The agricultural community is currently involved in a debate with other members of society concerning many of the tools and tactics used to grow food. The discipline of weed science represents a microcosm of this larger societal debate, and thus is indicative of many other applied agricultural disciplines. Weed science comprises six fundamental disciplines, which have been arranged to depict its three major areas of research: weed technology, weed biology, and the ethics of weed control. Insight into those components of the debate that involve weed science is gained by examining each area. It seems unlikely that solutions to the “neckriddle” can be found through traditional research because of the integrative nature of agriculture, which involves environmental, economic, and social components. It is hoped that movement toward more holistic approaches to research will lead to resolution of the debate between society and the agricultural community.

An experiment was conducted at four locations during 1990 and 1991 to determine the response of cotton to 1.12 kg ai ha-1 of clomazone applied PPI in combination with in-furrow application of 0.50 kg ai ha-1 of aldicarb plus 0.14, 0.28, and 0.56 kg ai ha-1 of either disulfoton or phorate. Early-season cotton injury ranged from 15 to 63% with clomazone plus aldicarb. Stands were reduced 31 and 61% at two locations, and yield was reduced 50% at one location. Applied in combination with aldicarb, all three rates of disulfoton and 0.28 and 0.56 kg ha-1 of phorate protected cotton from clomazone injury. Phorate at 0.14 kg ha-1 partially protected cotton from clomazone injury.

Imazaquin at 140, 280, and 420 g ai ha-1 did not negatively affect seedling emergence from high vigor (98% germination) soybean seed but, coupled with a 5.0-cm herbicide incorporation depth, reduced seedling emergence from low vigor (67% germination) seed at all rates. Imazaquin at 420 g ha-1 incorporated 5.0 cm deep reduced low and high vigor seedling height 36 and 28%, respectively. Imazaquin at all rates reduced root length from high vigor seed, whereas only the high rate reduced root length of seedlings from low vigor seed. Although 420 g ha-1 metribuzin did not affect seedling emergence or root length, emerged seedlings were severely damaged when herbicide was incorporated to 5.0 cm. Trifluralin at 840 and 1680 g ai ha-1 reduced emergence of low vigor seed when incorporated 5.0 cm deep. Trifluralin at 840 g ha-1 did not affect seedling height or root length, but 1680 g ha-1 reduced height of seedling from low and high vigor seed by 86 and 66% when incorporated 5.0 cm deep. Trifluralin at 1680 g ha-1 reduced shoot dry weight of both types of seedlings only at the 5.0-cm incorporation depth.

Field experiments were conducted at two locations in 1989 and 1990 to investigate possible interactions between POST applications of primisulfuron and selected soil-applied carbamate and organophosphate corn insecticides. Insecticides were applied in-furrow at planting, at recommended use rates. Primisulfuron was applied POST to corn in the three- or five-leaf stage at 0, 20, 40, or 80 g ai ha-1. Combinations of primisulfuron with disulfoton, fonofos, isozophos, or terbufos resulted in foliar and root injury, plant height reductions, and yield losses. No foliar or root injury, plant height reductions, or yield losses were observed from combinations of primisulfuron and carbaryl, carbofuran, chlorpyrifos, or diazinon. Differences among and within the experiments are attributed to edaphic and environmental conditions at the time of primisulfuron application.

During 1989 and 1990, herbicides were applied to suppress common bermudagrass in a mixed stand of common bermudagrass and ‘Emerald’ zoysiagrass. When the mixed stand was treated with fluazifop at 0.2 kg ha-1 mid-May and 0.1 kg ha-1 1 mo later for two consecutive years, the common bermudagrass cover was reduced from 35 to 7% and the zoysiagrass cover increased from 65 to 85%. Similar results were achieve when fenoxaprop was applied at 0.2 kg ha-1 mid-May and repeated at monthly intervals for a total of four applications each year for 2 yr. The quality of mixed common bermudagrass and zoysiagrass turf was reduced immediately after each treatment; however, zoysiagrass recovered and treatments did not result in permanent damage. Sethoxydim suppressed common bermudagrass during the second year of treatment, but reduced the zoysiagrass stand each year. Ethofumesate applied along or with flurprimidol severely reduced the zoysiagrass stand with an increase of common bermudagrass.

