Optimal time of application of the isopropylamine salt of glyphosate for long-term control of foxtail barley was studied near Delta Junction, AK in 1992 and 1993. Applications of either 0.6 or 1.1 kg/ha of glyphosate with 2.2 kg/ha of ammonium sulfate and 0.5% (v/v) nonionic surfactant were made to different foxtail barley plots at approximately 2-wk intervals from May to September. Control was rated in July of the year following application. The 0.6 kg/ha rate produced ≤ 60% control on all application dates. At 1.1 kg/ha, foxtail barley control was best from applications made between early August and mid-September. May and mid-June applications provided up to 80% control in 1993 but ≤ 50% control in 1992. For both rates, applications made from late June through July, during foxtail barley flowering and seed fill, consistently provided little control (< 50%).

Adsorption and desorption of metribuzin and metolachlor were studied for 0- to 15- and 30- to 45-cm soil depths and at 5 and 28 C temperatures for two subarctic Alaskan agricultural soils. Surface soils had five to eight times the organic carbon content of deeper soils and had lower Freundlich isotherm slopes (1/n) for both herbicides. Surface soil Freundlich coefficients (Kf) were affected by both soil type and equilibration temperature, with soil type accounting for greater than 80% of the variation in Kf. Surface soil mean Kf values ranged from 1.5 to 2.4 for metribuzin and 4.4 to 9.2 for metolachlor. For soils from the 30- to 45-cm depth, neither soil type nor temperature affected Kf. Isotherm slopes for desorption were less than adsorption, indicating hysteresis. Regressions between desorption Kf and maximum herbicide adsorbed prior to desorption were highly significant with coefficients of determination (r2) between 0.50 and 0.99.

A 50-year study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seed were buried in mesh bags 2 and 15 cm deep and were exhumed 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, and 9.7 yr later. Viability was determined by germination and tetrazolium tests. All common hempnettle and quackgrass seed were dead after 2.7 and 3.7 yr, respectively. Less than 1% of wild oats and foxtail barley seed were viable after 3.7 yr, but > 6.7 yr were required for loss of all viability. By 9.7 yr, < 1% seed viability remained for: bluejoint reedgrass, corn spurry, pineappleweed, prostrate knotweed, and wild buckwheat From 2 to 5% of seed from common chickweed, common lambsquarters, flixweed, Pennsylvania smartweed, rough cinquefoil, marsh yellow-cress and shepherd's-purse were viable, while 62% of American dragonhead seed was still alive. Seed longevity in agricultural fields is not greater under subarctic conditions than under warmer conditions.

The effect of common lambsquarters (Chenopodium album L. #3 CHEAL) density on spring barley (Hordeum vulgare L. ‘Lidal’) was studied in a 2-yr field experiment near Fairbanks, AK. The data were fit to a rectangular hyperbola model. Common lambsquarters densities explained 74 to 75% of the variability in barley yield. The maximum yield loss attributable to common lambsquarters was 23% in 1982 and 36% in 1983.

A method is presented to determine which of a set of sampling techniques is most nearly optimum for sampling weed abundance. To employ the method, one needs first to develop a set of sampling alternatives. A pilot survey is then conducted to determine time costs and sampling and measurement error variances associated with each technique. We used this method to determine which of three plot sizes (0.6 by 0.6 m, 0.6 by 1.5 m, 1.2 by 2.1 m) and two types of orchard scans is most nearly optimum for estimating weed abundance in apple [Malus domestica (Bork)] orchards. The results indicate that, for weed species that are fairly apparent, orchard scans are optimal when less than 8 h of sampling effort is expended, but when a high degree of precision is required, or when the weed species is more difficult to detect, plot samples may be the better choice. A size of plot ca. 0.6 by 1.5 m size was found to be most nearly optimum.

The general appearance of plants was similar for 14 accessions of velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH) obtained from Stoneville, MS (33° 25’ N), Rosemount, MN (44° 43’ N), and various locations in between. All accessions were equally susceptible to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Variation in maturity characteristics was found among the accessions in the field at Rosemount; southern accessions began seed capsule production later and continued it longer than did northern accessions. Velvetleaf accessions from Stoneville and Rosemount both produced seeds in the field at Weslaco, TX (26° 09’ N), but at Fairbanks, AK (64° 49’ N), neither accession produced seeds before being killed by frost.

