Treerow vegetation abundance and biodiversity were measured in response to six orchard floor management strategies in organic peach in northern Utah for three growing seasons. A total of 32 weed species were observed in the treerow; the most common were field bindweed, dandelion, perennial grasses (e.g., red fescue and ryegrass), clovers, and prickly lettuce. Weed biomass was two to five times greater in unmanaged (living mulch) than in manipulated treatments. Tillage greatly reduced weeds for approximately one month; however, vegetation rebounded midseason. Tillage selected for species adapted to disturbance, such as common purslane and field bindweed. Straw mulch provided equivalent weed suppression to tillage in the early season. Straw required annual reapplication with material costs, labor, and weed-seed contamination (e.g., volunteer grains and quackgrass) as disadvantages. Plastic fabric mulch reduced weeds the most, but had high initial costs and required seasonal maintenance. Weed biomass declined within seasons and across the three years of the study, likely due to tree canopy shading. Neither birdsfoot trefoil nor a perennial grass mixture planted in the alleyways influenced treerow weeds. Our results demonstrate several viable alternatives to tillage for weed management in treerows of organic peach orchards in the Intermountain West.

Field studies were conducted from 1994 to 1996 in Michigan to evaluate postemergence (POST) herbicides for hemp dogbane control in corn. Studies were initiated at no-tillage and chisel-plowed sites each of the three years. Nicosulfuron and primisulfuron were evaluated alone and in combination with 2,4-D amine or dicamba. In 1995 and 1996, CGA-152005 plus primisulfuron was also applied alone and in combination with 2,4-D or dicamba. Control varied among years and sites. Nicosulfuron, primisulfuron, and CGA-152005 plus primisulfuron applied alone controlled 30% of the hemp dogbane, and dicamba or 2,4-D alone controlled 42 and 66%, respectively. Tank mixtures of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with dicamba were more effective and more consistent than dicamba alone. Combinations of nicosulfuron, primisulfuron, or CGA-152005 plus primisulfuron with 2,4-D gave the most effective and consistent control across sites, with an average of 93% control. In general, treatments controlled only shoots that had emerged at the time of application. New shoots emerged following herbicide application at the chisel-tillage sites in 1994 and 1995 but not at the no-tillage sites. However, in 1996, shoot emergence following treatment occurred in both no-tillage and chisel-tillage sites.

Clonal individuals from 16 hemp dogbane populations with phenotypic variation were analyzed using isozyme and randomly amplified polymorphic DNA (RAPD) analysis. Plants originated from populations in Michigan and Illinois. Three known Apocynum species, spreading dogbane, hemp dogbane, and prairie dogbane, were evaluated. Genetic distance among populations was more pronounced with isozyme analysis compared to RAPD analysis. The combined isozyme and RAPD analysis data separated spreading dogbane from all other plants analyzed. Genetic variation was present among the 16 hemp dogbane populations, but was less than expected based on the phenotypic variation present among the collections. The short genetic distance between the 16 hemp dogbane collections and the three Apocynum species suggests that variation among populations of hemp dogbane may be from outcrossing with other closely related Apocynum species. Isozyme and RAPD analyses were also conducted on plants from two populations in Michigan to determine the level of genetic variation among plants within the same population. Genetic analysis revealed that one population was entirely clonal, while the other population was a mixture of clonal and segregating plants.

Experiments were conducted to examine morphological variation among hemp dogbane populations. Rootstocks collected from 16 sites throughout Michigan and Illinois were used to establish nurseries in East Lansing, MI, and Champaign, IL. Growth, stem characteristics, and leaf characteristics were measured for each ecotype at both nurseries. Differences among ecotypes were observed for all measurements except emergence date and growing degree days to emergence. The number of shoots per plot produced by the ecotypes ranged from 5 to 54 and shoot height ranged from 69 to 126 cm. Ecotypes spread laterally at different rates, with the most aggressive covering 19 times more ground area than the least aggressive. Total shoot dry weight accumulation varied greatly among ecotypes. Some ecotypes could be identified from others by their unique leaf shape. Shoot number, shoot height, and ground area covered were greater for plants grown in Michigan than in Illinois. Differences in growth and morphological characteristics among ecotypes were not correlated with the geographical region where they were collected. Differences in measurements between the two nurseries illustrate the role of environment and genetics in the growth and morphology of this plant species.

