Field experiments were established in 1989 and 1990 to determine the effects of application rate and timing on sicklepod control and soybean tolerance to POST applications of AC 263,222 and chlorimuron. When applied to 3-, 6-, or 10-leaf sicklepod, 35 g ai ha-1 or more AC 263,222 controlled more than 85% of sicklepod early in the season, and season-long when applied to 3- or 6-leaf sicklepod. At all timings, 70 g ha-1 or more AC 263,222 resulted in better control than a PRE application of 420 g ai ha-1 metribuzin followed by 9 g ai ha-1 chlorimuron applied POST. At 35 g ha-1 or more AC 263,222, application timing did not affect sicklepod control. However, control was reduced with 18 g ha-1 when applications were delayed from 3- or 6-leaf to 10-leaf sicklepod. At the 10-leaf sicklepod growth stage, a PRE application of imazaquin increased both sicklepod control and soybean yield with 35 g ha-1 AC 263,222 as compared with AC 263,222 applied alone. Soybean injury and height reductions with AC 263,222 at 35 g ha-1 and above were greater than with chlorimuron; however, increased soybean injury or height reduction was not reflected in pod numbers or yield.

Dogfennel is one of the most problematic weeds in Florida pasturelands and its control can become inconsistent as the plant matures. A premix of triclopyr + fluroxypyr has been recently introduced for weed control in pastures and rangeland; however, little published information exists concerning the control of dogfennel in pastures with this herbicide combination. Therefore, experiments were initiated to determine the efficacy of triclopyr + fluroxypyr compared with commonly used pasture herbicides on dogfennel at three heights. All herbicides utilized in this study are commonly used for dogfennel control. Dogfennel control was affected by both herbicide treatment and dogfennel height. In general, 0.80 + 0.28 kg ai/ha of 2,4-D amine + dicamba resulted in inconsistent control, especially as dogfennel plants increased in size. Increasing the rate of 2,4-D amine + dicamba to 1.21 + 0.42 kg/ha increased the consistency. Triclopyr + fluroxypyr provided similar levels of control as that of 1.21 + 0.42 kg/ha 2,4-D amine + dicamba. In all locations, control of 154-cm dogfennel was signficanatly lower than that of 38-cm dogfennel. These data indicate that triclopyr + fluroxypyr is an effective option for dogfennel control, but dogfennel height at the time of application is an important factor for optimizing control.

The objective of this WSSA Weed Loss Committee report is to provide quantitative data on the potential yield loss in sugar beet due to weed interference from the major sugar beet growing areas of the United States and Canada. Researchers and extension specialists who conducted research on weed control in sugar beet in the United States and Canada provided quantitative data on sugar beet yield loss due to weed interference in their regions. Specifically, data were requested from weed control studies in sugar beet from up to 10 individual studies per calendar year over a 15-yr period between 2002 and 2017. Data collected indicated that if weeds are left uncontrolled under optimal agronomic practices, growers in Idaho, Michigan, Minnesota, Montana, Nebraska, North Dakota, Ontario, Oregon, and Wyoming would potentially lose an average of 79%, 61%, 66%, 68%, 63%, 75%, 83%, 78%, and 77% of the sugar beet yield. The corresponding monetary loss would be approximately US$234, US$122, US$369, US$43, US$40, US$211, US$12, US$14, and US$32 million, respectively. The average yield loss due to weed interference for the primary sugar beet growing areas of North America was estimated to be 70%. Thus, if weeds are not controlled, growers in the United States would lose approximately 22.4 million tonnes of sugar beet yield valued at approximately US$1.25 billion, and growers in Canada would lose approximately 0.5 million tonnes of sugar beet yield valued at approximately US$25 million. The high return on investment in weed management highlights the importance of continued weed science research for sustaining high crop yield and profitability of sugar beet production in North America.

