Steven S. Seefeldt

University of Alaska System · Agriculture and Horticulture

Clopyralid and dicamba are used in Alaska to control certain invasive and agricultural weed species; however they may have an extended soil half-life in interior Alaska resulting in carry-over injury in potatoes. Field studies at experiment stations in Delta Junction, Fairbanks, and Palmer, Alaska were established to determine the dose–response of...

We assessed the ability of climatic, environmental, and anthropogenic variables to predict areas of high-risk for plant invasion and consider the relative importance and contribution of these predictor variables by considering two spatial scales in a region of rapidly changing climate. We created predictive distribution models, using Maxent, for th...

Aminopyralid is used in Alaska to control certain invasive weed species; however it appears to have an extended soil half-life in interior Alaska resulting in carry-over injury in potatoes. Field studies at three experiment stations in Delta Junction, Fairbanks, and Palmer, Alaska were established to determine the dose–response of weeds and above a...

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 w...

Background/Question/Methods Species distributions are controlled by different factors at different spatial scales. We assessed the ability to create accurate predictive models for high-risk invasive plants species using climatic, environmental, and anthropogenic variables at different scales in a region of rapidly changing climate. We selected thre...

Dose—response analysis is widely used in biological sciences and has application to a variety of risk assessment, bioassay, and calibration problems. In weed science, dose—response methodologies have typically relied on least squares estimation under the assumptions of normal, homoscedastic, and independent errors. Advances in computational abiliti...

Dose–response analysis is widely used in biological sciences and has application to a variety of risk assessment, bioassay, and calibration problems. In weed science, dose–response methodologies have typically relied on least squares estimation under the assumptions of normal, homoscedastic, and independent errors. Advances in computational abiliti...

In summer, bands of sheep are grazed in western North American mountains. At night the sheep are concentrated into bedding areas. In the study area, each bedding area is only utilized by sheep for one night a year for 2 out of 3 years. Vegetation in the bedding areas was compared to vegetation outside these areas. Both perennial forb cover and tota...

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 herbici...

Dose-response estimation.

The use of triclopyr for the removal of woody and broad-leaf vegetation in right-of-ways and agricultural settings has been proposed for Alaska. Triclopyr concentrations in soil after application are of concern because residual herbicide may affect growth of subsequent vegetation. In order to measure triclopyr residues in soil and determine the amo...

Jointed goatgrass is an invasive winter annual grass weed that is a particular problem in the low to intermediate rainfall zones of the Pacific Northwest (PNW). For the most part, single-component research has been the focus of previous jointed goatgrass studies. In 1996, an integrated cropping systems study for the management of jointed goatgrass...

White sweetclover and narrowleaf hawksbeard are nonindigenous invasive plant species in Alaska that are rapidly spreading, including into areas that are otherwise free of nonindigenous plants. There has been concern that native moose could be dispersing germinable seed from these plants after ingestion. To address this concern, a study was conducte...

Although many land managers prohibit grazing for 2 years after a fire, little research has been conducted to determine the interaction of grazing with vegetation recovery after fire. In a study conducted in sagebrush steppe rangelands after a 2000 wildfire at the United States Sheep Experiment Station in Idaho, the influence of delay and season of...

Over 14 million hectares of erosion prone cropland in the United States has been converted into grasslands through the Conservation Reserve Program (CRP) administered by the United States Department of Agriculture, however, studies of the effects of CRP enrollment on plant communities and subsequent plant succession are largely lacking. In Delta Ju...

Remote sensing indices of burn area and fire severity have been developed and tested for forest ecosystems, but not sparsely vegetated, desert shrub-steppe in which large wildfires are a common occurrence and a major issue for land management. We compared the performance of remote sensing indices for detecting burn area and fire severity with exten...

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...

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 determi...

Any plant not sown from seed is often labeled a weed in improved pastures of New Zealand. Most improved pastures are a mix of perennial ryegrass and white clover but generally are infested with broadleaf weeds. Changes in forage production due to individual weeds were determined using measurements of perennial ryegrass and white clover before and a...

