Donald C. Thill

Detecting Spotted Knapweed (Centaurea maculosa) with Hyperspectral Remote Sensing Technology1

Failure to detect noxious weeds with current survey methods prevents their control and has contributed to their ability to establish and spread in remote range and forest sites. Techniques used in remote sensing can classify plant occurrence on maps, offering a method for surveying invasive species in remote locations and across extensive areas. An imaging hyperspectral spectrometer recorded images on July 19, 1998 in Farragut State Park near Bayview, ID, in the reflected solar region of the electromagnetic spectrum ranging from 440 to 2,543 nm to detect spotted knapweed. The sensor records 128 spectral bands in 12- to 16-nm intervals at a spatial resolution of 5 m. A spectral angle mapper (SAM) algorithm was used to classify the data. Infestations in Idaho with 70 to 100% spotted knapweed cover that were 0.1 ha were detected regardless of the classification angle. However, narrow angles (2 to 8°) did not completely define the extent of the infestation, and the widest angle tested (20°) falsely classified some areas as infested. The overall image error for all classes was lowest (3%) when SAM angles ranged from 10 to 11°. Specific errors for the spotted knapweed class for the 10 to 11° angles showed that omissional and commissional errors were less than 3%. Areas with as little as 1 to 40% spotted knapweed cover were detected with an omissional error of 1% and a commissional error of 6%. Further verification sites were established on August 11, 1998 near Bozeman, MT, using the algorithms developed for Idaho. The omissional error for the Montana sites was 0%, and the commissional error was 10%. The hyperspectral sensor, Probe 1, proved an effective detection tool with the ability to detect spotted knapweed infestations. Nomenclature: Spotted knapweed, Centaurea maculosa Lam. #3 CENMA syn C. stoebe L. and C. biebersteinii DC. Additional index words: Hyperspectral sensor, imaging spectrometer, weed detection, whiskbroom scanner. Abbreviations: Ĉi, commissional error; DGPS, differentially corrected global positioning system; GPS, global positioning system without differential correction; L95, lower bounds expressed as 95% probability interval; Ôi, omissional error; SAM, spectral angle mapper; U95, upper bounds expressed as 95% probability interval.

Tolerance of Several Perennial Grasses to Imazapic1

Although some herbicides are available for control of broadleaf weeds on rangeland, currently no herbicides are registered for selective control of weedy annual grasses in perennial forage grasses. Field experiments were conducted to determine the tolerance of several perennial forage grass species to preemergence (PRE) and postemergence (POST) applications of imazapic, a herbicide that controls certain weedy annual grasses. In PRE studies, perennial forage grasses were seeded 1 d after spraying with several rates of imazapic. The grass species by herbicide rate by location and the grass species by herbicide rate interactions were not significant for plant height and biomass 395 d after treatment (DAT). Expressed as a percentage of the untreated control, imazapic applied at 18 to 140 g/ha reduced height of all grass species 10 to 18%, whereas 280 g/ha of imazapic reduced height 39%. Imazapic applied at 18 to 70 g/ha reduced biomass 12 to 26%. Biomass was reduced 51 and 63% when imazapic was applied at 140 and 280 g/ha, respectively. Thus, rates of imazapic required to control downy brome likely will excessively injure perennial forage grass seeded 1 DAT. In POST studies, imazapic was applied to 1-yr-old stands of perennial forage grass. A dose– response model provided a good fit for grass species biomass and height data. In year 1, biomass and height of orchardgrass, smooth brome, and meadow brome were reduced 14 to 29% more than those of bluebunch, crested, intermediate, and western wheatgrass as imazapic rate increased, which implies that the wheatgrasses were more tolerant to imazapic. However, in year 2, slope of regression lines did not differ among grass species, implying that all forage grass species responded the same to increasing rates of imazapic. Plant height of all grass species decreased 25 to 56% when compared with the untreated control, and biomass decreased 28 to 59% as imazapic rate increased from 18 to 280 g/ha. As discussed previously, rates of spring-applied imazapic required for downy brome control severely injured perennial forage grasses whether applied PRE or POST. The level of tolerance of perennial forage grasses to imazapic depended on herbicide dose and perhaps environmental differences between years. Nomenclature: Imazapic; bluebunch wheatgrass, Agropyron spicatum (Pursh) Scribn. & Smith. #3 AGRSP; crested wheatgrass, Agropyron cristatum (L.) Gaertn. # AGRCR; downy brome, Bromus tectorum L. # BROTE; intermediate wheatgrass, Agropyron intermedium (Host) Beauv. # AGRIN; meadow brome, Bromus erectus Huds. # BROER; orchardgrass, Dactylis glomerata L. # DACGL; smooth brome, Bromus inermis Leyss. # BROIN; western wheatgrass, Pascopyrum smithii Rydb. # PASSM. Additional index words: Biomass, picloram, plant density, tolerance. Abbreviations: DAT, days after treatment; OM, organic matter; POST, postemergence; PP, preplant; PRE, preemergence.

