Maximizing the Efficiency of Invasive Plant Control with a Phenology-Based Timing Approach to Management

Abstract

The control of invasive plants has been the primary concern in ecological and agricultural systems alike for many years, as invasive plants threaten both wildlife habitat and agricultural production. As invasive species continue to move into national parks, wildlife refuges, and ecological preserves, their threat to biodiversity becomes more prominent, thus increasing the need for management and concern of cost. Labor and overall invasive species control has cost the US billions of dollars annually. There is a need for integrated weed management (IWM), which integrates multiple control methods to develop the most efficient management program both economically and ecologically. Plant phenology, the timing of events in the plant life cycle, is an important concept that may help explain the opportunistic and competitive nature of invasive species and provide insight to potential management strategies. Greenhouse and field experiments were conducted on the campus of California State Polytechnic University, Pomona to investigate which stage of growth and development is best to implement a phenology-based mechanical control of Brassica nigra, Bromus diandrus, and Centaurea melitensis. I predicted that applying a cutting treatment at the late stage would have a significant negative effect on the regrowth and seed production of all three species, as plants in later stages of reproduction would be limited in their ability to regrow at the end of the growing season when resource levels are low. I also tested the effectiveness of the mechanical treatment in wet and dry soil conditions and examined seed germination in cut debris material to develop best management practices for phenology-timed control of each species. The field experiment consisted of sixteen plots per plant species randomly assigned one of four mechanical treatments. Treatments included an uncut control and three cutting treatments at three stages of development: early, flowering, and late. One sticky seed trap was placed in each plot to measure seed rain. The greenhouse experiment consisted of thirty-two pots per species with the same mechanical treatments and an additional watering treatment, wet or dry. Soil moisture for the wet treatment was kept at 30% volumetric water content (VWC) and the dry treatment at 15% VWC. I measured maximum height, dry weight, and seed production of regrowth after each treatment during plant senescence. The debris experiment consisted of collecting cut debris for each species at each phenological stage, placing it in a soil flat, watering every two days, and measuring the germination rate. Based on the results of the three experiments the ideal treatment time for B. diandrus was during the flowering or late stage, during the early of flower stage for B. nigra, and during the flower stage for C. melitensis. The time of treatment can change from year to year based on changes in ambient conditions, such as early seasonal precipitation or high temperatures. Debris material should be removed from the field for C. melitensis if possible, but B. nigra material can be left behind when cut at the recommended phenological stage. This research can provide an effective form of phenology based mechanical control for the restoration and agriculture community, providing additional tools in the creation of an IWM program.