A 50-yr buried-seed study was initiated at Fairbanks, AK, in 1984. Seed of 17 weed species important in Alaskan agriculture were collected and buried 2 and 15 cm deep. Seed viability was determined initially and after recovery from the soil through a combination of germination tests and 2,3,5-triphenyltetrazolium chloride (TTC) treatments. Seed exhumed at 9 and 21 months were tested for viability and dormancy. Burial depth had a significant effect on seed longevity of corn spurry (Spergula arvensis L. # SPRAR), wild oats (Avena fatua L. # AVEFA), pineappleweed [Matricaria matricarioides (Less.) C. L. Porter # MATMT], and bluejoint reedgrass [Calamagrostis canadensis (Michx.) Nutt.]. Viability was higher for seed buried at 15 than at 2 cm. Viability of shepherdspurse [Capsella bursapastoris (L.) Medik. #CAPBP] and pineappleweed seed did not decrease significantly over the 21-month burial period. In contrast, seed viability of wild buckwheat (Polygonum convolvulus L. # POLCO), common hempnettle (Galeopsis tetrahit L. # GAETE), wild oats, quackgrass [Agropyron repens (L.) Beauv. # AGRRE], and foxtail barley (Hordeum jubatum L. # HORJU) was less than 11% at the end of 21 months. There was no significant relationship between initial seed dormancy and viability after 21 months of burial.

Vegetative cover of weeds was determined in 84 agricultural fields representing a number of crops in Alaska. Multivariate statistical techniques were used with weed, soil, and management data to determine if weed vegetation was related to particular environmental and management variables. Field age was the variable that best explained the variation in vegetation composition. In fields recently cleared, native species were most important, being replaced by introduced weed species with increasing field age. Field horsetail (Equisetum arvense L.) was an exceptional native species that persisted under cultivation. Total weed cover was low in the first few years of cultivation, but increased as introduced species such as common lambsquarters (Chenopodium album L.), common chickweed [Stellaria media (L.) Cyrillo], quackgrass [Agropyron repens (L.) Beauv.], and foxtail barley (Hordeum jubatum L.) became more prevalent. A number of introduced species such as hempnettle (Galeopsis tetrahit L.) and Pennsylvania smartweed (Polygonum pensylvanicum L.) were restricted to just a few fields, emphasizing the importance of using weed-free seed and other management practices to minimize the spread of introduced weeds.

Seed of 17 weed species that were buried at 2 and 15 cm at Fairbanks, AK, in 1984 were exhumed at 1-yr intervals and tested for germination and viability. Burial depth had a significant effect on seed viability of wild oats, bluejoint reedgrass, quackgrass, prostrate knotweed, and corn spurry with viability remaining higher at 15 than at 2 cm. The percent of viable foxtail barley and quackgrass seed that were dormant was greater at 15 than at 2 cm. Eleven of 17 species had greater than 6% seed viability 4.7 yr after burial. American dragonhead seed viability in 1989 was not significantly lower than in 1984. In contrast, viability of common hempnettle and quackgrass had dropped to zero by 2.7 and 3.7 years after burial, respectively. Foxtail barley and wild oats had less than 1% viable seed at the end of 4.7 yr. For most of the 17 species, a rectangular hyperbola model accounted for more of the variability in seed viability decline with time than did a negative logarithmic model.

Soil samples representing a time series from forest before clearing to land in cultivation for 20 yr were taken near Delta Junction, AK, to determine the changes that occur in the soil seed bank following clearing and agricultural use. The total number of seed was initially low in the forested sites but increased after 3 to 5 yr in cultivation due to seed production by native colonizers and by introduced weeds such as common lambsquarters (Chenopodium album L. ♯3 CHEAL). Viability of seed of several mature forest species was low. There was a shift from a seed bank dominated by native species in the forest and newly cleared sites to a seed bank dominated by introduced colonizers in the older fields. Although seed of introduced species increased in importance over time, native species, especially native colonizers, continued to be an important component of the seed bank throughout the 20-yr period represented.

