A field study was conducted to determine the effect of increasing seed rates of spring wheat (Triticum aestivum) on redstem filaree (Erodium cicutarium) biomass and seed production and on wheat yield in a zero-tillage cropping system. Wheat was sown at 50, 100, 150, 200, and 300 kg/ha in an experiment four consecutive years to determine annual and accumulated effects over time. Redstem filaree was most competitive with wheat when it emerged before or with wheat and when rainfall was plentiful during May and June. Redstem filaree biomass and seed production were markedly inhibited by drought conditions. An increase in wheat seed rate from 50 to 300 kg/ha reduced redstem filaree biomass and seed production by 53 to 95% over the years. There was little yield benefit to increasing the seed rate of weed-free wheat above 50 kg/ha. However, in the presence of redstem filaree, an increase in wheat seed rate from 50 to 300 kg/ha resulted in wheat yield being increased by 56 to 498%. Over four consecutive years, an increase in wheat seed rate from 50 to 300 kg/ha reduced redstem filaree in the soil seedbank by 79%. Higher seed rates of wheat can be an effective component of an improved program for redstem filaree management in conservation tillage cropping systems.

Field experiments were conducted to evaluate pyridine herbicides for Virginia buttonweed control and turfgrass tolerance. Treatments included clopyralid and fluroxypyr applied at 35, 70, 140, 280, and 560 g ae/ha, compared to a three-way combination of 2,4-D plus dichlorprop plus dicamba (840 + 840 + 210 g ae/ha, respectively). Fluroxypyr applied at 140 g/ha or greater controlled Virginia buttonweed 80% or greater through 10 wk after treatment. A second experiment evaluated 280 g/ha clopyralid or 140 g/ha fluroxypyr alone or in combination with 0.25 or 0.50% (v/v) nonionic surfactant, compared to 280 g/ha dicamba or 1,120 g/ha 2,4-D alone or in combination with nonionic surfactant. The addition of nonionic surfactant to clopyralid or fluroxypyr did not increase Virginia buttonweed control. Fluroxypyr at 280 g/ha and higher produced 22 to 53% injury to bermudagrasses 2 wk after treatment. Common centipedegrass was injured through 3 wk after treatment with 4,470 g/ha fluroxypyr or greater. Zoysiagrass exhibited injury with 4,470 g/ha fluroxypyr at 2 wk after treatment; however, injury was less than 8% at 3 wk. Common St. Augustinegrass was severely injured with 2,235 g/ha or greater fluroxypyr through 7 wk after treatment. Clopyralid did not cause injury to any turfgrass species.

Field studies were conducted under full-season conventional tillage in Delaware and New Jersey to determine the critical time to apply glyphosate with or without residual herbicides for optimum weed control in glyphosate-resistant soybean (GRS). The residual herbicides tank-mixed with glyphosate (0.84 kg/ha) were clomazone (0.55 kg/ha) and imazethapyr (0.063 kg/ha). Herbicide application was made at cracking, unifoliate, and one- to six-trifoliate stages of GRS. Weeds varied in growth stages from preemergence (PRE) at cracking to an average height of 30 cm at the six-trifoliate stage of GRS. Herbicide activity varied by year and weed species. Herbicidal action was better under high (>125 mm/mo) than low (<100 mm/mo) rainfall regime. Glyphosate application without residual herbicides was less effective at cracking and unifoliate than at one- to three-trifoliate leaf stages. Mixing residual herbicides with glyphosate at cracking and unifoliate stages enhanced weed control but made no difference when application was delayed until one- to three-trifoliate stages. For optimum weed control in GRS, the window of application for glyphosate alone was between the one- and three-trifoliate leaf stages, approximately 18 to 28 days after planting (DAP). If glyphosate was tank-mixed with residual herbicides, the window of application extended from cracking until the four-trifoliate stage; and weed interference until the four-trifoliate stage (approximately 32 DAP) did not depress GRS yield.

