Jed B. Colquhoun

Identification of glyphosate-resistant Italian ryegrass (Lolium multiflorum) in Oregon

Abstract A suspected glyphosate-resistant Italian ryegrass biotype was collected from a filbert orchard near Portland, OR, where glyphosate was applied multiple times per year for about 15 yr. Greenhouse studies were conducted to determine if this biotype was glyphosate resistant. The plants were sprayed with glyphosate (0.01 to 3.37 kg ae ha−1) 14 d after planting and shoot biomass was determined 3 wk after herbicide treatment. Based on the dose–response experiments conducted in the greenhouse, the suspected Italian ryegrass biotype was approximately fivefold more resistant to glyphosate than the susceptible biotype. Plants from both susceptible and resistant biotypes were treated with glyphosate (0.42 and 0.84 kg ha−1) and shikimic acid was extracted 12, 24, 48, and 96 h after treatment. The susceptible biotype accumulated between three and five times more shikimic acid than did the resistant biotype. Leaf segments from both susceptible and resistant biotypes were incubated with different glyphosate concentrations (0.5 to 3000 μM) for 14 h under continuous light. Shikimic acid was extracted from each leaf segment and quantified. At a concentration up to 100 μM, leaf segments from the susceptible biotype accumulated more shikimic acid than leaf segments from the resistant biotype. The epsps gene was amplified and sequenced in both susceptible and resistant biotypes; however, no amino acid change was found in the resistant biotype. The level of resistance in this biotype is similar to that reported for a glyphosate-resistant Italian ryegrass biotype from Chile. Nomenclature: Glyphosate; Italian ryegrass, Lolium multiflorum Lam. LOLMU; filbert, Corylus avellana L.

A predictive degree-days model for small broomrape (Orobanche minor) parasitism in red clover in Oregon

Abstract Weeds of the genus Orobanche parasitize many dicotyledonous species, causing severe damage to vegetable and field crops worldwide. In Oregon, the number of red clover fields contaminated with small broomrape has increased in recent years. Small broomrape parasitism in red clover is temperature related. In this study, the temperature-dependent relationship was developed into a predictive model based on growing degree-days (GDD) for small broomrape parasitism in red clover. The model was developed in greenhouse studies and validated in the field during three growing seasons. A strong relationship between GDD and parasite size allowed for the creation of a simple predictive model for tubercle number based on GDD. The proposed model is based on a temperature range realistic to western Oregon climatic conditions and predicts lag, log, and maximum phases for four parasitism sizes in relation to GDD. Small broomrape parasitism in red clover began at about 400 GDD, but red clover biomass accumulation was not affected by parasitism before 1,200 GDD. Small broomrape flower stalk emergence began at about 1,100 GDD. Field studies validated that GDD could be a predictive parameter for small broomrape parasitism and could be used to time detection surveys and herbicide applications. Nomenclature: Small broomrape, Orobanche minor J. E. Smith. ORAMI; red clover, Trifolium pratense L. TRFPR.

The relationship between temperature and small broomrape (Orobanche minor) parasitism in red clover (Trifolium pratense)

Abstract The root-parasitic broomrape species cause severe damage to field and vegetable crops worldwide. This study evaluated the relationship between small broomrape development and temperature with red clover as a host plant. Red clover plants were grown in soil artificially infested with small broomrape seed in temperature-controlled growth chambers. Parasite development was quantified at 48 different accumulated growing degree days (GDD). Small broomrape parasitism and temperature were strongly related. Small broomrape tubercle initiation was delayed by low temperature. Tubercle development initiated at about 750 GDD and peaked at about 1,100 GDD. Small broomrape biomass accumulation correlated with the increase in tubercle number over time. Parasitism stages were divided into lag, log, and maximum phases that were strongly related to GDD. Development of a predictive system for parasitism growth stage is needed to allow precise herbicide application for effective control before small broomrape shoot emergence. Nomenclature: Small broomrape, Orobanche minor Sm. ORAMI; red clover, Trifolium pratense L. TRFPR.