Optimal rates and time of application of glyphosate for control of the native perennial bluejoint reedgrass [Calamagrostis canadensis (Michx.) Nutt.] were determined from 1986 to 1989 near Delta Junction, AK. Applications were made 2 wk apart from late May or early June to September. Glyphosate did not provide control before June 15 or after September 1. Bluejoint reedgrass was controlled best when glyphosate was applied from late July to mid-August. Ammonium sulfate (2.2 kg ha-1) or nonionic surfactant (0.5% v/v) increased control except on the earliest and latest application dates. Control was consistently better with 1.1 than 0.6 kg ha-1 (ai) of the isopropylamine salt of glyphosate.

Invasive plants disperse to new areas via numerous pathways. Study of these pathways helps to focus limited budgets toward prevention and early detection. This study examined potentially invasive seed contaminants in imported crops and grass seed as pathways for plant dispersal to Alaska. Crop and grass seed were purchased from 13 Alaska retail outlets representing 14 seed suppliers. Seed bags were sampled using federally mandated protocols and were analyzed for crop seeds that were not supposed to be included and for weed contaminants. Ninety-five weed and 36 contaminant crop taxa were found. Crop seed contained 43 weed taxa and 15 other crop species contaminants, a mean of 6.4 taxa and 3,844 contaminant seed kg−1. Grass seed samples contained 73 weed taxa and 21 crop contaminants, a mean of 3.5 contaminant species and 1,250 seeds kg−1. Two species prohibited by the Alaska seed law were found: Canada thistle was found in a single crop sample, and quackgrass was found in two grass samples. There were no significant relationships between either seed type or supplier and either the number of contaminant species or number of seeds. Labels of 33% of crop samples and 8% of grass samples claimed 0.00% weed seeds, but low (0.007% by weight, 2 species) to high (1.18% by weight, 13 species) amounts of weed contaminants were found. Importation of crop seed is a large pathway for seed movement, causing significant propagule pressure and an increased likelihood of establishment by new invasive plant populations. Prevention of spread via this pathway would be enhanced by changes to seed laws, by greater regulatory enforcement, and by including on the label, the names of all weed and contaminant crop species found in the law-required samples. Consumers could then make decisions on whether to purchase seed based on the potentially invasive species that would be planted with the desired seed.

The extent and nature of spread of exotic plant species to and within Alaska by shipment of hay and straw was studied. The amounts of hay and straw imported into Alaska and the amounts and types of seed in imported and locally produced hay and straw was determined We purchased alfalfa hay, wheat straw, ryegrass straw, and timothy hay produced in Washington and Oregon (WA–OR) and locally produced straw and hay. The hay and straw were shaken over screens, and the remaining fines were mixed with sterile potting soil and incubated in the greenhouse. Forty-nine plant species were identified from hay and straw, nine of which are ranked as invasive in Alaska, including downy brome, foxtail barley, hare barley, narrowleaf hawksbeard, and quackgrass—a prohibited weed in Alaska. The number of seeds ranged from 0 to 6,205 seeds kg−1, with an average of 585 seeds kg−1, and the number of species ranged from 0 to 12, with an average of 4.2 species per bale. Crop seed comprised a large proportion of the germinated seeds in ryegrass straw, wheat straw, and timothy/brome hay (98, 78, and 62%, respectively), but was less prevalent (ranging from 0 to 38%) in the other three hay and straw crop types. Hay and straw from Alaska contained more total seeds and species than hay and straw from WA-OR, but the difference was not significant when only weed seed was used in the analysis. Alaska-grown timothy/brome hay contained significantly more total seed than alfalfa hay and wheat straw from WA–OR and Alaska-grown barley straw. The grower or distributor of the hay and straw also influenced the number of seeds and species among some crop types. Results of this study document that large numbers of alien plant species are transported by movements of hay and straw into and within Alaska.