Feral cereal rye is an aggressive, persistent winter annual grass. Although feral rye has been documented as a weed in Utah cropland for many years, it has only recently been described as a weed of natural areas in Utah. After feral rye was observed on hillside locations where it had not previously been present, research was conducted to evaluate expansion rates in isolated patches and on a landscape scale. Individual patch measurements indicated expansion rates of 17%, 42%, 44%, and 112% in 2009. The landscape expansion rates were 1%, 4%, 8%, 21%, and 50% in the same year. The spread of feral rye appears to have occurred primarily on south- to west-facing slopes where the density and diversity of native species is limited. The expansion of feral rye into natural, undisturbed areas indicates that this species should be closely monitored. The relatively short seed longevity and current small infestations make it a good candidate for early detection/rapid response efforts.

Land managers must set weed management priorities if limited resources are to be utilized effectively. Weed surveys and inventories assist land managers in this process by providing information regarding the identity, location, and relative abundance of weeds on their land. Although this information is vital, it can be challenging to select a method that provides the necessary data to meet management objectives while remaining accurate and cost effective. This paper critically evaluates four wildland weed mapping methods. These methods were defined as (1) paper-drawn, (2) buffered-point, (3) screen-drawn, and (4) perimeter-walked. Polygons were drawn by hand on topographic maps in the paper-drawn method. The other methods utilized handheld geographic positioning system (GPS) technology to digitally record infestations. Six experienced weed mappers independently recorded the location and size of eight sagebrush patches using each method. Time and accuracy were evaluated for each method based upon mapping time, distance walked, horizontal precision error, estimated size error, and shape error. The paper-drawn method was significantly less accurate than GPS-based methods at recording patch size and location. There was no significant difference in the accuracy of the buffered-point, screen-drawn, and perimeter-walked methods at reporting patch size and location. The need to cover land area quickly and efficiently favors the selection of the buffered-point or screen-drawn method because of time and distance factors. However, if patch shape is an important factor, the perimeter-walked or buffered-point methods may be the best choices of methods tested.

Yellow nutsedge infests a large number of hectares in the Treasure Valley of eastern Oregon and western Idaho. Much of its continued expansion appears to be related to onion production in the valley. Fall applications of metham often produce inconsistent results when used to control yellow nutsedge before planting an onion crop. Trials were conducted in the laboratory to determine the influence on yellow nutsedge control of metham dose, duration of exposure, temperature during exposure, and tuber conditioning by washing and chilling at 3 C. All factors influenced metham efficacy against yellow nutsedge tubers. The dose causing 50% reduction in sprouting tubers (I50) for metham ranged from 22 to 76 mg kg−1 of soil and was lower for conditioned tubers than nonconditioned tubers across all conditions, except when tubers were exposed at 25 C for 3 d. Nonconditioned tubers were unaffected by metham after 1 d exposure at 5 C. Increasing exposure temperature or increasing exposure duration decreased sprouting for nonconditioned tubers. As exposure duration and exposure temperature increased, differences among conditioned and nonconditioned tubers were less. Temperature and exposure duration affects metham efficacy against yellow nutsedge, and the condition of the tubers at the time of treatment also has a significant effect. Applications of metham at a time when yellow nutsedge tubers are not dormant may improve yellow nutsedge control.

