Timothy S. Prather

A review of remote sensing of invasive weeds and example of the early detection of spotted knapweed (Centaurea maculosa) and babysbreath (Gypsophila paniculata) with a hyperspectral sensor

Abstract Remote sensing technology is a tool for detecting invasive species affecting forest, rangeland, and pasture environments. This article provides a review of the technology, and algorithms used to process remotely sensed data when detecting weeds and a working example of the detection of spotted knapweed and babysbreath with a hyperspectral sensor. Spotted knapweed and babysbreath frequently invade semiarid rangeland and irrigated pastures of the western United States. Ground surveys to identify the extent of invasive species infestations should be more efficient with the use of classified images from remotely sensed data because dispersal of an invasive plant may have occurred before the discovery or treatment of an infestation. Remote sensing data were classified to determine if infestations of spotted knapweed and babysbreath were detectable in Swan Valley near Idaho Falls, ID. Hyperspectral images at 2-m spatial resolution and 400- to 953-nm spectral resolution with 12-nm increments were used to identify locations of spotted knapweed and babysbreath. Images were classified using the spectral angle mapper (SAM) algorithm at 1, 2, 3, 4, 5, and 10° angles. Ground validation of the classified images established that 57% of known spotted knapweed infestations and 97% of known babysbreath infestations were identified through the use of hyperspectral imagery and the SAM algorithm. Nomenclature: Babysbreath, Gypsophila paniculata L. GYPPA; spotted knapweed, Centaurea maculosa Lam. CENMA.

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.

Time and Temperature Requirements for Weed Seed Thermal Death

Abstract Mortality of weed seeds at temperatures of 39, 42, 46, 50, 60, and 70 C was recorded through time under controlled laboratory conditions similar to those of soil solarization for six weed species: annual sowthistle, barnyardgrass, black nightshade, common purslane, London rocket, and tumble pigweed. Time and temperature requirements for thermal death varied considerably among the species studied. Barnyardgrass, London rocket, and annual sowthistle were more susceptible to heat treatment than black nightshade, common purslane, and tumble pigweed. Temperatures of 50 C and above were lethal for seeds of all species. Common purslane seeds were unaffected at 46 C and below, tumble pigweed and barnyardgrass seeds were unaffected at 42 C and below, and black nightshade seeds were unaffected at 39 C. Nonlinear models for mortality as a function of duration of heat treatment were developed for each species at each temperature at which mortality occurred. These models provide an empirical relationship for the construction of field-applicable decision models that could predict the accumulation of time and temperature combinations for effective solarization of weed seeds. Nomenclature: Annual sowthistle, Sonchus oleraceus L. SONOL; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; black nightshade, Solanum nigrum L. SOLNI; common purslane, Portulaca oleracea L. POROL; London rocket, Sisymbrium irio L. SSYIR; tumble pigweed, Amaranthus albus L. AMAAL

Detecting the Locations of Brazilian Pepper Trees in the Everglades with a Hyperspectral Sensor1

Brazilian pepper is a small evergreen tree that forms dense colonies. It was introduced for horticultural use in the United States in the early 1800s and was widely distributed in Florida in the late 1920s. Previous remote-sensing projects to detect Brazilian pepper achieved moderate success and warranted additional research using a hyperspectral sensor. Detection with remote sensing is desirable because complete access to ground survey crews is not practical. The western half of the Everglades National Park was imaged at a 5-m spatial resolution with a hyperspectral sensor by Earth Search Sciences Inc. of Kalispell, MT, on December 12, 2000, and January 10, 2001. The sensor has 128 channels and spectral resolution between 450 and 2,500 nm. The purpose of this research was to develop spectral reflectance curves for Brazilian pepper and establish the accuracy of classified images. Classified images showed that a hyperspectral sensor could detect a “pure” Brazilian pepper pixel representing the center of an infestation but not “mixed” Brazilian pepper pixels at the sparsely populated edges. To define the sparse populations, images were classified using a spatial buffer (15- to 100-m radius) based on a low–omissional error image. A 25-m buffer reduced the amount of commissional error for Brazilian pepper in mangrove-dominated forest to 8.2% and buttonwood-dominated forest to 0%. Wider buffers did not significantly improve image accuracy when compared with the 25-m buffer distance. Results indicate that removal crews using hyperspectral images will be able to reliably find the colonies of Brazilian pepper but will not be able to use the images to find isolated scattered trees. Nomenclature: Brazilian pepper (Schinus terebinthifolius Raddi) #3 SCITE. Additional index words: Hyperspectral sensor, imaging spectrometer, invasive plant detection, whiskbroom scanner. Abbreviations: GPS, global positioning system without differential correction; PLOS, posteriori least-squares orthogonal subspace projection; SAM, spectral angle mapper; USGS-BRD/SERP, United States Geological Survey—Biological Resource Division/Southeast Environmental Research Program.