Vegetable crop emergence and weed control following amendment with different Brassicaceae seed meals

Brassicaceae seed meals produced through the oil extraction process release biologically active glucosinolate secondary products and may be useful as a part of biological weed control systems. Before meal can be used most efficiently, recommendations for suitable planting dates that maximize weed control but reduce crop injury must be determined. Our objectives were to determine the impact of 1 and 3% (w/w) meal applications of Brassica napus L. (canola), Brassica juncea L. (oriental mustard) and Sinapis alba L. (yellow mustard) on crop emergence and weed biomass in a growth chamber and field study. Results from the growth chamber experiment indicated that lettuce emergence was reduced by at least 75% when planted into 3% S. alba -amended soil earlier than 5 weeks after meal application. After 5 weeks, emergence was not different among treatments. Crop emergence was not reduced by any meal treatment as compared to the no-meal treatment in year 1 of the field study. In year 2, crop emergence in each 1.2-m row was inhibited by all meal treatments and ranged from 16 plants in the 3% B. juncea treatment to 81 plants in the no-meal treatment. The difference between emergence results in year 1 and year 2 is likely due to differing climatic conditions early in the season prior to irrigation, and the method of irrigation used. Redroot pigweed ( Amaranthus retroflexus L.) biomass was 72–93% lower in 1% B. juncea and 3% treatments relative to the no-meal control in the first weed harvest of year 1. These same treatments had 87–99% less common lambsquarters ( Chenopodium album L.) biomass. By the second weed harvest, redroot pigweed biomass in meal treatments (0.02–1.6 g m −2 ) was not different from that in the no-meal treatment (0.97 g m −2 ). Redroot pigweed biomass in 3% B. juncea plots was reduced by 74% relative to the no-meal treatment in the first harvest of year 2. This treatment also reduced common chickweed [ Stellaria media (L.) Vill.] biomass by 99% relative to the 1% meal treatments. While pigweed biomass was reduced by 3% B. juncea in the early part of the season, by the second harvest this same treatment had the greatest pigweed biomass. Despite significant variability between years, 3% B. juncea did provide early season weed control in both years. Repeated meal applications, however, may be necessary to control late season weeds. Inhibition of crop emergence appears to be highly dependent on the amount and distribution of water and needs to be further studied in field settings.

SULFONYLUREA HERBICIDE RESISTANT WEEDS: DISCOVERY, DISTRIBUTION, BIOLOGY, MECHANISM, AND MANAGEMENT

Sulfonylurea herbicide resistant Lactuca serriola L. (prickly lettuce) plants were discovered near Lewiston, Idaho in April 1987. This was the first confirmed occurrence of herbicide resistance resulting from the use of sulfonylurea. Kochia scoparia (L.) Schrad (kochia) plants from Liberal, Kansas were confirmed as resistant to chlorsulfuron and metsulfuron-methyl in 1988. Since then, sulfonylurea resistant K. scoparia has been identified in eight other States and one Canadian Province. Salsola iberica Sennen & Pau (russian thistle) plants from Kansas, Montana, North Dakota and Washington and Stellaria media (L.) Vill. (common chickweed) plants from Alberta, Canada have also been found to be resistant to sulfonylurea herbicides. Most resistant plants were collected from fields where dryland winter wheat (Triticum aestivum L.) was grown either continuously or in rotation with summer fallow and where chlorsulfuron or chlorsulfuron plus metsulfuron-methyl had been applied at 7 to 14 month intervals for 3 to 5 years. Total sulfonylurea herbicide used ranged from 52 to 200 g a.i.ha-1. Resistant K. scoparia plants have also been collected from noncrop areas where sulfometuron-methyl was applied annually for 3 to 4 years. Total sulfometuron-methyl used ranged from 96 to 425 g ai ha-1. The mechanism of resistance is an altered site of action, acetohydroxyacid synthase enzyme, which is inhibited less in resistant than in susceptible biotypes by sulfonylurea and imidazolinone herbicides. Resistance is not due to differences in herbicide absorption, translocation, or metabolism. Chlorsulfuron-resistant K. scoparia and L. serriola are resistant to several other sulfonylurea and imidazolinone herbicides. However, resistant and susceptible biotypes are usually controlled equally by herbicides with different modes of action. Resistance in L. serriola is controlled by one nuclear gene with incomplete dominance.

