To manage or control nonindigenous species (NIS), we need to know where they are located in the landscape. However, many natural areas are large, making it unfeasible to inventory the entire area and necessitating surveys to be performed on smaller areas. Provided appropriate survey methods are used, probability of occurrence predictions and maps can be generated for the species and area of interest. The probability maps can then be used to direct further sampling for new populations or patches and to select populations to monitor for the degree of invasiveness and effect of management. NIS occurrence (presence or absence) data were collected during 2001 to 2003 using transects stratified by proximity to rights-of-way in the northern range of Yellowstone National Park. In this study, we evaluate the use of environmental and remotely sensed (LANDSAT Enhanced Thematic Mapper +) data, separately and combined, for developing probability maps of three target NIS occurrence. Canada thistle, dalmation toadflax, and timothy were chosen for this study because of their different dispersal mechanisms and frequencies, 5, 3, and 23%, respectively, in the surveyed area. Data were analyzed using generalized linear regression with logit link, and the best models were selected using Akaike's Information Criterion. Probability of occurrence maps were generated for each target species, and the accuracies of the predictions were assessed with validation data excluded from the model fitting. Frequencies of occurrence of the validation data were calculated and compared with predicted probabilities. Agreement between the observed and predicted probabilities was reasonably accurate and consistent for timothy and dalmation toadflax but less so for Canada thistle.

Ventenata dubia is an exotic annual grass that has become increasingly invasive in various perennial grass systems throughout the Intermountain Pacific Northwest. Currently, little information is available to landowners about herbicide control options. In our first field study, we evaluated V. dubia control efficacy and perennial grass tolerance of herbicides applied pre-emergence (PRE) at two locations and as an early postemergence (EPOST) application at four different conservation reserve grasslands, with each grassland dominated by different perennial grass species. Treatments included flufenacet plus metribuzin (303 + 76 g ai ha−1 [0.27 + 0.07 lb ai ac−1]), propoxycarbazone-sodium (49 g ai ha−1 [0.04 lb ai ac−1]), rimsulfuron (53 g ai ha−1 [0.05 lb ai ac−1]), sulfosulfuron (53 g ai ha−1 [0.05 lb ai ac−1]), and imazapic (105 g ai ha−1 [0.09 lb ai ac−1]). Rimsulfuron and flufenacet plus metribuzin applied PRE provided > 90% control 10 mo after treatment (MAT). Rimsulfuron and sulfosulfuron applied EPOST provided > 90% control 9 MAT. Herbicide injury to bluebunch and intermediate wheatgrass was negligible across treatments. Imazapic and sulfosulfuron applied EPOST resulted in significant injury to smooth brome and timothy. In our second study, we addressed the following question: Will fall herbicide plus fertilizer treatments improve V. dubia control compared with herbicide treatments alone? We imposed fall herbicide treatments in main plots and fertilizer treatments (fall N, fall P, fall K, fall PK, spring N, NPK) in split plots at three study locations. Herbicide treatments resulted in high levels of V. dubia control. Differences in V. dubia abundance among fertilizer treatments were negligible 9 MAT. Within herbicide control plots, spring N and NPK treatments resulted in significant increases in perennial grass cover and decreases in V. dubia cover (9 MAT). This result indicates that spring N applications timed to the onset of perennial grass growth could be utilized as a component of an integrated management strategy for V. dubia in invaded perennial grass systems.