Predicting the likelihood of yellow starthistle (Centaurea solstitialis) occurrence using landscape characteristics

Abstract Yellow starthistle is an invasive plant species common in the semiarid climate of central Idaho and other western states. Early detection of yellow starthistle and estimation of its infestation potential in semiarid grasslands have important scientific and managerial implications. Weed detection and delineation of infestations are often carried out by using ground survey techniques. However, such methods can be inefficient and expensive in detecting sparse infestations. The distribution of yellow starthistle over a large region may be affected by various landscape variables such as elevation, slope, and aspect. These exogenous variables may be used to develop prediction models to estimate the potential for yellow starthistle invasion into new areas. A nonlinear prediction model has been developed using a polar coordinate transformation of landscape characteristics to predict the likelihood of yellow starthistle occurrence in north-central Idaho. The study region included the lower Snake River and parts of the Salmon and Clearwater basins encompassing various land-use (range, pasture, and forest) categories. The model provided accurate estimates of yellow starthistle incidence within each specified land-use category and performed well in subsequent statistical validations. This prediction model can assist land managers in focusing their efforts by identifying specific areas for survey. Nomenclature: Yellow starthistle, Centaurea solstitialis L. CENSO.

Evaluating Restoration Methods across a Range of Plant Communities Dominated by Invasive Annual Grasses to Native Perennial Grasses

Abstract Prairies are imperiled habitats, with remnants being generally small and often existing in isolation. Invasive plants have the potential to invade not just the edge of small remnants but also the interior because smaller remnants experience greater edge effects than do large, contiguous prairies. Additionally, invasive plants limit recruitment of native plants, which can arrest secondary succession. We proposed to assess techniques for restoration that included removing annual grasses and supplementing native species recruitment with seeding of native grass and forb species. We also assessed the effect of specific factors affecting recruitment: soil moisture and seed predation. Treatments included broadcast, spot, or no application of the herbicides imazapic and glyphosate and with or without seeding plus mulch. With treatments nested within each of three plant communities, ranging from annual- to perennial-dominated communities, in four blocks per community, plant characteristics (percentage of cover and plant density), soil moisture availability, and seed-predation losses were measured along a plant community gradient within one season at two locations. A combination of broadcast herbicide application and seeding with mulching was found to be more effective in reducing annual grasses and enhancing the establishment of native grass species in predominately annual and mixed communities (annuals and perennials). Spot herbicide application was effective in predominately perennial communities, whereas only seeding native species did not improve recruitment. Although seed predation reduced seedling recruitment, mulch provided seed protection and enhanced soil moisture retention. Plant community response to imposed treatments differed among communities, suggesting that a decision support tool would facilitate management decisions tailored for each plant community. The decision tool would be useful to ensure that appropriate treatments are applied and that specific factors affecting recruitment, such as seed predation and soil moisture, are addressed. Nomenclature: Glyphosate; imazapic. Interpretive Summary: Restoration of grasslands in the Pacific Northwest from annual, nonindigenous plant–dominated communities to native, perennial plant–dominated communities is impeded by loss of viable native perennial seed reserves and by competition from the nonindigenous annuals. Addressing those challenges within the framework of a decision mechanism that considers initial plant community composition would allow restoration strategies tailored to emphasize techniques appropriate to the challenges faced. Our study assessed techniques for restoration within Palouse Prairie that included removing annual grasses by broadcast and spot-herbicide applications and supplementing native species recruitment with seeding of native grass and forb species across a plant community gradient. We also assessed seed predation and soil moisture as specific factors affecting plant recruitment. The results showed that response to treatment differed for annual and perennial grasses and forbs among the plant communities. High seed predation, ranging from 40 and 85% was observed. Although seed predation was associated with the observed low recruitment of native perennial grasses, mulch seemed to provide seed protection and enhanced soil moisture retention. The results enabled us to develop a decision mechanism that suggests (1) predominately perennial plant communities do not benefit from added seed, but spot herbicide treatment can reduce annual grass cover; (2) broadcast herbicide applications are required in mixed plant communities, even when foliar cover of perennial grasses approaches 20%; and (3) predominately annual plant communities should be seeded along with the use of a broadcast herbicide application. Decision mechanisms focused on foliar cover and density of dominant plant species can inform restoration efforts within the Palouse Prairie and are likely useful within other Pacific Northwest grasslands as well.