Small broomrape (Orobanche minor) germination and early development in response to plant species

Abstract Small broomrape, a holoparasitic weed, was recently introduced to the Pacific Northwest and contaminates a limited number of red clover fields in Oregon. Greenhouse and field studies were conducted to evaluate small broomrape response to common crop and weed species in the Pacific Northwest, and to evaluate a quick-screening method for plant species response to the parasite. In greenhouse studies, plants were grown in a hydroponic polyethylene bag system to allow for continuous visibility of their roots and monitoring of small broomrape seed germination and tubercle development. Results of the greenhouse study were validated in a field contaminated with small broomrape. In the greenhouse polyethylene bag study, small broomrape germinated and tubercles developed on alfalfa, arrowleaf clover, carrot, celery, crimson clover, lettuce, prickly lettuce, red clover, spotted catsear, subterranean clover, white clover, and wild carrot. Small broomrape germinated but did not develop tubercles when grown with barley, birdsfoot trefoil, common vetch, creeping bentgrass, cucumber, field corn, red fescue, flax, Italian ryegrass, nasturtium, oats, orchardgrass, perennial ryegrass, snap bean, sugar pea, sunflower, sweet corn, tall fescue, tomato, and wheat. In the field study, tubercles developed on alfalfa, arrowleaf clover, common vetch, crimson clover, red clover, subterranean clover, and white clover, but small broomrape flower stalks did not emerge in arrowleaf clover or crimson clover. Common vetch was a host for small broomrape in the field study but not in the hydroponic polyethylene bag system, thus, caution is warranted in using the quick screening method to elucidate potential small broomrape host species. Nomenclature: Curly dock, Rumex crispus L. RUMCR; prickly lettuce, Lactuca serriola L. LACSE; spotted catsear, Hypochaeris radicata L. HYPRA; wild carrot, Daucus carota L. DAUCA; alfalfa, Medicago sativa L. MEDSA; arrowleaf clover, Trifolium vesciculosum Savi. TRFVE; barley, Hordeum vulgare L. HORVX; birdsfoot trefoil, Lotus corniculatus L. LOTCO; carrot, Daucus carota L. DAUCS; celery, Apium graveolens L. AOUGD; common vetch, Vicia sativa L. VICSA; creeping bentgrass, Agrostis stolonifera L. AGSTE; crimson clover, Trifolium incarnatum L. TRFIN; cucumber, Cucumis sativus L. CUMSA; field corn, Zea mays L. ZEAMA; flax, Linum usitatissimum L. LIUUT; Italian ryegrass, Lolium multiflorum Lam. LOLMU; lettuce, Lactuca sativa L. LACSA; nasturtium, Tropaeolum majus L. TOPMA; oats, Avena sativa L. AVESA; orchardgrass, Dactylis glomerata L. DACGL; perennial ryegrass, Lolium perenne L. LOLPE; red clover, Trifolium pratense L. TRFPR; red fescue, Festuca rubra L. FESRU; small broomrape, Orobanche minor Sm. ORAMI; snap bean, Phaseolus vulgaris L. PHSVN; subterranean clover, Trifolium subterraneum L. TRFSU; sugar pea, Pisium sativum L. PIBST; sunflower, Helianthus annuus L. HELAN; sweet corn, Zea mays L. ZEAMS; tall fescue, Festuca arundinaceae Schreb. FESAR; tomato, Lycopersicon esculentum Mill. LYPES; wheat, Triticum aestivum L. TRZAW; white clover, Trifolium repens L. TRFRE.