Studies were conducted to determine whether cross-seeding of winter wheat, while maintaining an equal seeding rate per hectare, would increase wheat grain yields and help the wheat compete more effectively against Italian ryegrass than conventional seeding. Wheat was seeded at rates of 50, 100, and 150 kg ha-1 in conventional parallel rows or cross seeded in a grid pattern. Ryegrass was seeded at densities of 0, 20, 100, and 200 plants per m-2. Cross-seeded wheat yielded less grain than single-seeded wheat in 1990 in the absence of ryegrass; there were no differences in 1991. Cross seeding did not reduce competition from Italian ryegrass. Ryegrass was highly competitive against wheat, especially in 1990. Even 20 plants per m-2 reduced grain yield by an average of 38%. Wheat seeding rate had essentially no effect on grain yield in 1990, but the higher seeding rates reduced yields in 1991 because of extensive lodging. In 1991, wheat grain yields were higher in the cross-seeded plots than the single-seeded plots at the two high wheat seeding rates and highest ryegrass densities. Cross seeding does not appear promising as an aid to controlling ryegrass in Pacific Northwest wheat.

Herbicide efficacy was examined in the greenhouse on bigroot morningglory seedlings and on established plants in the field. Dicamba (0.14 kg ae ha-1) and 2,4-D (0.28 kg ae ha-1) alone or combined, glyphosate (2.24 kg ai ha-1), fluroxypyr (0.28 kg ae ha-1), and triclopyr (0.42 kg ae ha-1) controlled more than 90% of bigroot morningglory seedlings. Fluroxypyr (0.56 kg ha-1), triclopyr (0.84 kg ha-1), and 2,4-D (0.56 kg ha-1) alone or combined with dicamba (0.28 kg ha-1) reduced established stands in the field at least 50% within the season of application, whereas clopyralid (0.56 kg ha-1) did not provide acceptable control. Glyphosate (2.24 kg ha-1) was among the best treatments for long term control at all locations.

Several application modes and methods (schemes) of using herbicides are available to control undesirable vegetation on electric transmission line rights-of-way (ROW). Preferential use of a management scheme can be based on its cost effectiveness, i.e., degree of vegetation control and treatment cost. A treatment that increases/maintains desirable plants, decreases/maintains undesirable plants, and has relatively low cost, can be considered cost effective. Three common herbicides, 2,4-D, picloram and triclopyr, were applied in the field to test treatment mode (selective and nonselective) and method (cut stump, basal, and stem-foliar) effects on cost effectiveness during initial clearing and first and second conversion cycles on one electric transmission line ROW in Upstate New York. Clear or selective cutting with no herbicide was most cost effective during initial clearing. Nonselective and selective stem-foliar schemes were most cost effective during the first and second conversion cycles, respectively.

A four-year experiment was conducted near Urbana, IL to evaluate the effect of a rye cover crop on weed control, soybean yield and soil moisture. Soybeans were planted into either a rye mulch or corn stubble (with and without spring tillage). Giant foxtail, velvetleaf, smooth pigweed and common lambsquarters control in the rye mulch plots was generally greater than 90% and better than the corn residue treatments five weeks after planting. Weed control was generally better, except for lambsquarters, in the corn residue without spring tillage plots compared to the spring-tilled plots. Herbicides improved weed control in the corn residue plots but not in the no-till rye treatment, due to the excellent control by the rye mulch. Soil water content was lowest during June under the late-killed (killed at planting) rye during dry periods due to water depletion caused by the growing rye. During wet periods the rye mulch resulted in a wetter soil profile compared to the corn residue treatments. Soybean yields were reduced in late-killed rye compared to early-killed rye (killed 2 wk prior to planting) due to soybean stand reductions in the late killed rye. Yields in early-killed rye and spring-tilled treatments were similar to or better than soybeans planted in corn residue without spring tillage.