Orange hawkweed is a perennial European plant that has colonized roadsides and grasslands in south-central and southeast Alaska. This plant is forming near-monotypic stands, reducing plant diversity, and decreasing pasture productivity. A replicated greenhouse study was conducted in 2006 and repeated in 2007 to determine the efficacy of six herbicides (aminopyralid, clopyralid, picloram, picloram + chlorsulfuron, picloram + metsulfuron, and triclopyr) for orange hawkweed control. Based on results of the greenhouse trials, replicated field studies were conducted at two sites each year in 2007 and 2008 with three rates each of aminopyralid and clopyralid to determine efficacy of orange hawkweed control and impacts on nontarget native vegetation. In the field, only aminopyralid at 105 g ae ha−1 (0.1 lb ae ac−1) and clopyralid at 420 g ae ha−1 controlled orange hawkweed consistently, with peak injury observed 1 yr after treatment. Control with clopyralid was slightly less than that provided by aminopyralid at all observation times, except at Homer, AK, in 2007, where there was a near-monotypic stand of orange hawkweed, and clopyralid did not remove all orange hawkweed plants. Aminopyralid controlled clover (Trifolium spp.), seacoast angelica (Angelica lucida), arctic daisy (Chrysanthemum arcticum), common hempnettle (Galeopsis tetrahit), and willow (Salix spp.) in the treated areas. Other plant species, such as grasses and some annual forbs, recovered or increased following control of the hawkweed. Clopyralid had less impact on nontarget species with most recovering the year after treatment. In a pasture system, where grasses are preferred to forbs and shrubs, aminopyralid has an advantage because it controls a broader array of forbs compared with clopyralid. In natural areas, where the desire to retain biodiversity and the aesthetics of multiple forb species mixed with grasses and willows is preferred, clopyralid will leave greater species diversity than aminopyralid.

White sweetclover is invading the Alaska glacial river floodplains and roadsides adjacent to natural areas, and control methods are needed. Chlorsulfuron, 2,4-DB, clopyralid, triclopyr, and 2,4-D controlled white sweetclover seedlings below recommended rates in the greenhouse. Biomass of established plants in the field was reduced by chlorsulfuron at recommended (17.6 g ai/ha), 1/2, and 1/4 rates and was reduced by triclopyr and 2,4-D at recommended rates (1,260 and 1,600 g ai/ha). Herbicides were more effective at reducing white sweetclover viable seed production in 2007 than in 2006. Only chlorsulfuron at 17.6 g ai/ha (recommended rate) eliminated seed production in both years. Flaming killed first-year plants, but some second-year plants resprouted and produced viable seed. Cutting at the 2.5 or 10 cm height did not control first-year plants because of regrowth, and second-year plant density and seed production was reduced by cutting at 2.5 cm but not by cutting at 10 cm.

To determine the extent and nature of container-grown plant soil as a pathway for introduction of exotic plant species to Alaska, soil from container-grown ornamentals was obtained from vendors and was incubated in the greenhouse. Fifty-four plant species were identified growing in containers or germinating from the soil, and included Canada thistle—a prohibited weed in Alaska—and nine other species listed as invasive in Alaska. The number of species and estimated seed bank were very low for soil from vegetable starts/herbs and herbaceous bedding plants (< 2 seedlings/L soil), but was greater for soil from containers containing woody plants, especially balled and burlapped ornamentals (20 seedlings/L soil). Container alien plant seed bank size was strongly related to type of soil. Potting (soil-less) soil contained 1.2 germinating seeds/L, soil-based soil 5.5 seeds/L, and mineral soil 18.7 seeds/L. Growers and vendors were variables that also influenced the size of the container seed bank, suggesting that weed management practiced during production and at the point of sale can greatly influence seed banks of ornamental containers.

In Alaska Conservation Reserve Program (CRP) lands, succession of fields planted with grass and clover to shrubs and small trees is resulting in program compliance problems related to ease of reconversion to crop lands. Standard practice for slowing this succession is mowing every 2 to 3 yr, which does not kill the woody vegetation. A field study was conducted at three sites over 2 yr to determine if 2,4-D (2.2 kg ae ha−1 2-ethylhexyl ester) or triclopyr (2.2 kg ae ha−1 butoxyethyl ester) applied broadcast or 2,4-D (2.2 kg ae ha−1 2,4-D dimethylamine salt) or triclopyr (1.7 kg ae ha−1 triclopyr triethylamine salt) applied with a Diamond Wet Blade™ mower (DWB) would result in longer shrub control compared to mowing. Mowing was conducted at both 15 and 45 cm above ground level and herbicides were applied with the DWB at three rates. Measurements 2 yr after treatment (YAT) confirmed that both herbicides reduced shrub cover about 50% compared to controls. Reduced rates of the herbicides applied with the DWB did not result in decreased shrub control. Grass cover was negatively correlated with shrub cover. Typically, mower height did not alter treatment effects. Treatments had little impact on forb cover and composition 2 YAT, with the exception of fireweed, which was generally reduced where herbicides were applied. Application of 2,4-D and triclopyr does not decrease the frequency of shrub control in CRP lands in Alaska. Use of 2,4-D and triclopyr with or without mowing resulted in no widespread improvement over the current practice of mowing to 15 cm every 2 to 3 yr.