Almost 1,650 corn, cotton, and soybean growers in 22 states participated in a 2010 telephone survey to determine their attitudes with regard to which weed species were most problematic in glyphosate-resistant (GR) crop production systems for corn, cotton, and soybean. The survey is a follow-up to a previous 2005 to 2006 survey that utilized a smaller set of growers from fewer states. In general, growers continued to estimate weed populations as low and few challenges have been created following adoption of GR cropping systems. Pigweed and foxtail species were dominant overall, whereas other species were more commodity and state specific. Corn, cotton, and soybean growers cited velvetleaf, annual morningglory, and waterhemp, respectively, as predominant weeds. Growers in the South region were more likely to report pigweed and waterhemp (Amaranthus spp.), whereas growers in the East and West reported horseweed. When growers were asked with which GR weeds they had experienced personally, horseweed was reported in all regions, but growers in the South more frequently reported pigweed, whereas growers in the East and West regions more frequently reported waterhemp. Comparisons with the previous 2005 survey indicated that more growers believed they were experiencing GR weeds and were more aware of specific examples in their state. In particular, the Amaranthus complex was of greatest concern in continuously cropped soybean and cotton.

An in vivo ALS assay was used to differentiate between susceptible and resistant kochia biotypes from Idaho and Montana. Experiments were also conducted using this assay to determine the effect of the timing of herbicide application on ALS activity in resistant and susceptible cocklebur biotypes from Mississippi. When treated with chlorsulfuron, resistant kochia biotypes demonstrated 160-and 170-fold resistance at the whole plant level for the Idaho and Montana biotypes, respectively, compared to susceptible biotypes. Using the in vivo ALS assay, the Idaho and Montana biotypes showed 70- and 490-fold resistance, respectively, based on I50 values. The biotypes also demonstrated a low level of cross-resistance to imazethapyr using the in vivo technique. Resistant cocklebur biotypes showed approximately 200-fold resistance to imazaquin compared with susceptible biotypes. This research demonstrated that the in vivo assay can be used effectively to identify resistant biotypes 6 and 24 h after treatment, and to determine the extent of cross-resistance.

Common yarrow (Achillea millefolium L. ♯3 ACHMI) was called Achillea by the ancient Greeks (4), referring to the all-but-invulnerable Achilles who stormed Troy around 1200 B.C. According to legend (12), the centaur physician Chiron taught Achilles the benefits of this plant; the warrior then used yarrow to stanch the wounds of his compatriots during the siege of Troy. In fact, Achilles' knowledge of this herb may have provided him with the invulnerability which catapulted him into legend. Since the time of Achilles and the Trojan War more than 3000 yr ago, yarrow has been used to heal wounds and cure other ailments. Yarrow's legendary curative powers have a basis in chemical fact, as we will see.

Bahiagrass is used for roadsides, pastures, and lawns in the southeastern United States mainly because of drought and nematode tolerance. Metsulfuron is a sulfonylurea herbicide, which selectively controls bahiagrass in bermudagrass. Certain cultivars of bahiagrass were observed to be tolerant to recommended rates of metsulfuron. Therefore, research was conducted to investigate the susceptibility of five major bahiagrass cultivars to metsulfuron applied at increasing rates to 42 g ai/ha. Five bahiagrass cultivars were evaluated: ‘Pensacola’, ‘Tifton-9’, ‘Argentine’, ‘Common’, and ‘Paraguayan’. Argentine, Common, and Paraguayan cultivars showed a four- to fivefold increased tolerance to metsulfuron compared with Pensacola. Because of yearly inconsistencies, results for Tifton-9 were inconclusive.

