Jeffery S. Conn

Seed viability and dormancy of 17 weed species after 19.7 years of burial in Alaska

Abstract 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%), shepherds-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 shepherds-purse, which had seed dormancies of 100, 27, 25, and 38%, respectively. Seed longevity was not increased by cold, subarctic temperatures. Nomenclature:  American dragonhead, Dracocephalum parviflorum Nutt. DRAPA; bluejoint reedgrass, Calamagrostis canadensis (Michx.) Beauv. CLMCD; common chickweed, Stellaria media (L.) Vill. STEME; Common hempnettle, Galeopsis tetrahit L. GAETE; common lambsquarters, Chenopodium album L. CHEAL; corn spurry, Spergula arvensis L. SPRAR; flixweed, Descurainia sophia (L.) Webb ex Prantl DESSO; foxtail barley, Hordeum jubatum L. HORJU; marsh yellowcress, Rorippa islandica (Oeder) Borbas RORIS; Pennsylvania smartweed, Polygonum pensylvanicum L. POLPY; pineapple-weed, Matricaria matricarioides (Less.) C.L. Porter MATMT; prostrate knotweed, Polygonum aviculare L. POLAV; quackgrass, Elytrigia repens (L.) Nevski AGRRE; rough cinquefoil, Potentilla norvegica L. PTLNO; shepherds-purse, Capsella bursa-pastoris (L.) Medicus CAPBP; wild buckwheat, Polygonum convolvulus L. POLCO; wild oat, Avena fatua L. AVEFA.

Characterizing Pathways of Invasive Plant Spread to Alaska: II. Propagules from Imported Hay and Straw

Abstract 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. Nomenclature: Alfalfa, Medicago sativa L.; downy brome, Bromus tectorum L. foxtail barley, Hordeum jubatum L. hare barley, Hordeum murinum L. ssp. leporinum (Link) Arcang; narrowleaf hawksbeard, Crepis tectorum L. quackgrass, Elymus repens (L.) Gould; ryegrass, Lolium spp.; timothy, Phleum pratense L.; wheat, Triticum aestivum L

Effects of tillage and straw management on Alaskan weed vegetation: a study on newly cleared land

Conn, J.S., 1987. Effects of tillage and straw management on Alaskan weed vegetation: a study on newly cleared land. Soil Tillage Res., 9: 275-285. The effects of tillage and straw management in a continuous spring barley system were studied during 1983-1985 on land near Delta Junction, Alaska, that had just been cleared for agricultural production. This research was a part of a multidisciplinary approach to design agricultural systems to minimize soil erosion on interior Alaskan agricultural land. Total weed ground cover and cover of native grasses such as bluejoint reedgrass (Calamagrostis canadensis (Michx) Nutt.) and native broadleaves was highest in no-till plots and was lowest in plots that were disked twice each year. Total weed ground cover increased during 1983-1985. Ground cover of native grasses was greater when stubble and straw residues were left on the soil surface than when the residues and stubble were removed. Greater snow cover where stubble is left may help to prevent freezing injury to the native grasses.

Control of orange hawkweed (Hieracium aurantiacum) in southern Alaska.

Abstract 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. Nomenclature: Aminopyralid; chlorsulfuron; clopyralid; metsulfuron; picloram; triclopyr; Orange hawkweed, Hieracium aurantiacum L. HIEAU; arctic daisy, Chrysanthemum arcticum L. CHYAR; clover, Trifolium spp.; common hempnettle, Galeopsis tetrahit L. GAETE; seacoast angelica, Angelica lucida L. ANLU; willow, Salix spp Interpretive Summary: Land managers are often faced with the task of selecting a weed control treatment from among a wide variety of options. Frequently there are people with a wide variety of concerns, opinions, and ideas that will want to question or even legally challenge the mangers decision. Orange hawkweed is a nonindigenous, invasive plant species that is spreading rapidly in Alaska, and there are few options for its control. Chemical control methods for orange hawkweed have not been studied in Alaska. In addition, there are concerns about impacts on native plant species and hopes that reduced rates of herbicides will result in acceptable control with minimal impacts on other plant species. The results of this research indicate that higher rates of both aminopyralid and clopyralid are needed to effectively control orange hawkweed. In a pasture system, where grasses are preferred to forbs and shrubs, aminopyralid has an advantage because it will control many other species compared with clopyralid, and there will be an increase in grass productivity. In a field, where the aesthetics of multiple forb species mixed with grass and willows is preferred, clopyralid will have a reduced effect on many more of these species than will aminopyralid.