A study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2 and 15 cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, and 19.7 yr later. Viability was determined by germination and tetrazolium tests. Seed viability data were fit to an exponential model, separately for each depth, and the likelihood-ratio test was used to determine whether seed-viability decline was affected by burial depth. Depth of burial had a significant effect on viability decline of prostrate knotweed, marsh yellowcress, bluejoint reedgrass, and wild oat. By 19.7 years after burial (YAB), all seeds of common hempnettle, quackgrass, wild oat, foxtail barley, and bluejoint reedgrass were dead. Seeds of 12 other species were still viable: corn spurry (0.1%), prostrate knotweed (0.3% at 2 cm, 0.8% at 15 cm), flixweed (0.5%), pineapple-weed (0.6%), shepherd's-purse (1.3%), wild buckwheat (1.5%), common chickweed (1.6%), rough cinquefoil (1.8%), common lambsquarters (3.0%), Pennsylvania smartweed (3.3%), marsh yellowcress (8.5% at 2 cm, 0.3% at 15 cm), and American dragonhead (62.2%). Seed dormancy at 19.7 YAB was very low for all species (< 4%) except for American dragonhead, common lambsquarters, Pennsylvania smartweed, and shepherd's-purse, which had seed dormancies of 100, 27, 25, and 38%, respectively. Seed longevity was not increased by cold, subarctic temperatures.

A 50-yr study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2- and 15-cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, 19.7, and 24.7 yr later. Viability was determined using germination and tetrazolium tests. By 24.7 yr after burial (YAB), no viable seeds were found for common hempnettle, flixweed, foxtail barley, quackgrass, and wild oat. Bluejoint reedgrass, which had no live seed 19.7 YAB, again had viability (1% at 15 cm) 24.7 YAB. Seeds of 11 other species were still viable: American dragonhead (52%), marsh yellowcress (11 and 3.0% at 2 and 15 cm respectively), common lambsquarters (2.8%), prostrate knotweed (2.8% at 15 cm), shepherd's-purse (2.8%), pineapple-weed (2.6%), rough cinquefoil (2.3%), Pennsylvania smartweed (1.1%), common chickweed (0.4%), wild buckwheat (0.3%), and corn spurry (0.1%). Seed dormancy 24.7 YAB was very low (< 10%) for all species except American dragonhead (99%), shepherd's-purse (40%), marsh yellowcress (23% at 2 cm), Pennsylvania smartweed (18%), and rough cinquefoil (14%). At the beginning of the study, declines in seed longevity were uniform between replicates, but variability between replicates increased over time for all species except American dragonhead, suggesting that some soil microsites are more favorable for seed survival and may be seedbank “safe sites.” Results of this study demonstrate that nonrandom seed mortality contributes to the spatial heterogeneity of seed populations in the soil seedbank.

Bird vetch is a perennial Eurasian plant which, unlike many exotic weed species, can invade low fertility areas that have not been disturbed. It also is common in pastures, woodland, and tall forb communities. Bird vetch is expanding along Alaskan roadsides, in urbanized areas, and in low density forests. A greenhouse study was conducted to determine efficacy of six herbicide treatments applied at reduced rates in 2005 and again in 2006 for bird vetch seedling control. Bird vetch seedlings were tolerant of reduced rates of chlorsulfuron and 2,4-DB; however, complete control was achieved with rates of clopyralid, dicamba plus diflufenzopyr, triclopyr, and 2,4-D that were a fourth to an eighth of the full registered rate. These results will be important for developing effective, low-cost methods for controlling bird vetch in Alaska, especially on the outer margins of infestations.