Lack of consistent regulation and marketing of adjuvants and complexity of the interaction among plant, herbicide, environment, water quality, and adjuvant have caused general confusion in adjuvant selection among growers. Choosing the best adjuvant is difficult. Growers must chose from thousands of commercial products and are confused by product descriptions with unfamiliar ingredients and functions. Confusing recommendations, aggressive marketing, and lack of unbiased research and educational information make matters even worse. Manufacturer lists of approved adjuvant products, guidelines that set minimum requirements to qualify adjuvants for use with herbicides, and packaging effective adjuvants with herbicides either in the herbicide formulation or packaged in a different container help reduce grower confusion. University adjuvant research and education have aided grower knowledge and understanding of adjuvants by field testing adjuvants and have influenced herbicide label wording and recommendations.

Reports of resistance to grass-selective herbicides, including johnsongrass (Sorghum halepense) resistant to fluazifop-P, have become quite common. Experiments were conducted to determine if fluazifop-P resistance could be transferred from johnsongrass to crop sorghum (Sorghum bicolor) and to identify the heritability of resistance in the progeny. A population of male sterile, fluazifop-P–sensitive sorghum, AKS-82, was interplanted with fluazifop-P–resistant johnsongrass and progeny treated with 0.105 kg ai/ha fluazifop-P postemergence (POST). Surviving seedlings were backcrossed to fluazifop-P–resistant johnsongrass. Viable plants from this successful cross were then testcrossed to another sensitive sorghum, TX622. These testcross progeny were then screened for herbicide resistance by again applying fluazifop-P POST at 0.105 kg /ha. Chi-square analysis revealed that resistance to fluazifop-P was inherited by a single, dominant gene. Natural hybridization of johnsongrass and sorghum is possible, and transfer of herbicide resistance between species can occur.

Field studies were conducted in Indiana, Michigan, Ohio, and Wisconsin in 1992 and 1993 to evaluate growth and response of common ragweed (Ambrosia artemisiifolia) to imazethapyr. Plants from ecotypes originating in each state were grown at all four locations. Nontreated plants grown in Wisconsin or Ohio were consistently taller than plants grown in Michigan or Indiana, regardless of the origin of the seeds. Nontreated plants originating from Wisconsin or Michigan showed a trend toward flowering earlier than those originating from Indiana or Ohio, regardless of test site. The results suggest the existence of common ragweed ecotypes based on origin of the seeds. Weather conditions after treatment with imazethapyr had a greater influence on common ragweed control and regrowth than the origin of common ragweed seeds. Common ragweed regrew following imazethapyr application through the development of axillary buds under conditions of warm temperatures and moist soils during the 4 to 6 wk following imazethapyr application. Mild to cool temperatures or dry conditions following imazethapyr application reduced treated common ragweed regrowth. Both early- and mid-postemergence imazethapyr treatments delayed flowering of all ecotypes. However, flowering of imazethapyr-treated plants followed the same order as nontreated plants, with plants from the Michigan or Wisconsin ecotypes showing a trend toward flowering earlier than those from Indiana or Ohio.