Field studies were conducted to evaluate common cocklebur control in soybean with imazaquin applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) at rates ranging from 24 to 140 g ai ha-1. With logistic regression analysis, predictions of common cocklebur control with imazaquin at 140 g ha-1 ranged from 92 to 95% (PPI), 87 and 92% (PRE), and 88 to 98% (POST) when rainfall was received for activation of PRE treatments and when weeds were not moisture stressed at time of POST application. When imazaquin was reduced to 70 g ha-1 under the same conditions, weed control was no higher than 88% PPI and 78% PRE. For all locations and years, common cocklebur control ranged from 79 to 91% for imazaquin POST at 24 g ha-1. Soybean yield was positively correlated with common cocklebur control (r = 0.66, P < 0.05).

Effects of linuron on annual bluegrass control and Kentucky bluegrass cultivar tolerance were studied in field and growth chamber experiments. In controlled environment experiments, linuron at 0.06, 0.12, 0.25, 0.50, and 0.75 kg ai ha-1 was applied to pure stands of annual bluegrass and eight Kentucky bluegrass cultivars. Linuron at the two highest rates controlled annual bluegrass, reducing the clipping dry weight by more than 85% 4 wk after treatment, and by 65 to 92% 6 wk after treatment. Growth of Kentucky bluegrass was reduced with the most severe reduction occurring 2 wk after linuron application. All cultivars exhibited normal growth 8 wk after treatment. In field experiments, linuron at rates from 1.5 to 2.0 kg ai ha-1 controlled annual bluegrass in old (> 5 yr) Kentucky bluegrass stands, and in 16 cultivars of 1-yr and 2-yr-old Kentucky bluegrass stands, with little or no damage. At rates of 1.5, 2.0, and 2.5 kg ai ha-1 linuron, damage to newly seeded cultivars was moderate to severe. However, 6 to 7 wk after linuron application to newly seeded cultivars, stand density and turf quality were equivalent to untreated checks.

The persistence of herbicide-resistant biotypes within a given weed population can be highly correlated with the longevity of its seed in the soil and its reproductive ability. This study compared seed longevity of sulfonylurea-susceptible (S) and -resistant (R) biotypes of prickly lettuce in soil at three depths and two locations. Seed longevity in soil was not different between R and S biotypes. Seed longevity was longer when seed were buried compared to seed placed on the soil surface. A field study on seed production showed that prickly lettuce plants produced an average of 14 flower heads and 181 seed per day. Average seed weight was 0.6 mg. No differences were observed in the fecundity or seed viability between the R and S biotypes. However, seed from R biotype plants germinated as fast or faster than seed from S biotype plants.

Field experiments were conducted at the Lacombe Research Station from 1989 to 1991 to determine the influence of various adjuvants on sethoxydim activity. In all experiments sethoxydim was applied at 100 g ai ha-1 to green foxtail, wheat, wild oat, and barley seeded in a canola crop. Of the four grass species, green foxtail was the most susceptible and barley was the least susceptible to sethoxydim. CC 16255 was the most effective adjuvant followed by either of two sources of ammonium sulphate (liquid or granular) and then Merge. Liquid and granular forms of ammonium sulphate were equally effective in enhancing sethoxydim activity. Several other adjuvants, including Enhance, Savol, and XE 1167, were moderately effective in the enhancement of sethoxydim activity. Adding Canplus 411 to Merge was not usually beneficial, but additions of Canplus 411 to Enhance often increased sethoxydim activity compared with sethoxydim and Enhance alone. Agral 90 and LI-700 were of little or no value as adjuvants with sethoxydim.

Field experiments were conducted from 1985 through 1989 to evaluate herbicide selectivity and impact on seeding-year yields of spring oat and underseeded alfalfa, and carryover weed control benefits from increased legume-fixed N for second-year dryland no-till corn. PRE metolachlor, pendimethalin, and prodiamine controlled green foxtail and POST bromoxynil or 2,4-DB controlled broadleaf weeds. These herbicides caused 0 to 20% alfalfa injury and 0 to 17% oat injury, and increased oat yield one of three years but did not increase the yield of underseeded alfalfa. POST pyridate, thifensulfuron, and tribenuron were too injurious to either oat, alfalfa, or both crops. Forage yields of annual ‘Nitro’ and perennial ‘Wrangler’ alfalfa seeded alone were greater than when they were underseeded in oat, with herbicides applied in both systems. As a result of drought in 1988 and 1989, yield of second-year corn planted after one-year alfalfa was not increased from potentially greater legume-fixed N. Dryland corn yield following monoculture oat or corn was 254% higher than corn following alfalfa.