Volunteer potatoes are difficult to control in onions and can greatly reduce onion growth and yield. Herbicides and cultivation were evaluated for control of simulated volunteer potatoes in onions in 1996 and 2000. Three interrow cultivations did not control potatoes in the onion row and the remaining plants reduced onion yield 50 and 73% compared with the hand-weeded checks. Three applications of oxyfluorfen (0.2 + 0.17 + 0.17 kg ai/ha) or bromoxynil plus oxyfluorfen (0.2 + 0.17 kg ai/ha) at the two-, three-, and four- to five-leaf stages of onions followed by a cultivation after each application reduced potato tuber weight 69 to 96% and tuber number 32 to 86% compared with cultivation alone and prevented onion yield loss associated with potatoes. Ethofumesate applied preemergence at 0.6 kg/ha followed by postemergence ethofumesate plus bromoxynil and cultivation reduced potato tuber weight 90% and tuber number 68% compared with cultivation alone, and onions yielded equal to hand-weeded checks. Two applications of fluroxypyr (0.3 kg ai/ha) plus bromoxynil (0.2 kg ai/ha) at the two- and three-leaf stages of onions followed by a cultivation after each application reduced potato tuber weight by greater than 90%, but onion yields were reduced 38 to 66%.

A scentless plant bug feeds on velvetleaf seeds. Fungi, dominated by the genera Fusarium and Alternaria, were isolated from insect-attacked seeds at levels related to insect density on the plants. The combined effects of insect feeding and fungal infection decreased seed germination. Burial of insect-attacked seeds in soil for 24 months reduced seed survival and increased Fusarium infection. Decreases in velvetleaf seed viability and survival in soil caused by a seed-feeding insect and associated seed fungi suggests that subsequent infestations by velvetleaf can be decreased through integrated use of the two biological control agents.

Blessed thistle is an important medicinal crop in Europe and recently has become more significant in North America. A limiting factor in blessed thistle production is weed interference. Field experiments were conducted near Plovdiv, Bulgaria, to study the effect of selected herbicides on weed control, crop productivity, and crop quality. Seed yields of blessed thistle were increased with metribuzin alone at 0.5 kg ai/ha, pendimethalin alone 1.32 kg ai/ha, pendimethalin at 1.32 kg ai/ha plus metribuzin at 0.5 kg ai/ha, trifluralin at 0.84 kg ai/ha plus linuron at 1.0 kg ai/ha, and in the hand-weeded control compared to the nonweeded control (nontreated check). Pendimethalin and metribuzin were safe both alone and in combination for weed control in blessed thistle. Bentazon at 0.96 kg ai/ha inhibited blessed thistle development and reduced seed yields compared to the untreated check. Generally, weed control increased the content of silymarin and decreased the amount of seed oil. Overall, seeds contained 0.26 to 0.36% taxifolin, 0.69 to 0.99% silydianin plus silycristin, 1.31 to 1.78% silybin, and 0.27 to 0.39 % isosilybin.

In a kiln experiment, temperatures of 200 to 400 C for 120 sec reduced germination of jointed goatgrass seeds 50 to 100%. Postharvest field burning of wheat and jointed goatgrass stubble destroyed 43 to 64% of the jointed goatgrass spikelets located on the soil surface. Seeds contained in spikelets that were minimally burned (slightly browned) germinated 32 to 65%, while seeds contained in spikelets moderately (less than 50% charred) and severely burned (greater than 50% charred) germinated 5 and 0%, respectively. Field burning destroyed 90% or more of jointed goatgrass seeds in spikelets located on the soil surface. Burning may be a feasible method for controlling small infestations of this weed.

Composted manure produced in deep-bedded hoop structures constitutes a source of nutrients and organic materials that can influence crop and weed emergence, growth, competitive interactions, and soil physical properties. The impact of composted swine manure on corn, soybean, winter wheat, velvetleaf, giant foxtail, and common waterhemp emergence and early growth were compared at compost rates of 0, 8, 16, or 24 Mg C/ha. Compost amendment had no effect on crop emergence but did reduce weed emergence. Inhibition of seedling emergence ranged between 15 and 57% for giant foxtail, 0 and 23% for velvetleaf, and 16 and 76% for common waterhemp. Soil amendment enhanced weed growth but not crop growth. A response surface regression analysis indicated that, while large-seeded crops have constant relative growth rates, small-seeded weed species increase their relative growth rates with compost amendment (P < 0.0001, r2 = 0.5252).