Understanding the effects of previous herbicide applications on cover crops is important if cover crops are to be successfully established during the same growing season. Greenhouse research was conducted to evaluate the sensitivity of annual ryegrass (Lolium multiflorum), oat (Avena sativa), crimson clover (Trifolium incarnatum), and medium red clover (Trifolium pratense) to EPTC plus R-29148, pendimethalin, and metolachlor plus CGA-154281 in a loam soil with 2.5% organic matter. Annual ryegrass density was reduced 96% by EPTC at 4.48 kg ai/ha and metolachlor at 2.24 kg ai/ha, whereas oat density was reduced 99% and 35%, respectively, from the two treatments. Pendimethalin at 1.68 kg ai/ha reduced annual ryegrass density 14%, but not oat density. Crimson clover biomass was reduced 33% by EPTC, 45% by metolachlor, and 15% by pendimethalin. All herbicides reduced the density of medium red clover > 25%, but biomass was reduced only by metolachlor. Field trials were conducted to determine whether persistence of these herbicides would affect the seeding time for annual ryegrass and crimson clover establishment. Annual ryegrass was successfully established following application of EPTC at 4.48 kg/ha when seeding was delayed 35 to 40 d after treatment (DAT). Pendimethalin at 1.68 kg/ha injured annual ryegrass > 15%, and annual ryegrass was severely injured by metolachlor at 1.68 kg/ha regardless of seeding time. Successful establishment of crimson clover following all herbicides was possible when seeding timings were delayed. Pendimethalin injured crimson clover less than 13% 15 to 17 DAT, and EPTC injured crimson clover less than 5% 28 to 35 DAT. Crimson clover injury from metolachlor was less than 16% 35 to 40 DAT. Herbicides with longer reported soil persistence generally require more time between herbicide application and cover crop seeding for safe establishment of the cover crop, particularly if the cover crop species is sensitive to the herbicide.

Adjuvant research contributes much to the knowledge and practice of weed science though the scientific process of systematically asking precise questions and subsequently making distinctions among alternative explanations. The purpose of adjuvant experimentation is to answer these questions and the purpose of associated papers and presentations is to communicate the new information. These purposes are self-evident, but are difficult to perfect. Some factors are particularly difficult for adjuvant researchers and require that researchers plan thoroughly from the formulation of the experimental question to final presentation of results. Adjuvant research requires both chemical and biological expertise that is traditionally separated in most organizations. Scientists from other disciplines or weed scientists not primarily concerned with adjuvants often direct adjuvant studies. This paper discusses mistakes that are commonly made in test design, interpretation, and presentation and suggests guidelines to improve the quality of adjuvant research.

Producers in the semiarid Great Plains are seeking management strategies to delay development of herbicide resistance. The objective of this study was to determine if cultural systems could control weeds in proso millet (Panicum miliaceum), thus eliminating the need for herbicides and removing selection pressure. Initially, we evaluated individual cultural practices for improving competitiveness of proso millet. Increasing seeding rate, banding N fertilizer with the seeds, growing a taller cultivar, and eliminating tillage favored proso millet over redroot pigweed (Amaranthus retroflexus). Combining several cultural practices with delayed planting in a cultural system reduced biomass and seed production of two pigweed species 85% or more in both tilled and no-till systems, subsequently eliminating proso millet yield loss. Density of the two pigweed species was sevenfold greater in the tilled system, yet the cultural system approach was still effective. Cultural system impact on seed production suggests that pigweed densities will not increase over time. With cultural systems, producers can minimize selection pressure, thus delaying development of herbicide resistance.

In Flanders fields the poppies blow
Between the crosses, row on row,
That mark our place; and in the sky
The larks, still bravely singing, fly
Scarce heard amid the guns below.

(In Flanders Field by Lieut. Col. John McCrae, who died in France on January 28, 1918, after four years of service on the Western Front)

The corn poppy (Papaver rhoeas L.), simple and enduring, has been a symbol of rural beauty and tradition for thousands of years. Artist John Ruskin (1819–1900) called it the most transparent and delicate of all the field blossoms (Haughton 1978). Other names for the species include field poppy, corn rose, pepper box, Flanders poppy, canker, redfield, and red poppy (de Bray 1978; le Strange 1977).