Variation in Seed Viability and Dormancy of 17 Weed Species after 24.7 Years of Burial: The Concept of Buried Seed Safe Sites

Abstract 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), shepherds-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%), shepherds-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. Nomenclature: American dragonhead, Dracocephalum parviflorum Nutt. DRAPA; bluejoint reedgrass, Calamagrostis canadensis (Michx.) Beauv. CLMCD; common chickweed, Stellaria media (L.) Vill. STEME; common hempnettle, Galeopsis tetrahit L. GAETE; common lambsquarters, Chenopodium album L. CHEAL; corn spurry, Spergula arvensis L. SPRAR; flixweed, Descurainia sophia (L.) Webb. ex Prantl DESSO; foxtail barley, Hordeum jubatum L. HORJU; marsh yellowcress, Rorippa palustris (L.) Bess. RORIS (in previous manuscripts called Rorippa islandica (Oeder) Borbas); Pennsylvania smartweed, Polygonum pensylvanicum L. POLPY; pineapple-weed, Matricaria discoidea DC. MATMT (in previous manuscripts called Matricaria matricariodes (Less.) C.L. Porter); prostrate knotweed, Polygonum aviculare L. POLAV; quackgrass, Elymus repens (L.) Gould AGRRE (in previous manuscripts called Elytrigia repens (L.) Nevski); rough cinquefoil, Potentilla norvegica L. PTLNO; shepherds-purse, Capsella bursa-pastoris (L.) Medik. CAPBP; wild buckwheat, Polygonum convolvulus L. POLCO; wild oat, Avena fatua L. AVEFA.

Effects of tillage and cropping sequence on Alaskan weed vegetation: Studies on land under cultivation for eleven years

Abstract Soil erosion is potentially a serious problem in Alaskan agricultural land located near Delta Junction, Alaska. The effects of tillage and cropping sequence on weed species composition and cover were studied from 1980 to 1982 on land near Delta Junction, Alaska, that had been in cultivation for 11 years. Ground cover of perennial grasses, foxtail barley ( Hordeum jubatum L.) and quackgrass ( Agropyron repens (L.) Beauv.), increased when tillage was reduced to less than two spring disking operations. Greater cover by perennial weeds occurred under no-till than under tilled treatments. Only a minimal amount of tillage (a single disking in the spring) was required to reduce total weed cover by > 50%. Total weed cover increased from 1981 to 1982 on plots receiving less than two diskings per year. Perennial grasses contributed more cover when spring barley ( Hordeum vulgare L.) rather than rapeseed ( Brassica campestris L.) was grown. The ground cover of perennial grass was greatest when barley was grown continuously rather than in rotation with rapeseed. Neither paraquat nor glyphosate adequately controlled introduced perennial grasses when barley was grown without rotation and without tillage. The short Alaskan growing season makes it difficult to control perennial grasses effectively with non-selective herbicides during the cropping year.

Invasive White Sweetclover (Melilotus officinalis) Control with Herbicides, Cutting, and Flaming

Abstract 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. Nomenclature: Chlorsulfuron; clopyralid; 2,4-D; 2,4-DB; dicamba; triclopyr; white sweetclover, Melilotus officinalis (L.) Lam.