In the semi-arid steppe rangelands of Central Turkey, Festuca valesiaca and Thymus sipyleus ssp rosulans have become the dominant species on degraded pastures. We hypothesized that decreases in species richness and abundance are correlated with increasing prevalence of these two species. Therefore, our objectives were to determine whether there are...

Fires are common in rangelands, and after a century of suppression, the potential exists for fires to burn with high intensity and severity. In addition, the abil-ity of fires to affect long-term changes in rangelands is substantial; therefore, the assessment of fire severity following a burn is critical. These assessments are typi-cally conducted...

Wildland fires are common in rangelands worldwide. The potential for high severity fires to affect long- term changes in rangelands is considerable, and for this reason assessing fire severity shortly after the fire is critical. Such assessments are typically carried out following Burned Area Emergency Response teams or similar protocols. These dat...

In the last 50 years, rangelands in the Central Anatolian Region of Turkey have been converted to cropping lands, which has negatively accelerated vegetation change, resulting in overgrazing and poor condition and productivity. In these steppe rangelands, to develop a rational basis for making restoration and management decisions, the vegetation st...

Sheep and lamb production is an important industry in Idaho, with summer sheep grazing in the mountains a common practice. Sheep are concentrated in bedding areas at night leading to concentrated grazing and manure and urine accumulation in these areas. To address the effects of bedding on soil nutrient status, we monitored 16 bedding areas in the...

In the last 50 years, rangelands in the Central Anatolian Region of Turkey have been converted to cropping lands, which has negatively accelerated vegetation change, resulting in overgrazing and poor condition and productivity. In these steppe rangelands, to develop a rational basis for making restoration and management decisions, the vegetation st...

The potential for high severity fires to affect changes in rangelands is considerable, and for this reason, assessing fire severity is critical. We explored fire severity modeling in rangelands by applying post-fire field observations to Satellite Pour l'Observation de la Terre 5 (SPOT 5) imagery using Classification Tree Analysis (CTA) techniques...

Question: What is the impact of prescribed fires on the cover and composition of vegetation in Artemisia tridentata ssp. vaseyana steppe? Location: United States Department of Agriculture, Agricultural Research Service, United States Sheep Experiment Station, eastern Idaho (44°14′44′’ N, 112°12′47′’ W). Methods: Multiple prescribed fires were lit i...

Field studies were conducted in Idaho from 2002 to 2004 to determine whether summer grazing of sheep for 1 or 2 years before an autumn application of imazapic would enhance control of Euphorbia esula. E. esula, a perennial plant native to parts of Europe and Asia, has invaded the Great Plains and Rocky Mountains after its introduction into North Am...

Over the last fifty years, almost half of the steppe rangeland in the Central Anatolian Region of Turkey (CAR) has been converted to cropland without an equivalent reduction in grazing animals. This shift has led to heavy grazing pressure on rangeland vegetation. A study was initiated in June 2003 using 6 multiscale Modified-Whittaker plots to dete...

Methods that are more cost-effective and objective are needed to detect important vegetation change within acceptable error rates. The objective of this research was to compare visual estimation to three new methods for determining vegetation cover in the sagebrush steppe. Fourteen management units at the US Sheep Experiment Station were identified...

A dense mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana Rydb Beetle) canopy suppresses understory vegetation. Rambouillet ewes with high and low dietary preferences for mountain big sagebrush were tested for their ability to reduce the cover of dense stands of sagebrush. Eighty ewes with high and low preferences for mountain big sa...

A dense mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb] Beetle) canopy suppresses understory vegetation. Rambouillet ewes with high and low dietary preferences for mountain big sagebrush were tested for their ability to reduce the cover of dense stands of sagebrush. Eighty ewes with high and low preferences for mountain big...

In July 2000, a 490-ha wildfire burned a portion of a long-term grazing study that had been established in 1924 at the US Sheep Experiment Station north of Dubois, Idaho, USA. Earlier vegetation measurements in this tall threetip sagebrush (Artemisia tripartita spp. tripartita) bunchgrass plant community documented significant changes in vegetatio...