In greenhouse experiments, Ohio accessions of 22 weed species representing 13 dicot families were screened as alternative hosts of soybean cyst nematode (SCN, Heterodera glycines). Purple deadnettle (Lamium purpureum), henbit (Lamium amplexicaule), field pennycress (Thlaspi arvense), shepherd's-purse (Capsella bursa-pastoris), and a susceptible soybean (Glycine max) cultivar produced SCN population densities of 510, 155, 73, 1, and 366 cysts/450 cm3 soil, respectively, 5 wk after inoculation with eggs from a race 3 SCN population. Purple deadnettle was also a strong host of race 1 SCN and a weak host of race 6 SCN. Average numbers of eggs/cyst among race 3 hosts were highest in purple deadnettle (357), followed by soybean (292), field pennycress (266), henbit (122), and shepherd's-purse (none detected). To our knowledge, henbit is the only SCN host identified here that has been previously identified as a host. The weeds identified as SCN hosts in this study have a winter annual life cycle in Ohio and may serve as sites for SCN reproduction in infested fields during the early or late growing season and when soybean plants are absent.

Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to diclosulam applied preplant incorporated at 36 g ai/ha in a weed-free environment. Peanut cultivars evaluated included ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’,‘NC 9’, and the experimental breeding line N90010E. Visible injury 3 wk after planting was less than 5% regardless of cultivar. No injury was observed at 21 d after planting. Diclosulam did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Diclosulam did not affect percentage of extra large kernels, sound mature kernels, other kernels, and yield.

Field studies were conducted from 1996 to 1998 to evaluate grass control in no-till corn (Zea mays) with herbicides applied early preplant (EPP), preemergence (PRE), and postemergence (POST) at the Belleville Research Center at Belleville, IL. Grass control was affected by application timing rather than herbicide. The herbicides applied PRE provided more consistent giant foxtail (Setaria faberi) and barnyardgrass (Echinochloa crus-galli) control (90 to 98%) than the same herbicides applied EPP (0 to 92%). There also was no difference in giant foxtail and barnyardgrass control between the emulsifiable concentrate (EC) formulation and microencapsulated (ME) formulation of acetochlor. Rimsulfuron plus thifensulfuron applied POST provided 90 to 97% control of giant foxtail and barnyardgrass. Metolachlor, EC-acetochlor, SAN 582H, and rimsulfuron plus thifensulfuron provided 85 to 92% control of yellow nutsedge (Cyperus esculentus) compared with 63 to 74% control for BAY FOE 5043 plus metribuzin and ME-acetochlor. Corn grain yield was greater with herbicides applied either PRE or POST than applied EPP. Grass control and grain yield were greater with herbicides applied either PRE or POST compared with EPP.

The effect of seeding depth on emergence of red rice (Oryza sativa) ecotypes from Arkansas (AR), Louisiana (LA), and Mississippi (MS) was determined under dry-seeded rice production in clay and silt loam soils in Arkansas. By 21 d after planting (DAP), all red rice ecotypes had emerged from planting depths of 1.3, 2.5, 5.0, and 7.5 cm in both clay and silt loam soils. In silt loam soil, seedling emergence from 2.5 cm 7 DAP tended to be greater than from 1.3 cm in an early (normal temperature) planting. Also in this situation, the LA ecotype emerged more vigorously than the other ecotypes at all seeding depths and emerged from 7.5 cm at levels 1.5 times those of the other ecotypes at the same depth. In the clay soil, seedling emergence from 7.5 cm at 21 DAP was greater for the LA and MS ecotypes than for the AR ecotype in an early planting, but these differences were not observed for a late (elevated temperature) planting. Seedling emergence was earlier and greater in silt loam than in clay. The LA ecotype generally produced the greatest aboveground dry matter, especially at the early planting. The MS ecotype averaged 30% less dry matter production than the AR ecotype for the late planting in both soils. The ability of the LA and MS ecotypes to emerge from greater depths than the AR ecotype under certain soil and temperature conditions suggests that they could be more difficult to control with cultural practices used in dry-seeded rice culture.