The tolerance of canola to soil applied flurtamone was investigated in greenhouse and field studies. In the greenhouse, the dosage of flurtamone required to reduce canola fresh weight by 50% was 7.1- to 8.4- and 4.4- to 6.1-fold higher for B. napus and B. campestris cultivars, respectively, than that required to reduced wild mustard fresh weight by 50%. B. campestris cultivars tended to be more sensitive to flurtamone than B. napus cultivars. In the field, flurtamone applied at 0.4 to 0.5 kg ai ha-1 controlled 80% of wild mustard in canola (B. napus cv. ‘Westar’). In 1991 canola plant densities were reduced by increasing rate of flurtamone, but seed yields were unaffected by rate of application in either year.

Catclaw mimosa, an exotic member of the Leguminosae, occurs in three areas of Florida. Propagation is by seed only. Seeds collected from Florida were used for germination, growth, and herbicide evaluation studies. Seeds germinated at 75 to 94% but were not influenced by different environmental conditions under which they were stored. Greenhouse-grown plants cut or burned off at ground level failed to regrow. However, plants cut at 2 cm or more above ground level regrew from lateral shoots. Sixteen herbicides were evaluated to determine their effects on 6- to 8-wk-old plants grown in the greenhouse. Catclaw mimosa was killed by picloram, tebuthiuron, hexazinone and sulfometuron at 0.4, 0.07, 0.14, and 0.56 kg ha-1, respectively. Dicamba at 1.12, triclopyr at 1.12 (Garlon 3A and 4), linuron at 4.48, and glyphosate at 8.96 kg ha-1 were also effective. Chlorsulfuron and metsulfuron killed 9 out of 10 plants at the highest rates tested. Four herbicides, imazapyr, thifensulfuron, DPX-L5300, and atrazine killed 50% or less of the plants at the highest rates of each compound tested. Fosamine did not kill catclaw mimosa at the rates tested.

Field studies were conducted to study the interaction of sethoxydim or fluazifop-P with clopyralid and/or ethametsulfuron applied as tank mixtures to canola. Control of the indicator species barley, broadbean, and wild mustard with the tank mixtures was comparable to, or sometimes better than, that attained with each herbicide alone. Canola tolerated all herbicides applied individually and all tank mixtures of these herbicides except fluazifop-P and ethametsulfuron. Tank mixtures of fluazifop-P and ethametsulfuron, with or without clopyralid included in the mixture, suppressed early growth of canola in two of four tests and reduced seed yield in one. Sethoxydim, clopyralid, and ethametsulfuron combined in tank mixtures provide an effective POST alternative for selective control of grass and broadleaf weeds in canola.

Control of southern crabgrass by quinclorac was influenced by plant growth stage. A three-parameter nonlinear regression was used to describe the influence of quinclorac concentration on each growth stage and to compare growth stages. A SAS® program for these comparisons is described. Pseudo R2 values for fit were above 0.98 for all tests. Flowering crabgrass plants had the highest GR50 value (50% growth reduction on a dry weight basis) whereas preemergence, three- to five-true-leaf, and two- to four-tiller stages were lower.

Tebuthiuron, picloram, hexazinone, and bromacil were evaluated at 0.5, 1.0, and 2.0 g ai or ae per plant for sacahuista control on gravelly loam soils in western Texas. Tebuthiuron applied at 2.0 g per plant killed 87% of the sacahuista, which was significantly greater mortality than that achieved with the same rate of bromacil (62%) and hexazinone (44%). The 2.0 g plant-1 rate of tebuthiuron, bromacil, and hexazinone reduced live canopies of sacahuista 88 to 98%. Picloram did not control sacahuista. Sacahuista mortality increased curvilinearly with increasing rates of tebuthiuron and bromacil, whereas the response to hexazinone was linear.