Invasive weed management in wildland areas is often challenging due to the need to protect and preserve the integrity of natural ecosystems. Russian knapweed is an aggressive, deep-rooted, creeping perennial forb that was first identified as a problematic species in Dinosaur National Monument in 1977. From 2002 to 2005, extensive nonnative plant inventories were conducted in portions of the monument. Results were used to develop and implement an aggressive weed management program beginning in 2005. Emphasis was placed on reducing Russian knapweed infestations around Josie's Ranch in the Cub Creek Watershed. Several other species were targeted as well. In 2010, a reinventory was conducted in selected areas to evaluate how implemented management strategies affected the overall distribution and abundance of targeted species on the landscape. Comparisons between inventories indicate that management strategies were successful in reducing the total infested area of Russian knapweed by 79%. Treatments used for other targeted species also appear to have been effective in reducing their overall distribution and abundance on the landscape. In addition, the reinventory identified several new species with the potential to become problematic in the area. Although this case study documents the substantial progress that has been made at Dinosaur National Monument toward obtaining specific weed management objectives, it more importantly illustrates the process and benefits of an adaptive approach in sustaining long-term invasive plant species management efforts.

Goatsrue response to eight herbicide treatments was evaluated in greenhouse and field trials. Herbicides tested on goatsrue grown from seed in the greenhouse included 2,4-D amine, dicamba, chlorsulfuron, picloram, imazapyr, imazamox, aminopyralid, and triclopyr. Each herbicide was applied at rates of 0.125×, 0.25×, 0.5×, 1.0×, and 2.0×, where X is equal to the labeled rate. Goatsrue was most sensitive to the acetolactate synthase inhibitors chlorsulfuron and imazapyr, with 50% inhibition values of 0.07× (3.7g ai ha−1) and 0.16× (90 g ai ha−1) respectively. Goatsrue did not respond to increasing 2,4-D and imazamox rates. Herbicides evaluated in the greenhouse were also tested at two field sites (Smithfield and Amalga, UT), except imazamox, which was replaced by metsulfuron. Field studies gave some varying results, but overall showed that chlorsulfuron, metsulfuron, aminopyralid, and picloram gave at least 93% control at Smithfield, and 89% control at Amalga 24 mo after treatment (MAT). Treatments of chlorsulfuron, metsulfuron, aminopyralid, and picloram were also effective at increasing perennial grass cover at Smithfield 24 MAT. All treatments at Smithfield decreased seedling goatsrue cover, whereas only aminopyralid and picloram decreased seedling cover at Amlaga 11 MAT.

Previous research with annual weed species indicates that critical timing of weed removal begins primarily after the two-leaf stage of onion, a time when postemergence (POST) herbicides can first be applied. Volunteer potato is difficult to manage and persists in onion fields of western United States. The purpose of this research was to quantify the duration of volunteer potato interference on yield and market grade of onion as well as potato tuber production. Volunteer potato interference caused a 5% yield loss before onions reached the two-leaf stage, at two of three locations. Relative to weed-free plots, onion bulb diameter was reduced as duration of interference increased, resulting in smaller proportions of marketable bulbs. Volunteer potato produced daughter tubers shortly after emergence, which explains, in part, weed persistence despite removal of shoots with contact herbicides, cultivation, and hand-weeding in onion. Significant losses in onion yield and bulb diameter are likely given current volunteer potato management systems.