Response of Seedling Bird Vetch (Vicia Cracca) to Six Herbicides

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. Nomenclature: Chlorsulfuron, clopyralid, dicamba, diflufenzopyr, triclopyr, 2,4-D, 2,4-DB, bird vetch, Vicia cracca L. VICCR

Pathways of Invasive Plant Spread to Alaska: III. Contaminants in Crop and Grass Seed

Abstract 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. Nomenclature: Canada thistle, Cirsium arvense (L.) Scop.; quackgrass, Elymus repens (L.) Gould. Management Implications: Seeds of invasive and other nonnative plants disperse to new areas via numerous pathways. Study of these pathways helps to focus limited budgets on prevention and early detection. This study examined the pathway of seed contaminants traveling to Alaska via imported crop and grass seed. Crop and grass seed were purchased from 13 retail seed outlets in Alaska and included 14 seed suppliers. Eighteen crop samples and 100 grass seed samples were collected and sampled using federally mandated protocols. Seed samples were analyzed for crop and weed contaminants using an approved laboratory. A total of 95 weed and 36 contaminant crop taxa were found. The average number of contaminant taxa was 6.4 for crop seed and 3.5 for grass seed. The average number of contaminant seed per kilogram of seed was 3,844 for crop seed and 1,250 for grass seed. Two species prohibited from transport or sale in Alaska were found in the samples: Canada thistle was found in a single crop sample, whereas quackgrass was found in two grass samples. Seed labels of 33% of crop seed samples and 8% of grass seed samples claimed to have 0.00% weed seeds yet contained numerous weed species. Six percent of crop samples and 8% of grass samples did not contain crop or weed contaminants, showing that it is possible to produce clean seed. Statistical analysis showed no differences between seed suppliers or crop species in the number of contaminant taxa or amounts of contaminant seed. Importation of seed into Alaska is a large pathway for movement of nonnative plants. Contaminant seed using this pathway are likely to establish because they are planted under enhanced conditions for survival with the crop seed. Prevention of spread via this pathway would be aided by revising seed laws, increasing regulatory enforcement, and including on the label the names of all weed and crop species found by the seed testing laboratory. Consumers could make a decision on whether to purchase seed based on the potentially invasive species that would be planted along with desired seed.

Shrub Control in Conservation Reserve Program Lands in Interior Alaska

Abstract 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. Nomenclature: 2,4-D; triclopyr; fireweed, Chamerion angustifolium (L.) Holub ssp angustifolium. Resumen En tierras del Programa de Reservas para la Conservación (CRP) de Alaska, la sucesión de campos sembrados con zacate y trébol a arbustos y árboles pequeños está resultando en problemas para el cumplimiento del programa en relación con la facilidad de reconversión a tierras agrícolas. La práctica estándar para retrasar esta sucesión es la chapia cada 2 a 3 años, la cual no mata la vegetación leñosa. Se realizó un estudio de campo en tres sitios durante 2 años para determinar si 2,4-D (2.2 kg ae ha−1 2-ethylhexyl ester) o triclopyr (2.2 kg ae ha−1 butoxyethyl ester) aplicados con aspersión generalizada o 2,4-D (2.2 kg ae ha−1 2,4-D sal dimethylamine) o triclopyr (1,7 kg ae ha−1 triclopyr sal triethylamine) aplicados con una chapeadora Damon Wet Blade TM (DWB) resultarían en un control más duradero de arbustos en comparación con la chapia. Se chapeó a 15 y 45 cm sobre la superficie del suelo y los herbicidas se aplicaron con el DWB a tres dosis. Mediciones 2 años después del tratamiento (YAT) confirmaron que ambos herbicidas redujeron la cobertura de arbustos en cerca de 50% en comparación con los testigos. Dosis reducidas de los herbicidas aplicados con DWB no resultaron en reducciones en el control de arbustos. La cobertura de zacates estuvo negativamente correlacionada con la cobertura de arbustos. Típicamente, la altura de la chapeadora no afectó el efecto de los tratamientos. Los tratamientos tuvieron un impacto menor en la cobertura y composición de plantas herbáceas de hoja ancha a 2 YAT, con la excepción de Chamerion angustifolium, la cual fue generalmente reducida cuando se aplicó herbicidas. La aplicación de 2,4-D y triclopyr no reduce la frecuencia de control de arbustos en tierras del CRP en Alaska. El uso de 2,4-D y triclopyr con o sin chapia no resultó en una mejora en comparación con la práctica actual de chapear a 15 cm cada 2 ó 3 años.