Uptake, translocation and metabolism of aminocyclopyrachlor in prickly lettuce, rush skeletonweed and yellow starthistle.

BACKGROUND Aminocyclopyrachlor is a new herbicide proposed to control broadleaf weeds and shrubs in non-crop and rangeland systems. To gain a better understanding of observed field efficacy, the uptake and translocation of foliar-applied aminocyclopyrachlor (DPX-MAT28) and aminocyclopyrachlor methyl ester (DPX-KJM44) were evaluated in two annuals, prickly lettuce (Lactuca serriola L.) and yellow starthistle (Centaurea solstitialis L.), and one perennial, rush skeletonweed (Chondrilla juncea L.). RESULTS Absorption and translocation varied between species. While absorption of DPX-KJM44 was greater than absorption of DPX-MAT28, rush skeletonweed absorbed the most, followed by yellow starthistle and prickly lettuce. Overall, the total translocation of either herbicide was highest in yellow starthistle, followed by rush skeletonweed and prickly lettuce. Proportional herbicide movement between species was similar, with the majority translocating to developing shoots. However, in rush skeletonweed, early translocation was directed to root tissue. In rush skeletonweed, no DPX-MAT28 metabolism occurred, while DPX-KJM44 was rapidly de-esterified and translocated as DPX-MAT28. CONCLUSION Aminocyclopyrachlor absorption and translocation are dependent on active ingredient structure and species sensitivity. Highly sensitive species such as prickly lettuce absorb and translocate less material than relatively less sensitive species such as rush skeletonweed. De-esterification of DPX-KJM44 appears to delay translocation of the resulting acid in yellow starthistle and rush skeletonweed.

Sudex cover crops can kill and stunt subsequent tomato, lettuce and broccoli transplants through allelopathy

Grass cover crops can be harvested for biomass or used as a surface mulch to reduce erosion, improve soil structure, suppress weeds and conserve moisture. There is concern, however, that such plantings may affect subsequent crops. We studied the effects of sudex, a sorghum hybrid used as a cover crop, on subsequent crops of tomato, broccoli and lettuce started from transplants. Within 3 to 5 days of being transplanted into recently killed sudex, all three crops showed symptoms of phytotoxicity including leaf necrosis, stunting and color changes. There was 50% to 75% transplant mortality in all three species. Plant growth and development, as determined by biomass measurements, were also significantly affected. Yields of mature green tomato fruit and marketable broccoli and lettuce heads were reduced significantly. Tomato, broccoli and lettuce should not be transplanted into sudex residue for at least 6 to 8 weeks, or until the residue has been thoroughly leached.

Winter mortality of Aceria chondrillae, a biological control agent released to control rush skeletonweed (Chondrilla juncea) in the western United States

Abstract:  Classical biological control of weeds is based on the assumptions that: (1) plant species are in part invasive in their introduced range because of the absence of coevolved specialist herbivore arthropods and plant pathogens; and (2) that these specialist herbivores can regulate host‐plant populations. Although the need for quantitative post‐release monitoring studies testing these assumptions has been acknowledged repeatedly, the number of assessments is still remarkably small and usually restricted to systems with notable impact of an agent species. However, studying systems where biological control agents cause no observable target weed reductions may be important to identifying factors that limit the population size or impact of biological control agents. Three biological agents were released for the control of the herbaceous perennial rush skeletonweed, Chondrilla juncea in North America between 1975 and 1977. Although all three species are widely established, weed densities are increasing and there is little quantitative information on factors limiting biological control efficacy. We examined the winter biology and survivorship of the rush skeletonweed gall mite Aceria chondrillae at two rush skeletonweed field sites in south‐western Idaho over 2 years. Gall mite winter mortality was high (>90%) in both years and for both sites. Gall mites were more abundant on plants that produced rosettes in fall and rush skeletonweed plants growing on southern aspect were 3.4 times more likely to produce rosettes than those growing on northern aspects. Our data suggest that A. chondrillae population densities are limited by its high winter mortality. The gall mites may require fall rosettes to successfully survive the winter, which are commonly absent on north‐facing aspects, impairing the efficacy of A. chondrillae to control rush skeletonweed in the intermountain western United States.

