 to 24 DAP and again late POST (LPOST) at 35 to 38 DAP controlled Texas panicum 82 to 94% late in the season compared with 43 to 80% control by nicosulfuron and foramsulfuron applied POST. Texas panicum control, corn yield, and net returns were similar with glyphosate applied POST and LPOST at 0.53 or 1.1 kg ai/ha. Glyphosate applied POST and LPOST was more effective than glyphosate POST, but net returns were greater only in 2004.

Field research was conducted at Columbia and Novelty, MO, to determine the impact of winter-annual weed management systems on corn and soybean grain yields, winter-annual weed control, and soybean cyst nematode (SCN) egg population densities over the crop production cycle. Corn grain yield was not affected by winter-annual weed management systems. Soybean grain yield was not affected by winter weed management systems in 2001, but at Columbia in 2002 winter rye and Italian ryegrass reduced soybean grain yield 62 and 64%, respectively. Fall-applied simazine + tribenuron in corn and chlorimuron + sulfentrazone in soybean controlled winter-annual weeds greater than 99%. Fall-overseeded winter rye and Italian ryegrass in corn and overseeded Italian ryegrass in soybean controlled winter weeds 66 to 86%. In the soybean studies, race 4 SCN population densities increased (P = 0.08) in the nontreated control and remained stable (P = 0.55) with fall-applied chlorimuron + sulfentrazone from fall 2001 to spring 2002 while SCN population densities were reduced (P = 0.06) with spring-applied chlorimuron + sulfentrazone from fall 2002 to spring 2003. In the corn studies, none of the winter-annual weed management strategies reduced (P > 0.22) race 2 SCN population densities except winter rye from fall 2001 to spring 2002 (P = 0.05). This research indicates that control of weed species considered to be weak alternative hosts for SCN affected SCN population densities some instances when race 4 SCN population densities were high in a continuous soybean production system or race 2 SCN population densities were low in a 2-yr corn production system.