The Coefficient of Germination Velocity (CGV) is a measure of the number of seeds germinating in a period of time. Generally, the CGV increases as more seeds germinate that have shorter germination times. The results show that cheatgrass germination velocity is decreased by 5 µM and 10 µM ABA (Table 2; Figure 2). Percent germination was calculated as the number of seeds germinating divided by the total number of seeds in a treatment. The only effect on percent germination was 10 µM ABA decreased germination of yellow starthistle when compared to the control (Table 3; Figure 3). with 5.0 ml of distilled water or a test solution. The dishes were placed in a growth chamber at 20 0 C with a photoperiod of 12 hours. Three replicates of 20 (CG and SL) or 10 (YST) seeds were tested for each treatment in a randomized complete block design. Distilled water was added to the germination paper when required to keep the paper moist (1 ml approximately once each week). Germinated seeds were counted and removed each day for 28 days. Percent germination, Coefficient of Germination Velocity (CGV) and Mean Germination Time (MGT) were calculated for each treatment and control by species using the methods of Scott, et al The statistical significance of these values was determined by One Way Repeated Measures Analysis of Variance and pairwise multiple comparisons were determined by the Student- Newman Keuls means separation test. Statistical analyses were carried out using SigmaStat (v. 3.10, Systat Software, Inc., 2004). The level of significance for all statistical tests was set a priori at α ≤0.05. Introduction The Department of Army manages approximately 14 million acres of land for military use. The presence of invasive plant species can impair military operations by limiting training activities due to a loss of realistic training conditions; by causing habitat destruction and biodiversity loss; and, by creating security and safety risks. In short, the presence of invasive species affects sustainable, mission-oriented land management activities on Army lands. While commercially available growth regulators are commonly used to suppress seed germination and reduce vegetative growth in turfgrass, very little research has been done looking at the use of growth regulators for the control and management of invasive weeds. In order to improve sustainable vegetation management on Army training lands, two plant growth regulators, abscisic acid (ABA) and gibberellic acid (GA) were evaluated for their effects on the germination of cheatgrass (Bromus tectorum), yellow starthistle (Centaurea solstitialis) and Sericea Lespedeza (Lespedeza cuneata) seeds. The Effects Of Plant Growth Regulators On Invasive Species Michael L. Denight 1, Dick L. Gebhart 1, Ryan R. Busby 1, Aaron G. Hager 2, and Steven J. Taylor 3 1 U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory, 2902 Newmark Drive, Champaign, IL ; 2 Department of Crop Sciences, University of Illinois, Urbana, IL 61801; 3 Division of Biodiversity and Ecological Entomology, Illinois Natural History Survey, Champaign, IL For further information For more information about this project, please contact Michael Denight, ERDC-CERL TreatmentMeanStd DevSEM Control a µM ABA a µM ABA b µM ABA 8.32 c Table 2. One Way Repeated Measures Analysis of Variance results for CGV of cheatgrass. Mean values with different letters are significantly different at the 0.05 level. Materials and Methods A series of growth chamber experiments were conducted to determine the effects of phytohormones on seed germination of cheatgrass (CG), yellow starthistle (YST), and Sericea Lespedeza (SL). Gibberellic acid and abscisic acid were dissolved in 2 ml ethanol, then brought to volume with distilled water to make a 100 µM stock solution. The stock solutions were then diluted to 1, 5, and 10 µM GA or ABA. An ethanol control (0 µM GA or ABA) had the same ethanol concentration as the other solutions. Seeds of each of the three species were placed in 100 mm sterile polystyrene Petri dishes (100 x 15 mm) containing 2 layers of germination paper moistened Results The ethanol blank did not differ from the control for any treatment, so the control was used for comparison. The GA treatments did not differ from the control at the various concentrations for any of the invasive species. The MGT of cheatgrass was greater than the control at the 5 µM and 10 µM ABA concentrations (Table 1; Figure 1). MGT is the average amount of time (in days) it takes for seeds to germinate. TreatmentMeanStd DevSEM Control 2.02 a µM ABA 2.05 a µM ABA 6.40 b µM ABA c Between Treatments F=49.92 (P < 0.001) Table 1. One Way Repeated Measures Analysis of Variance results for MGT of cheatgrass. Mean values with different letters are significantly different at the 0.05 level. Figure 1. Mean Germination Time of cheatgrass seeds treated with different concentrations of ABA. Figure 2. Coefficient of Germination Velocity of cheatgrass seeds treated with different concentrations of ABA. Between Treatments F=93.79 (P < 0.001) TreatmentMeanStd DevSEM Control a µM ABA a µM ABA a µM ABA b Between Treatments F=5.583 (P = 0.036) Table 3. One Way Repeated Measures Analysis of Variance results for percent germination of yellow star thistle. Mean values with different letters are significantly different at the 0.05 level. Figure 3. Percent germination of yellow starthistle seeds treated with different concentrations of ABA. Conclusions The results of this study show that ABA inhibits seed germination in cheatgrass and yellow starthistle, while GA had no effects on any invasive species at low concentrations. The reduction in cheatgrass germination due to ABA application may reduce the competitive advantage of this invasive species on disturbed lands. A reduction in both MGT and CGV at concentrations of 5 µM and 10 µM ABA indicates that treating cheatgrass infested areas may give native plants time to become established before cheatgrass germinates. Future research will investigate the ability of ABA to reduce germination of cheatgrass under field conditions. Both field studies and greenhouse studies are being designed to determine if ABA reduces germination in cheatgrass under field conditions in competition with native plant species.