Ecological Characteristics of Ventenata dubia in the Intermountain Pacific Northwest

Abstract Ventenata dubia is an exotic winter annual grass that has invaded Conservation Reserve Program (CRP) lands, improved pastures, intensively managed hay fields, and rangelands within the Intermountain Pacific Northwest (PNW). Currently, producers are attempting to develop V. dubia management strategies with little knowledge of its life history traits. We conducted several studies to characterize V. dubia life history patterns. Preliminary germination trials were completed to describe primary and secondary dormancy characteristics. Field studies were conducted to evaluate (1) seed bank persistence patterns, (2) seedling emergence patterns under V. dubia litter, and (3) seedling emergence and phenological development patterns within timothy hay, CRP, and rangeland habitats. Preliminary germination trials suggest that the after-ripening period required for loss of dormancy does not exceed 30 d and that dormancy breakdown peaks at approximately 90 d, after which germination occurs over a wide range of temperatures (9 to 29 C). A small fraction (< 1%) of the seed bank remained germinable up to 3 yr after burial at 2 cm depth in a grassland habitat. Seedling emergence and survival was significantly greater under high V. dubia litter layers (100% cover) compared with bare surface during the drier study year because of higher soil moisture levels maintained under litter. Across habitat types, mean seedling emergence (50% of total) occurred between 33 and 94 growing degree days (GDD) after soil moisture rose above the permanent wilting point in the fall. Seedling emergence periodicity varied among habitat types in relation to spring seedling emergence, ranging from 0 to 13% of total emergence per year. Phenological development differed across sites and years by up to several hundred GDDs but was closely aligned to Julian days. This collection of studies improves our understanding of V. dubia life history traits and will aid integrated weed management strategies in the Intermountain PNW. Nomenclature: North Africa grass; Ventenata dubia (Leers) Coss.; timothy; Phleum pratense L. Management Implications: Ventenata dubia is an exotic annual grass that has invaded established CRP lands, improved pastures, intensively managed hay fields, and rangelands within the Intermountain PNW. Significant economic and ecological impacts have resulted from V. dubia invasions across perennial grass habitats in recent years, underscoring the need for development of integrated control strategies. Control of V. dubia using selective herbicides within perennial grass stands, as well as cultural control strategies, will benefit from greater understanding of V. dubia life history patterns. Within the Intermountain PNW, V. dubia seedling emergence occurs after fall rains have increased soil moisture above the PWP in timothy hay, CRP, and rangeland habitats. The greatest proportion of fall seedling emergence occurs within 6 wk of initial emergence. Spring seedling emergence is more likely in timothy hay and rangeland habitats where fall environmental conditions are less conducive for seedling emergence and survival in the Intermountain PNW. At a local scale, seedling emergence and survival is likely mediated by the amount of residue at the soil surface. Higher V. dubia litter levels will increase seedling emergence and survival compared with bare surface during drier or colder fall growing seasons. A small fraction of V. dubia seed banks (< 1%) may remain persistent, or germinable, for up to 3 yr at shallow soil depths (2 cm). These life history traits should inform V. dubia management strategies in the Intermountain PNW. Ventenata dubia may be controlled with early postemergence herbicide applications in late fall. However, this application timing is often a narrow window for growers because of unpredictable weather conditions. Predictive models of seedling emergence patterns can be used to time pre-emergent or early postemergent applications to temperature and soil moisture conditions. Additional research is needed to identify herbicide control options for fall applications that could potentially provide soil residual control of spring-emerged seedlings. Predictive models of phenological development may also be used to time cultural control strategies that aim to reduce or prevent V. dubia seed production, such as targeted mowing in CRP or altering hay harvest schedules. Cultural control strategies that target the seedling phase of V. dubias life cycle should focus on litter management techniques, such as prescribed burning, to eliminate the benefits of litter on seedling recruitment. Because of low levels of seed bank persistence, integrative control strategies should be planned for several years (> 3 yr) to reduce the negative effects of V. dubia on managed perennial grass systems across the Intermountain PNW.