Imazamox application timing for small broomrape (Orobanche minor) control in red clover

Abstract Broomrapes (Orobanche spp.) are chlorophyll-lacking root parasites of many dicotyledonous species and cause severe damage to vegetable and field crops from several botanic families such as Fabaceae, Solanaceae, Compositae, and Umbelliferae. In Oregon, small broomrape has been identified as a parasite of red clover. In Oregon field studies, small broomrape control was excellent when imazamox was applied postemergence to red clover but preemergence to small broomrape. Temperature is one of the main factors that affect broomrape development. The objective of this study was to optimize small broomrape chemical control in red clover based on growing degree days (GDD). The study was conducted in controlled temperature conditions. Red clover plants were grown in soil artificially infested with small broomrape seeds. Imazamox was applied at 800, 1,000, 1,200, and 1,400 GDD. There was no injury to red clover from any imazamox treatment at any of the application timings. Small broomrape shoot emergence was reduced where imazamox was applied compared to the untreated control. Early imazamox applications reduced small broomrape biomass more than later applications. Control was greatest when imazamox was applied at 20 g ai ha−1 at 1,000 GDD. This application controlled small broomrape for 800 GDD after initial treatment. However, season-long control would require an additional treatment. This model predicts the optimal timing and rate of imazamox application for small broomrape control in red clover. Nomenclature: Imazamox; small broomrape, Orobanche minor J. E. Smith ORAMI; red clover, Trifolium pratense L. TRFPR.

Measuring farm sustainability using data envelope analysis with principal components: The case of Wisconsin cranberry

Measuring farm sustainability performance is a crucial component for improving agricultural sustainability. While extensive assessments and indicators exist that reflect the different facets of agricultural sustainability, because of the relatively large number of measures and interactions among them, a composite indicator that integrates and aggregates over all variables is particularly useful. This paper describes and empirically evaluates a method for constructing a composite sustainability indicator that individually scores and ranks farm sustainability performance. The method first uses non-negative polychoric principal component analysis to reduce the number of variables, to remove correlation among variables and to transform categorical variables to continuous variables. Next the method applies common-weight data envelope analysis to these principal components to individually score each farm. The method solves weights endogenously and allows identifying important practices in sustainability evaluation. An empirical application to Wisconsin cranberry farms finds heterogeneity in sustainability practice adoption, implying that some farms could adopt relevant practices to improve the overall sustainability performance of the industry.

Postemergence Small Broomrape (Orobanche minor) Control in Red Clover

Small broomrape is an annual, parasitic weed that was discovered recently in Oregons red clover seed production system. Field experiments were conducted in 2002 and 2003 at two locations to evaluate 10 herbicide treatments applied after small broomrape emergence in red clover. Bentazon, bromoxynil, glyphosate, imazamox, imazamox plus bentazon, imazethapyr, MCPA, and pendimethalin were evaluated. Small broomrape density, small broomrape seed viability after treatment, and clover injury and seed yield were quantified. Small broomrape control with imazamox, glyphosate, and imazamox plus bentazon treatments was greater than the nontreated check in both years. However, imazamox and imazamox plus bentazon treatments were the only herbicide treatments that consistently exhibited a high level of crop safety, reduced small broomrape density, and did not reduce red clover yield. Herbicide treatments did not prevent production of viable small broomrape seeds. Future research is needed to develop control options that will prevent red clover yield loss and viable small broomrape seed production when applied before small broomrape emergence. Nomenclature: Bentazon; bromoxynil; glyphosate; imazamox; imazethapyr; MCPA; pendimethalin; small broomrape, Orobanche minor Sm. #3 ORAMI; red clover, Trifolium pratense L. # TRFRE. Additional index words: Parasitic weed. Abbreviations: DAT, days after treatment.