A field and an outdoor tray experiment were conducted to determine whether weed control benefits of high sowing rates of perennial ryegrass (Lolium perenne) continue into the second year after sowing. Seeds of Scotch thistle (Cirsium vulgare), nodding thistle (Carduus nutans) and hedge mustard (Sisymbrium officinale) were sown into perennial ryegra...

The impact of grazing pasture to different heights on the development of Californian thistle (Cirsium arvense) was simulated over two years in container trials Californian thistle field densities were simulated by transplanting seedlings into perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) that had been sown at 20 and 5 kg/h...

In eastern Washington, spring wheat cultivars that germinate and grow fast at low temperatures will provide the crop with a competitive advantage over spring emerging weeds in commercial production fields compared to cultivars that germinate and grow more slowly. The objective of this research was to develop a protocol to identify spring wheat cult...

The effect of the density of perennial ryegrass (Lolium perenne) swards on the emergence of ragwort (Senecio jacobaea) was investigated in the field and in trays Ragwort seeds were sown into established perennial ryegrass and white clover (Trifolium repens) swards and the seedlings were mapped at intervals to aid in identification of new seedlings...

Three models that empirically predict crop yield from crop and weed density were evaluated for their fit to 30 data sets from multistate, multiyear winter wheat-jointed goatgrass interference experiments. The purpose of the evaluation was to identify which model would generally perform best for the prediction of yield (damage function) in a bioecon...

Research was conducted to determine the effect of perennial ryegrass (Lolium perenne) sowing density on weed growth and development In glasshouse and field experiments perennial ryegrass was sown at rates of 0 5 10 20 40 and 80 kg/ha with 5 kg/ha of white clover (Trifolium repens) With increasing seeding density perennial ryegrass enhanced its comp...

Crop yield loss-weed density relationships critically influence calculation of economic thresholds and the resulting management recommendations made by a bioeconomic model. To examine site-to-site and year-to-year variation in winter Triticum aestivum L. (winter wheat)-Aegilops cylindrica Host. (jointed goargrass) interference relationships, the re...

Neat isolines of 'Nugaines' winter Triticum aestivum that differed in height were planted with and without Aegilops cylindrica to determine the effect of plant height on competition against A. cylindrica. The isolines had either reduced height gene Rht1, Rht2, Rht1 plus Rht2, or neither Rht genes and averaged 79, 77, 51, and 101 cm tall, respective...

A 1984-1985 and 1988-1989 field study near Pullman, WA, evaluated the effect of two winter wheat planting geometries on the growth of wheat and competition against jointed goatgrass. Treatments included paired and constant row planting geometries of wheat and locations of jointed goatgrass within each geometry. No planting geometry by weed location...

Our objective was to identify traits in winter wheat important to competitiveness against jointed goatgrass, measured as increased wheat yields and reduced jointed goatgrass seed production. Jointed goatgrass is an important winter annual grass weed that cannot be controlled selectively in winter wheat. Seven cultivars of soft white winter wheat we...

Imazamox-resistant hybrids resulted from a cross between jointed goatgrass and an imazamox-resistant wheat (cv. FS-4 IR wheat). Two imazamox-resistant hybrids were discovered in a research plot where FS-4 IR wheat seed had been replanted from the harvest of an imazamox efficacy study conducted the year before at a different location. These hybrid p...

Dose-response studies are an important tool in weed science. The use of such studies has become especially prevalent following the widespread development of herbicide resistant weeds. In the past, analyses of dose-response studies have utilized various types of transformations and equations which can be validated with several statistical techniques...

A long-standing hypothesis for the invasive success of exotic species following disturbance is that disturbances promote invasions by increasing resource availability to the selective advantage of invasive species. Consistent with this hypothesis, efficiency of resource use is predicted to be less in invasive compared to native species. Furthermore...

An understanding of why infestations occur helps land managers target causes and not just symptoms of invasions. Syndromes, which are recurring sets of symptoms that are characteristic of a particular disorder or disease, help link basic and generalizable science with the specific treatment needs of individuals in clinical practice, or sites in lan...

Computer-produced typeface. Thesis (Ph. D.)--Washington State University, 1995. Includes bibliographical references (leaves 122-139).