PP-604 rate and Avena fatua density effects on seed production and viability in Hordeum vulgare

Abstract High Avena fatua control costs have caused some Hordeum vulgare growers to use reduced rates of herbicides without fully understanding the consequences. Field studies near Moscow and Genesee, ID, were conducted to determine the effect of A. fatua density and PP-604 rate on A. fatua seed production in H. vulgare and on H. vulgare yield. PP-604 treatments were 25, 50, 100, 150, and 200 (minimum labeled rate) g ha−1, and five A. fatua densities ranged from 0 to 386 plants m−2. Visual A. fatua control was greater than 85% with 100 g ha−1 PP-604 at all locations. Data from 1998 were used to construct nonlinear exponential decay and parabolic models to describe the effect of reduced herbicide rates on viable A. fatua seed production and relative H. vulgare grain yield, respectively. At A. fatua densities of 42 to 138 plants m−2, 46 to 71% of the minimum labeled rate of PP-604 reduced seed production 95%. However, an estimated 140 to 235 seeds m−2 were produced at this level of control, which may not ensure a decline in the A. fatua population over the long-term. Hordeum vulgare grain yield was maximum when 70 to 85% of the minimum labeled rate was applied to A. fatua densities of 42 to 138 plants m−2. A higher rate of PP-604 likely will be required to ensure a decline in A. fatua populations over the long-term than needed to obtain maximum H. vulgare grain yield in a single growing season. Nomenclature: PP-604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-2-cyclohexene-1-one; Avena fatua L. AVEFA, wild oat; Hordeum vulgare L. ‘Baronesse’, spring barley.

Allelopathic potential of wild oat (Avena fatua) on spring wheat (Triticum aestivum) growth.

Wild oat plants may produce toxic substances that suppress the growth and development of desirable species, thus accounting for severe yield loss in infested fields. The purpose of this study was to determine the allelopathic potential of wild oat (Avena fatua) on the growth of spring wheat (Triticum aestivum var. Fieldwin) in the absence of plant competition. Wild oat and spring wheat plants were grown separately in 250-ml beakers in a sand medium. Root exudates were extracted from wild oat medium at the 1-, 2-, 3-, and 4-leaf stages of wild oat development and added to beakers containing spring wheat in temporally corresponding stages of development. Spring wheat root and leaf dry weights were measured to determine if one or more allelochemical agents were released from wild oat roots. Spring wheat leaf and root dry weights were significantly reduced by exudates from wild oat plants at the 2- and 4-leaf stages of development, respectively. Allelochemicals were isolated from wild oat root exudates at various stages of plant development. Paper chromatography analysis indicated that at least two unknown compounds were present.Rf values in benzene-acetic acid-water of the two unknown compounds (0.825 and 0.930) were similar to scopoletin (7-hydroxy-6-methoxycoumarin) and vanillic acid (4-hydroxy-3-methoxybenzoic acid), respectively. Additional tests using diazotizedp-nitraniline, ultraviolet absorption spectra, and gas chromatography analysis also indicated that the unknowns were coumarin-related compounds such as scopoletin and vanillic acid.

Biology of common crupina and yellow starthistle, two Mediterranean winter annual invaders in western North America.

Abstract This paper reviews the biology of two closely related Mediterranean annuals, yellow starthistle and common crupina, which have invaded grassland, shrub steppe, and open woodland habitats in western North America. Despite the similarity of their winter annual life cycle, the two species differ significantly in population dynamics. Common crupina has traits that favor persistence rather than rapid population growth: large, heavy achenes with an after-ripening requirement; lower fecundity but higher germination success; and reproduction regulated by vernalization and photoperiod in addition to thermal time. Persistence traits also foster invasion of undisturbed or less degraded steppe habitats. Yellow starthistle has more ruderal traits: small, light, rapidly germinating achenes; higher fecundity, with greater seedling mortality; and reproduction that is less sensitive to photoperiod and vernalization. These characteristics confer a greater adaptability for rapid spread and colonization of disturbance by yellow starthistle than by common crupina. An understanding of the relative differences in biological characters of each species and in their function in invaded environments is relevant to ecological management of these pest species. Nomenclature: Common crupina, Crupina vulgaris Cass., CJNVU; yellow starthistle, Centaurea solstitialis L., CENSO.