Wild oat (Avena fatua) control often is an integral management practice in cropping systems that include cereal crops. Experiments were conducted at two locations in Saskatchewan (Saskatoon and Scott), Canada, from 1994 to 1997 to determine the influence of ICIA 0604 rate (50, 100, 150, and 200 g ai/ha), water volume (30, 50, and 100 L/ha), spray mixture pH (unbuffered, close to pH 7.0; reduced, pH 4.0), late morning and evening application times, and sodium bicarbonate concentration of water source (Saskatoon water, negligible; Scott water, 695 mg/L) on wild oat fresh weight and wheat (Triticum aestivum) grain yield. Reducing ICIA 0604 rate below the recommended label rate (200 g/ha) increased wild oat fresh weight by 22% and decreased wheat grain yield by 7% when applied with 50 or 100 L/ha of water. Applications with 30 L/ha of water resulted in more wild oat growth (19%) and less wheat yield (6%), regardless of the ICIA 0604 rates. Spray mixture pH or time of application did not modify the effects of ICIA 0604 rate and water volume on wild oat fresh weight and wheat yield at Saskatoon. At Scott, the negative effects of ICIA 0604 rates lower than 200 g/ha applied with 50 or 100 L/ha of water were most apparent when applications were made in the morning, especially with an unbuffered spray mixture. ICIA 0604 applications made in the evening with 50 or 100 L/ha of water resulted in the lowest wild oat fresh weights and greatest wheat yields, regardless of the ICIA 0604 rate or spray mixture pH. Antagonism between sodium bicarbonate in the unbuffered water from Scott, as indicated by the spray mixture pH effect, and the time of application effect were important factors controlling treatment responses at Scott. Lower than recommended ICIA 0604 rates often maintained net returns, even though wheat yield responded negatively to reduced ICIA 0604 rates. Understanding the effects of water quality on wild oat control will allow producers to make prudent decisions regarding the optimal application parameters for ICIA 0604.

Field studies were conducted in 19-cm-row soybean during 1997 and 1998 to evaluate the rate and timing of glyphosate applications applied alone at 0.42 and 0.63 kg ae/ha and with other herbicides to glyphosate-resistant soybean in terms of weed control, soybean yield, and net return. Weed species included barnyardgrass, hemp sesbania, pitted morningglory, and prickly sida. Among glyphosate-alone weed control programs, sequential applications generally provided the highest and most consistent control of all species evaluated (above 90% for broadleaf species). Glyphosate applied in combination with selective postemergence (POST) herbicides or following soil-applied herbicides controlled most species comparable to sequential glyphosate applications. Most herbicide programs, except for single glyphosate applications, were comparable to sequential glyphosate applications in terms of soybean yield and net return and ranged from 2,221 to 2,827 kg/ha and $410.28 to $549.60/ha. Depending on the year, either one or two glyphosate applications were needed for adequate weed control in programs with a soil-applied herbicide. Glyphosate rate affected neither weed control, yield, nor net return. Depending on a producer's management style and weed spectrum, weed control programs with glyphosate alone, in combination with another POST herbicide, or following soil-applied herbicides are all viable options in drilled glyphosate-resistant soybean.

Knowledge of optimal combinations of graminicide rate and stage of application could improve the effectiveness and net benefit of commonly used graminicides. A study was conducted at two locations in Saskatchewan, Canada, from 1994 to 1997. Factorial combinations of five graminicides (CGA 184927, fenoxaprop-p-ethyl, ICIA 0604, imazamethabenz, and flamprop-methyl), three graminicide rates (full, two-thirds, and one-third recommended label rate), and three leaf stages of wild oat (Avena fatua; two-, four-, and six-leaf) were compared to determine their effect on wild oat fresh weight, wheat (Triticum aestivum) seed yield, and net return. Wild oat fresh weight increased and wheat seed yield decreased to a greater extent at Saskatoon (median wild oat fresh weight of 56 g/m2) than at Scott (median wild oat fresh weight of 85 g/m2) when graminicide rate was reduced from the recommended label rate. Net return consistently decreased at both locations and among all graminicides when application rate was reduced from two-thirds to one-third of the recommended label rate. Imazamethabenz applied at progressively later growth stages caused greater wild oat fresh weight at both locations and reduced wheat yield and net return. Applying other graminicides at the earliest (two-leaf) stage of wild oat generally resulted in more or similar levels of wild oat fresh weight compared with delayed applications, especially at Saskatoon. With the exception of imazamethabenz, crop yield and net return were unaffected by leaf stage at both locations. The optimal graminicide rate is mostly dependent on the level of wild oat infestation, and the best time to control wild oat is dependent mostly on the particular graminicide.