Field studies were conducted at Aberdeen, ID; Ontario, OR; and Paterson, WA, to evaluate potato tolerance to flumioxazin and sulfentrazone. In ‘Russet Burbank’ tolerance trials conducted in 2000 at ID, OR, and WA, sulfentrazone applied preemergence (PRE) at rates ranging from 105 to 280 g ai/ha caused significant injury consisting of stunting, leaf discoloration-blackening, and/or leaf malformation-crinkling at 4 wk after treatment (WAT). By 12 WAT, injury was ≤5%. At 4 WAT, flumioxazin applied PRE at 105 and 140 g ai/ha resulted in injury, whereas 53 g ai/ha did not cause significant injury. At 12 WAT, no visual injury was present at the ID site, whereas flumioxazin at 140 g/ha was still causing injury in WA. Regardless of initial injury, Russet Burbank tuber yields at ID, OR, and WA were not reduced as a result of any flumioxazin or sulfentrazone treatment compared with the nontreated controls. In potato variety tolerance trials conducted at ID in 2000 and at WA in 2002 with Russet Burbank, ‘Ranger Russet’, ‘Russet Norkotah’, and ‘Shepody’ and at ID in 2002 with those varieties plus ‘Alturas’ and ‘Bannock Russet’, early season injury caused by flumioxazin or sulfentrazone applied PRE at rates as high as 210 g ai/ha or 280 g/ha, respectively, occurred, but variety tuber yields were not reduced compared with nontreated control yields. In contrast, at ID in 2001, early injury caused by flumioxazin or sulfentrazone applied PRE at 105 or 210 g/ha translated to tuber yield reductions of all six varieties tested compared with the nontreated controls. At WA in 2001, Ranger Russet tuber yields were reduced by PRE applications of flumioxazin at 53 to 140 g/ha or sulfentrazone at 105 to 280 g/ha, and Shepody total tuber yields were reduced by all rates of PRE-applied sulfentrazone. Russet Burbank and Russet Norkotah tuber yields were unaffected by either herbicide. Unusual heat stress occurring early in the 2001 growing season at both locations may have compounded the effects of herbicide injury and, consequently, tuber yields were reduced in 2001, whereas injury occurring in 2000 or 2002 during relatively normal growing conditions did not translate to yield reductions.

Volunteer potato is highly competitive with onion and few control tactics are effective for removing this weed from an onion crop. Both volunteer potato density and duration of interference reduce onion yield, but the interaction of these factors is unknown. Field trials were conducted in 2003 in Idaho, Oregon, and Washington to determine the influence of volunteer potato density on the critical time of weed removal (CTWR) in onion. Yield losses of 2.5, 5.0, and 10% were estimated to occur at 534, 654, and 830 growing degree days (GDD) after onion emergence, respectively, with a volunteer potato density of 0.5 plants/m2. At 2.0 volunteer potato plants/m2, yield losses of 2.5, 5.0, and 10% were estimated to occur at 388, 481, and 598 GDD after onion emergence, respectively. Volunteer potato at 2.0 plants/m2 had to be removed at least one onion leaf stage sooner, compared to a weed density of 0.5 plants/m2, to avoid yield loss. Yield loss due to volunteer potato density or duration of interference was greatest among jumbo, colossal, and supercolossal market grades (P ≤ 0.1). Lowering potato tuber density in crops preceding onion will extend the critical time for weed removal and reduce the risk of crop loss.

Treatments of dimethenamid-p at 0.7 kg ai/ha applied PRE in tank mixtures with EPTC (3.4 kg ai/ha), metribuzin (560 g ai/ha), pendimethalin (1.1 kg ai/ha), or rimsulfuron (26 g ai/ha) were compared with the same herbicides applied PRE alone in field efficacy trials in Idaho, Oregon, and Washington. Common lambsquarters, kochia, and redroot pigweed control was generally improved with dimethenamid-p tank mixtures compared with control by any herbicide applied alone except metribuzin. Hairy nightshade control at two locations was generally improved with tank mixtures compared with control by any herbicide applied alone. At Washington, where row spacing was narrower than at other locations, dimethenamid-p alone or in tank mixtures provided similar hairy nightshade control, and this control was greater than control by EPTC, metribuzin, or pendimethalin applied alone. ‘Alturas’, ‘Bannock Russet’, ‘Ranger Russet’, ‘Russet Burbank’, ‘Russet Norkotah’, and ‘Shepody’ potato tolerance to dimethenamid-p PRE at 0, 0.7, or 1.4 kg ai/ha was assessed in weed-free field trials conducted at Aberdeen, ID, in 2002 and 2003. Little or no crop injury was evident during the growing seasons and there were no reductions in U.S. No. 1 and total tuber yields regardless of dimethenamid-p rate or potato variety.

