PhD Defense Seminar: Vera Vuković

“Integrative Approaches to Managing Smooth Crabgrass (Digitaria ischaemum): Germination Dynamics, Population Responses, and Control Options in Turfgrass”

Abstract: Smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] is one of the most troublesome annual grass weeds in cool-season turfgrass systems. This research aimed to improve understanding of smooth crabgrass seed dormancy, population differences, herbicide sensitivity, and cultural management to support integrated weed management (IWM) strategies. Studies on seed dormancy demonstrated that primary dormancy is regulated by both physical and physiological mechanisms. Light quality and chemical scarification had minimal effects on germination, whereas mechanical removal of seed covering structures increased germination to as much as 97%, indicating that these structures impose major constraints on germination. Hormone profiling revealed differences between dormant and nondormant seeds, particularly within covering structures, where dormant seeds contained higher concentrations of compounds associated with dormancy maintenance. Further, stratification and seed burial studies were conducted to evaluate the effect of temperature and moisture on dormancy release. Cold, moist stratification rapidly alleviated dormancy, whereas dry storage at 4°C maintained dormancy. After-ripening at 23°C also reduced dormancy but at a slower rate. Dormancy release patterns also differed among populations, as hydrothermal time modeling revealed that the Arkansas population exhibited greater dormancy persistence and reached HTT₅₀ at approximately two months later than populations from Iowa and Indiana. These population-specific differences prompted investigation of U.S. population by seed dormancy. A common garden study of twelve populations originating from diverse U.S. climates revealed significant variation in vegetative growth, flowering phenology, reproductive output, and seed morphology. Hierarchical clustering separated populations into two primary clusters, largely corresponding to latitude of origin. Flowering phenology and seasonal vigor contributed most to clustering patterns. Four herbicide resistant populations were included in the common garden experiment; however, no measurable fitness penalty was detected among these populations. Further evaluations showed that populations resistant to herbicide quinclorac remained susceptible to herbicides with different modes of action including fenoxaprop-ethyl and mesotrione, suggesting lack of multiple resistance. Finally, cultural management studies demonstrated that higher mowing heights and appropriate nitrogen fertilization enhance turfgrass competitiveness and diminish smooth crabgrass establishment. More data will be presented.