Field research was conducted at three locations in Mississippi to evaluate CGA-277476 tank mixtures with four broadleaf herbicides for possible improvement of broadleaf weed control. Tank mixtures in this research were typically additive, although some instances of antagonism were noted. Control of morningglory (Ipomoea) species and hemp sesbania (Sesbania exaltata) was not consistently improved by the addition of acifluorfen, chlorimuron, fomesafen, or imazaquin to 59 or 79 g ai/ha CGA-277476. However, when a large population of weeds was present, the addition of acifluorfen, chlorimuron, or fomesafen to 59 or 79 g/ha CGA-277476 improved control over CGA-277476 alone. Prickly sida (Sida spinosa) was not controlled more than 68% with any treatment in this study; however, horse purslane (Trianthema portulacastrum) was controlled at least 90% with either 79 g/ha CGA-277476 alone or tank-mixed with acifluorfen, fomesafen, chlorimuron, or imazaquin. The addition of CGA-277476 to acifluorfen or fomesafen did not improve control over acifluorfen or fomesafen alone on any of the weeds evaluated; however, the addition of CGA-277476 to imazaquin improved hemp sesbania control over imazaquin alone. Tank mixtures did not result in yields greater than CGA-277476 alone in areas with moderate weed pressure, whereas in areas with severe weed pressure, tank mixtures improved soybean (Glycine max) yield over CGA-277476 alone.

To manage jointed goatgrass (Aegilops cylindrica), growers need an action threshold decision aid to assist them in deciding when to rotate to a spring crop instead of growing winter wheat (Triticum aestivum). A study was conducted in Washington from 1992 to 1995 to predict winter wheat yield loss based on a jointed goatgrass population in the previous year's winter wheat crop. To describe the relationship between jointed goatgrass density in year 1 and the resulting winter wheat yield loss in year 2, data were fitted to a rectangular hyperbolic model. First year jointed goatgrass densities in winter wheat of 1 to 5 plants/m2 led to a second year winter wheat yield loss of 3 to 30%. Yield loss was greater in a dry year than in a normal to wet year. To initiate an action threshold for jointed goatgrass successfully, growers need to incorporate data from this study with their knowledge of yield potential, price dockage of the subsequent winter wheat crop, and profitability of alternative spring crop rotations.

Field experiments were conducted at Vegreville and Lacombe, AB, to determine the influence of barley (Hordeum vulgare) variety and seeding rate on interference of wild oat (Avena fatua) with barley. Barley variety and seeding rate affected barley density, height at maturity, and seed yield, as well as wild oat shoot dry weight and seed yield in most experiments, but there was no variety by seeding rate interaction. As expected, the semidwarf varieties Falcon and CDC Earl were the shortest. Barley seedling emergence and subsequent plant densities varied among varieties, locations, and years. The hull-less varieties Falcon and CDC Dawn had the poorest emergence in most cases, whereas AC Lacombe and Seebe had the highest emergence. Wild oat shoot dry matter and seed production was highest in the Falcon, CDC Dawn, and CDC Earl plots, suggesting that these were the least competitive with wild oat. Barley yield loss from wild oat interference also tended to be highest in these varieties. Poor emergence of Falcon and CDC Dawn and the shorter stature of Falcon and CDC Earl likely contributed to their relatively poor competitiveness with wild oat. Increasing the seeding rate improved the competitiveness of all varieties, as evidenced by reduced wild oat shoot dry matter and seed production and, in some cases, improved barley yields.