Invasive alien species (IAS) are a major threat to biological diversity on a global scale, necessitating international cooperation to address the problem. This paper gives the context in which action against IAS needs to take place, explains the need for international cooperation, and provides examples of key international instruments, strategies, and programs to deal with IAS.

Seeds from five suspected acetyl-CoA carboxylase (ACCase) inhibitor–resistant wild oat biotypes (R1 to R5) were collected in wheat and lentil fields in the Pacific Northwest. Based on whole plant dose–response experiments, the five resistant biotypes were 2 to 24 times more resistant to the aryloxyphenoxypropionate (APP) herbicides (fenoxaprop, diclofop, and quizalofop) compared with the susceptible biotype. However, none of the resistant biotypes were resistant to the cyclohexanedione (CHD) herbicides, sethoxydim and clethodim. R2 was the only biotype resistant to tralkoxydim and pinoxaden, a phenylpyrazolin herbicide and an ACCase inhibitor. The R2 biotype was 35 and 16 times more resistant to tralkoxydim and pinoxaden, respectively, when compared with the susceptible biotype. The levels of resistance and cross-resistance patterns varied among biotypes indicating either more than one mechanism of resistance or different resistance mutations in these wild oat biotypes. The CHD herbicides, sethoxydim and clethodim, could be used to control these resistant biotypes. Except for the R2 biotype, pinoxaden could be used to control the resistant wild oat biotypes. The resistance patterns of these wild oat biotypes are an indication of the difficulty in predicting cross-resistance among the ACCase inhibitor herbicides.

Dose-response experiments were conducted in a greenhouse on a biotype of johnsongrass from Washington County, Mississippi, to determine the level of resistance to the aryloxyphenoxypropionate (AOPP) herbicide fluazifop-P-butyl and the cyclohexanedione (CHD) herbicides clethodim and sethoxydim. Both seedling and rhizomatous plants were evaluated. Resistant/susceptible (R/S) ratios were calculated based on GR50 values (the rate required to reduce shoot dry biomass, expressed as a percent of the control, 50%). The GR50 values for the resistant and susceptible seedling plants were 110 and 10 g ai/ha for clethodim, 193 and 34 g ai/ha for fluazifop-P-butyl, and 265 and 48 g ai/ha for sethoxydim, resulting in R/S ratios of 11.0, 5.7, and 5.5, respectively. The GR50 values for the resistant and susceptible rhizomatous plants were 609 and 39 g/ha for clethodim, 657 and 29 g/ha for fluazifop-P-butyl, and 668 and 30 g/ha for sethoxydim, resulting in R/S ratios of 15.6, 22.7, and 22.3, respectively.

Transgenic, herbicide-resistant cultivars and equipment to spindle-pick 38-cm rows has renewed interest in narrow-row cotton production. Field experiments were conducted at four locations in North Carolina during 2004 and 2005 to evaluate weed management systems in glufosinate-resistant cotton planted in 38- and 97-cm rows. Weeds included broadleaf signalgrass, goosegrass, fall panicum, large crabgrass, Palmer amaranth, smooth pigweed, pitted morningglory, and tall morningglory. Greater than 90% control of annual grasses and Amaranthus spp. in 2004 and Ipomoea spp. in both years was obtained in narrow-row cotton with glufosinate applied early POST (EPOST) and mid-POST (MPOST) to two- and six-leaf cotton, respectively. With good early-season control by glufosinate and rapid canopy closure, there was little benefit from pendimethalin, fluometuron, or pyrithiobac applied PRE, S-metolachlor or pyrithiobac mixed with glufosinate applied MPOST, or trifloxysulfuron applied late POST (LPOST) to 11-leaf cotton in 2004. In 2005, with larger weeds at initial application, glufosinate EPOST and MPOST did not adequately control annual grasses and Amaranthus spp. Pendimethalin PRE increased control to greater than 90% and increased yields 59 to 75%. Pendimethalin PRE followed by S-metolachlor or pyrithiobac mixed with glufosinate at MPOST was no more effective than pendimethalin alone. Without PRE herbicides, trifloxysulfuron applied LPOST increased Amaranthus but not annual grass control. Cotton row spacing had no effect on cotton yield and little effect on weed control.