Goatsrue is an introduced perennial plant which has proven to have great invasive potential, leading to its classification as a noxious weed in many states and at the federal level. Very little research has been done on its basic biology. Physical dormancy of mature goatsrue seed was tested through scarification with sulfuric acid for up to 60 min resulting in 100% germination. Comparison of dormancy for 26-yr-old and 6-mo-old goatsrue seed indicated that aged seeds had reduced dormancy levels compared to newly harvested seeds. Maximum germination was similar among the 6-mo old and 26-yr-old seed lots, suggesting no loss of viability had occurred in seed stored dry for 26 yr. Goatsrue seedling emergence was inversely related to burial depth, and decreased as burial depth increased. Emergence of seed buried at 0.5 to 3.0 cm soil depth was 93 to 87%, respectively, and no emergence occurred from 12 and 14 cm. When the soil seed bank of five goatsrue-infested areas was sampled, the largest density of seeds found was 74,609 seeds m−2 while the lowest was 14,832 seeds m−2. Viability and dormancy of seeds recovered from the soil seed bank survey ranged from 91 to 100% and 80 to 93%, respectively. Management, which reduces the soil seed bank and controls emerging seedlings, is as essential as control of mature goatsrue plants in order to avoid seedling establishment and reinvasion of a location.

‘Russet Burbank’ potato tolerance to dimethenamid-p applied preemergence at 0.7, 1.4, or 2.9 kg ai/ha was assessed in field studies conducted at Aberdeen, ID and Ontario, OR. Although crop injury was evident approximately 2 wk after treatment, most injury had diminished by row closure 2- to 3-wk later. Initial injury did not translate to yield loss and U.S. No. 1 and total tuber yields in dimethenamid-p–treated plots were similar to yields in the untreated, weed-free control.

Goatsrue is a member of the Fabaceae family, native to Europe and western Asia. It contains the toxic alkaloid galegine. The objective of the study was to describe galegine concentration in aboveground goatsrue plant parts and total galegine pools over phenological growth stages. Twenty goatsrue plants at four locations were selected and a stalk was harvested from each at five stages of phenological development and separated into parts. Plant parts were freeze-dried, ground, and analyzed with liquid chromatography/mass spectrometry. Galegine concentration was significantly different in plant tissues; reproductive tissues had the highest levels of galegine (7 mg g−1), followed by leaf (4 mg g−1) and finally stem (1 mg g−1) tissues. Galegine concentration and pools varied over plant tissues and phenological growth stages. Galegine pools (dry weight by concentration) or the total amount of galegine per stalk were lowest at the vegetative growth stage (2 mg stalk−1) and increased until reaching a maximum at the immature pod stage (91 mg stalk−1). The pools decreased nearly in half (48 mg stalk−1) by the mature seed stage. Like galegine pools, galegine concentration also reached a maximum at the immature pod stage (4 mg g−1), and decreased by nearly half by the mature seed stage (2 mg g−1). The increased levels of galegine pools at immature pod stage corresponds with the time of meadow hay harvest, implying that goatsrue is potentially most toxic at the phenological stage when it is likely to be harvested as a contaminant in meadow hay.

Growth and reproductive potential of individual yellow nutsedge plants were examined under two nitrogen levels and three soil moisture regimes. Irrigation levels were selected on the basis of irrigating at soil water potentials of −20, −50, and −80 kPa. Yellow nutsedge patch expansion was measured using digital images to determine ground cover, while plots were subsampled to estimate total shoot and tuber production. High nitrogen increased shoot production in 2004. When plots were irrigated at a soil water potential of −20 kPa, a single yellow nutsedge plant produced 3,000 and 1,700 shoots and 19,000 and 20,000 tubers in 2003 and 2004, respectively. Patch expansion at −20 kPa was exponential, with the greatest expansion occurring between the middle of July and mid to late August. This research demonstrates that the vegetative and reproductive potential of yellow nutsedge is greatly influenced by irrigation level. With such extensive growth and reproductive potential, management strategies for yellow nutsedge should focus on prevention, early detection and containment, early treatment, and integration of control strategies to reduce its competitiveness and spread.