Interspecific hybridization : Potential for movement of herbicide resistance from wheat to jointed goatgrass (Aegilops cylindrica)

The transfer of herbicide resistance genes from crops to related species is one of the greatest risks of growing herbicide-resistant crops. The recent introductions of imidazolinone-resistant wheat in the Great Plains and Pacific Northwest regions of the United States and research on transgenic glyphosate-resistant wheat have raised concerns about the transfer of herbicide resistance from wheat to jointed goatgrass via introgressive hybridization. Field experiments were conducted from 2000 to 2003 at three locations in Washington and Idaho to determine the frequency and distance that imidazolinone-resistant wheat can pollinate jointed goatgrass and produce resistant F1 hybrids. Each experiment was designed as a Nelder wheel with 16 equally spaced rays extending away from a central pollen source of ‘Fidel-FS4’ imidazolinone-resistant wheat. Each ray was 46 m long and contained three rows of jointed goatgrass. Spikelets were collected at maturity at 1.8-m intervals along each ray and subjected to an imazamox screening test. The majority of all jointed goatgrass seeds tested were not resistant to imazamox; however, 5 and 15 resistant hybrids were found at the Pullman, WA, and Lewiston, ID, locations, respectively. The resistant plants were identified at a maximum distance of 40.2 m from the pollen source. The overall frequency of imazamox-resistant hybrids was similar to the predicted frequency of naturally occurring acetolactate synthase resistance in weeds; however, traits with a lower frequency of spontaneous mutations may have a relatively greater risk for gene escape via introgressive hybridization. Nomenclature: Imazamox; jointed goatgrass, Aegilops cylindrica Host. #3 AEGCY; wheat, Triticum aestivum L. Additional index words: Herbicide-resistant wheat, hybridization, imidazolinone resistant, interspecific hybrids, introgression, outcrossing, pollen-mediated gene flow. Abbreviations: ALS, acetolactate synthase; BC, backcross generation; DAP, days after planting; PNW, Pacific Northwest.

The Response of Yellow Starthistle (Centaurea solstitialis), Annual Grasses, and Smooth Brome (Bromus inermis) to Imazapic and Picloram1

Competition from annual grasses and yellow starthistle can severely reduce perennial grass forage production and quality in pasture and rangeland. The purpose of this study was to determine yellow starthistle and weedy annual grass control by imazapic applied alone or in combination with picloram, and smooth brome tolerance to these treatments. Sixty days after treatment (DAT) imazapic applied at 70 and 140 g ae/ha reduced annual grass (downy brome, medusahead, and annual bluegrass) plant density and biomass by 66 to 76% compared with the untreated control. Picloram applied at 280 and 420 g ae/ha reduced yellow starthistle plant density and biomass by over 93%. Imazapic applied at 70 and 140 g/ha reduced smooth brome biomass by 79 to 95% at 60 DAT. Picloram did not affect the density or the biomass of annual grasses or smooth brome, whereas imazapic did not markedly affect the density or the biomass of yellow starthistle. Downy brome control increased to a maximum of 97% with increasing imazapic dose (maximum of 280 g/ha) at 30, 60, and 90 DAT. Nomenclature: Ammonium salt of imazapic; potassium salt of picloram; annual bluegrass, Poa annua L. #3 POAAN; downy brome, Bromus tectorum L. # BROTE; medusahead, Taeniatherum caput-medusae (L.) Nevski. # ELYCM; smooth brome, Bromus inermis Leyss. # BROIN; yellow starthistle, Centaurea solstitialis L. # CENSO. Additional index words: Herbicide tolerance. Abbreviations: DAT, days after treatment; OM, organic matter; POST, postemergence.

Effects of Imazethapyr and Pendimethalin on Lentil (Lens culinaris), Pea (Pisum sativum), and a Subsequent Winter Wheat (Triticum aestivum) Crop1

Abstract: Lentil and pea are two important crops grown in rotation with winter wheat in the Palouse region of Idaho and Washington. Imazethapyr plus pendimethalin often is used to control weeds in lentil and pea, but the effects of these herbicides on these crops and the subsequently planted winter wheat crop are not well known. The component and combined effects of several rates of imazethapyr and pendimethalin on growth and yield of lentil and pea and the subsequently planted winter wheat crop were measured in 1997 and 1998 field experiments. No herbicide treatment reduced lentil or pea biomass or seed yield compared with the untreated control. Wheat biomass was reduced 35 to 51%, and grain yield was reduced 11 to 17% in all plots treated with 2,240 g/ha pendimethalin at the lentil hilltop site. Imazethapyr at 106 g/ha plus 1,120 g/ha pendimethalin also reduced wheat biomass 24% at the lentil hilltop site. Wheat was not injured at other sites or by other treatments at the lentil hilltop site. Nomenclature: Imazethapyr; pendimethalin; lentil, Lens culinaris L.; pea, Pisum sativum L.; wheat, Triticum aestivum L. Additional index words: Herbicide persistence, rotational crop safety. Abbreviations: DAP, days after planting; DAT, days after treatment; PPI, preplant incorporated.