Field studies were conducted in 1996 and 1997 at Belleville and Pawnee, IL, to evaluate single and sequential applications of glufosinate on tolerance of glufosinate-resistant corn and annual weed control. Glufosinate caused 0 to 13% corn injury 7 days after treatment (DAT) and 0 to 6% corn injury 28 DAT. Injury was characterized as stunting with glufosinate. Glufosinate at 400 to 1,200 g ai/ha did not reduce final corn height or grain yield. At Pawnee in both years and at Belleville in 1996, a single application of glufosinate at 400 g/ha controlled giant foxtail, velvetleaf, ivyleaf morningglory, and common lambsquarters 85 to 100%. At Belleville in 1997, sequential applications of glufosinate provided greater weed control (87 to 100%) than a single application (0 to 63%) because of weed emergence after application. Weed control with a single application of glufosinate or with nicosulfuron plus bromoxynil was similar at both locations. Height and grain yield of glufosinate-resistant corn were not different from that of glufosinate-susceptible corn (isoline of glufosinate-resistant corn).

Field studies were conducted in the northern and southern cane belt areas of Louisiana to determine the effect of itchgrass on sugarcane growth and yield. Itchgrass was allowed to interfere with sugarcane season-long, early-season from emergence in the spring until layby (last cultivation) in mid-June, and late-season from layby until harvest. Itchgrass germination occurred throughout the growing season. Populations of millable sugarcane stalks and yields of cane and sugar were similar for no interference, early-, and late-season interference. Season-long itchgrass interference reduced sugarcane stalk populations and cane and sugar yields an average of 34, 42, and 43%, respectively, compared with no interference.

Competition from annual grasses and yellow starthistle can severely reduce perennial grass forage production and quality in pasture and rangeland. The purpose of this study was to determine yellow starthistle and weedy annual grass control by imazapic applied alone or in combination with picloram, and smooth brome tolerance to these treatments. Sixty days after treatment (DAT) imazapic applied at 70 and 140 g ae/ha reduced annual grass (downy brome, medusahead, and annual bluegrass) plant density and biomass by 66 to 76% compared with the untreated control. Picloram applied at 280 and 420 g ae/ha reduced yellow starthistle plant density and biomass by over 93%. Imazapic applied at 70 and 140 g/ha reduced smooth brome biomass by 79 to 95% at 60 DAT. Picloram did not affect the density or the biomass of annual grasses or smooth brome, whereas imazapic did not markedly affect the density or the biomass of yellow starthistle. Downy brome control increased to a maximum of 97% with increasing imazapic dose (maximum of 280 g/ha) at 30, 60, and 90 DAT.

Volunteer corn is often overlooked as a weed in soybean. To aid in management decisions, this study determined soybean yield loss attributed to volunteer corn and efficacy of various herbicides at several rates and timings. A hyperbolic equation estimated (R2 = 0.88) incremental yield loss (I) of 39.7% at low density when maximum yield loss (A) was constrained to 71%, the highest yield loss observed in these trials, revealing a more competitive plant than many common midwestern weedy species. Clethodim applied at 51 g ai ha−1 at V4 soybean resulted in > 90% volunteer corn control with < 5% soybean yield loss, whereas if applied at 12.7 g ai ha−1 volunteer corn control was 15%, but soybean yield was 50% greater than the nontreated control. On the basis of these data, the partial volunteer corn control improved soybean yield. Timing of glufosinate application influenced volunteer corn control. Glufosinate applied to 15-cm-tall corn resulted in 33% control, whereas applications to 36- to 91-cm corn resulted in > 70% control. Glufosinate combined with grass herbicides improved control to > 85%, with concomitant yield increases. Results demonstrated that volunteer corn substantially reduced soybean yield at low densities and yield increased when volunteer corn was controlled with various herbicides. On the basis of these results, and current soybean grain and herbicide prices, soybean yield gains from volunteer corn control could increase net return by > $150 ha−1.