Small burnet is a hardy, relatively long-lived evergreen forb with the potential to improve grazing lands, particularly to extend grazing into late fall and winter. Small burnet was evaluated for tolerance to spring and fall POST applications of aminopyralid, bromoxynil, clethodim, clopyralid, dicamba, dimethenamid-P, imazamox, metribuzin, pendimethalin, quinclorac, and 2,4-DB. Injury, seed yield, seed viability, and dry matter yield (DMY) were measured in the spring following application. Injury was observed in response to all spring and fall herbicide applications. Injury from aminopyralid was the highest for both spring and fall applications at 24 and 79%, respectively. Fall application of imazamox and dicamba resulted in 57 and 31% injury, respectively. Spring-applied aminopyralid and 2,4-DB both reduced DMY by 16%, whereas fall applications of imazamox, dicamba, and aminopyralid reduced DMY by 36, 12, and 67%, respectively. Fall applications of imazamox and aminopyralid reduced seed yield by 33 and 65%, respectively. Fall-applied aminopyralid reduced seed germination by 43%. None of the spring-applied herbicides affected seed yield or seed germination. Small burnet is severely injured by aminopyralid and to a lesser degree by imazamox and dicamba. Bromoxynil, clethodim, clopyralid, dimethenamid-P, metribuzin, pendimethalin, and quinclorac did not affect small burnet DMY, seed yield, or germination the year after application.

Bulb onions are poor competitors and volunteer potato, commonly observed in western USA onion fields, is difficult to manage. To improve the understanding of onion and weed interactions, relationships were quantified among volunteer potato density, onion yield, and volunteer potato tuber production using hyperbolic or linear models. Onion yield losses because of volunteer potato interference occur at densities commonly observed in the field. A volunteer potato density as low as 0.067 plants m−2 resulted in a 10% reduction in crop yield. Asymptotic yield loss (A parameter) was 100% and achieved with 4 volunteer potato plants m−2. Volunteer potato competition limits onion bulb size, resulting in a lower quality and thus a less-valuable crop. Volunteer potato tuber density and biomass increased linearly with initial weed density as high as 8 volunteer potato m−2. Onion yield loss from volunteer potato competition occurs to a greater extent and at a lower weed density than demonstrated in previous research on small-seeded annual weed species.

Greenhouse studies were conducted to determine the relative salinity tolerance of foxtail barley and seven desirable pasture grasses. Grass species were reed canarygrass, timothy, altai wildrye, tall fescue, tall wheatgrass, orchardgrass, creeping meadow foxtail, and foxtail barley. Grasses were exposed to increasing electrical conductivity levels of NaCl and CaCl2 salt solution over time. Grass species were compared using a cumulative value of salt exposure (ECdays), which was calculated to account for the electrical conductivity (EC) and the time a plant was exposed at that level of conductivity. Salinity tolerance varied among grass species. Increasing EC significantly reduced plant biomass of all species. All grass species experienced a 50% biomass reduction (GR50) between 271 and 512 ECdays in 2008 and between 297 and 575 ECdays in 2009. Foxtail barley was among the most salt tolerant (GR50 = 512 and 525 ECdays), requiring the highest salt exposure in 2008 and the second-highest exposure in 2009 to reduce biomass 50%. Grass mortality increased with increasing EC levels. Reed canarygrass and timothy were most susceptible to increasing salinity, with 50% mortality (LD50) of both grass species occurring between 983 and 1,186 ECdays. Moderate salinity tolerance was exhibited by orchardgrass, which required 1,977 and 1,844 ECdays; creeping foxtail, which required 1,998 and 2,431 ECdays; and tall fescue, which required 2,501 and > 2,840 ECdays to LD50 in 2008 and 2009, respectively. Foxtail barley, altai wildrye, and tall wheatgrass were most tolerant of salinity and persisted with little mortality occurring at 3,033 and 2,840 ECdays in 2008 and 2009, respectively. All grass species with higher growth rates than foxtail barley and altai wildrye were more susceptible to salinity, with the exception of tall wheatgrass. Growth rates of foxtail barley and altai wildrye were less than they were for other grasses, suggesting that slower growth rates may aid in salinity tolerance.