Herbicide Placement Site Affects Small Broomrape (Orobanche minor) Control in Red Clover

Small broomrape is an annual holoparasitic weed that was recently discovered in red clover production fields in Oregon. Imidazolinone herbicides such as imazamox control small broomrape; however, the mechanism of uptake by the parasite is largely unknown. Studies were conducted to determine the imazamox route of uptake by small broomrape in red clover, and to determine the potential for imazamox to be exuded from red clover and the subsequent effect on small broomrape. Small broomrape control was best at 90% when imazamox was foliar-applied, and worst at 42% or less when imazamox was soil-applied. The presence of activated charcoal to adsorb imazamox at the soil surface did not affect efficacy of broadcast foliar treatment. Small broomrape control was also evaluated when a foliar-treated red clover plant was grown in the same pot as a nontreated, parasitized red clover plant that was bagged during herbicide application. Activated charcoal was spread on the soil surface to adsorb imazamox, thus limiting herbicide uptake routes to the foliage of one of two red clover plants in the pot. Small broomrape attachment decreased on nontreated red clover when the other red clover plant in the pot was treated, suggesting roots exuded the herbicide or an active metabolite. Nomenclature: Imazamox; small broomrape, Orobanche minor J. E. Smith. # ORAMI; red clover, Trifolium pratense L. # TRFPR. Additional index words: Parasitic plant, imazamox. Abbreviations: DAT, days after treatment.

Ability of Potato Cultivars to Tolerate and Suppress Weeds

Abstract Potato producers rely heavily on herbicides for the majority of weed control. However, recent occurrences of herbicide-resistant weed populations and the lack of new herbicide registrations have stimulated interest in alternative strategies. The choice of potato cultivars that can suppress or tolerate weed competition could be a component of an integrated weed management system to reduce reliance on herbicides. The competitive ability of 10 potato cultivars—‘Atlantic’, ‘Bannock Russet’, ‘Dark Red Norland’, ‘Goldrush’, ‘Rodeo’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Snowden’, ‘Superior’, and ‘Villetta Rose’—was evaluated in 2006 and 2007 in Hancock, WI. Weed competition treatments included (1) weedy throughout the season, (2) weed-free from emergence to 4 wk after emergence (WAE) by hand-weeding, and (3) weed-free by hand-weeding for the entire season. Potato cultivars did not differ in ability to reduce weed biomass. Early-season time of potato emergence and canopy closure, as well as weed competition treatments, were strongly related to potato tuber yield. In general, Bannock Russet yield relative to weed-free controls of the same cultivar was less than that of most other cultivars. Overall, Atlantic, Russet Burbank, Snowden, and Superior yields (relative to weed-free control yields) usually were greater than the yields of other cultivars under weedy conditions. Although the ability to suppress weeds was similar among cultivars, differences in yield among cultivars grown in the presence of weeds suggest differential tolerances of weed competition. Nomenclature: Potato, Solanum tuberosum ‘Atlantic’, ‘Bannock Russet’, ‘Dark Red Norland’, ‘Goldrush’, ‘Rodeo’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Snowden’, ‘Superior’, ‘Villetta Rose’.

Effect of Small Broomrape (Orobanche Minor) on Red Clover Growth and Dry Matter Partitioning

Abstract Small broomrape is a parasite of several broadleaf plant species. Consequences of small broomrape infestation in host cropping systems include seed contamination, reduction in crop seed yield, and host plant death. The effect of small broomrape parasitism on the biomass partitioning of its primary host, red clover, has not been documented. Greenhouse experiments were conducted to determine the relationship between small broomrape and red clover biomass accumulation. Total biomass of parasitized red clover plants was 15 to 51% less than nonparasitized red clover plants. Small broomrape parasitism reduced the amount of dry matter allocated to red clover inflorescences by 50 to 80%. Small broomrape dry matter accumulation was strongly related to total red clover–small broomrape dry matter accumulation. Small broomrape attachment number per red clover plant was a poor indicator of relative small broomrape dry weight accumulation. The results of this study indicated that small broomrape accumulated resources from red clover at the greatest expense to the economically important reproductive tissues. Nomenclature: Small broomrape, Orobanche minor Sm. ORAMI; red clover, Trifolium pratense L. TRFPR