Common groundsel adapts readily to new environments and selection pressures and has been variably described as both a winter and summer annual. We characterized germination response to temperature in seeds from populations occurring at six sites along a 700-km north–south transect (Kentucky to Michigan). Seeds were collected in 2000 and 2002 from randomly selected plants (350 to 400), at each sampling site. Two germination patterns were observed: (1) seeds from the southern locations averaged 80 to 90% germination across the range of 5 to 25 C; and (2) seeds from northern locations had reduced germination when incubation temperatures were close to 5 or 25 C. When seed from all locations were grown in a common environment (14/10-h thermoperiod of 22/18 C), their progeny had a germination response that was similar across the temperature gradient, regardless of original location, suggesting germination of the parent seed was due to maternal environmental effects. In a subsequent experiment, common groundsel was grown in growth chambers with warm long days (22/15 C and 16 h of light), warm short days (8 h of light), cold long days (15/8 C and 16 h of light), and cold short days. Eighty percent of seeds from the warm environments germinated across the range from 5 to 25 C indicating that these maternal conditions had produced nondormant seeds. In contrast, 20% or fewer of the seeds from plants in the cold chambers germinated regardless of temperature, suggesting that dormancy had been induced by the cool maternal environment. Results also indicated that signaling of maternal environment varied with inflorescence development stages, meaning the earlier the inflorescences are exposed to cold conditions, the lower the percent germination in F1 seeds. Preventing seed maturation on common groundsel growing under cool conditions may reduce the formation of a persistent seed bank.

Common groundsel is an alien annual weed that has become increasingly troublesome in many crops in Ohio. Understanding the periodicity of seedling emergence and longevity of seeds buried in the soil may help growers devise more efficient strategies to control common groundsel. Studies were conducted to determine the dormancy status of common groundsel seeds over 24 mo, and to describe the effect of tillage and fertilizer on the pattern of seedling emergence and the rate of depletion of seeds from the soil seed bank. Common groundsel seeds were collected (June 2000 and 2002) from sites along a 700-km transect from Kentucky to Michigan (39°1′ and 43°36′N, respectively). Seeds were cleaned and placed in nylon mesh bags for burial in a common garden. Every month for the following 24 mo, replicate bags from each location were exhumed. Germination was tested under alternating temperatures of 20 and 10 C, for 14 and 10 h day/night, respectively. Germination response at each sampling date was similar regardless of seed source, but differed for the 2000 to 2002 and 2002 to 2004 experiments. Laboratory germination of seeds buried was initially high (98%) and declined rapidly to about 20% by midwinter. Germination increased to about 60% during the second summer, followed by a slow decline to 40% during winter and another rapid decline before the third summer. The rapid declines in germination were preceded by low soil temperatures (<5 C) and the germination peaks corresponded with periods of high soil temperatures (∼ 20 C). Results suggested that common groundsel follows a cycle of dormancy and nondormancy corresponding to decreases and increases, respectively, in soil temperature. During 2 yr of deep burial in undisturbed soil, 94% of the seeds germinated or died, suggesting that common groundsel seeds may not persist more than a few months in regularly disturbed soils.

Control of the annual weed, common groundsel, may be troublesome because of insufficient control by herbicides. Biological control based on stimulating epidemics of the rust fungus Puccinia lagenophorae on common groundsel populations may be an alternative to herbicides if the rust fungus can be integrated with the general use of herbicides against other weeds. Formulations of monolinuron, metoxuron, and pendimethalin were selected for the study. The integration of the rust fungus with each of the three herbicides was evaluated. A three-step procedure was followed to evaluate the integration of the rust fungus and these formulated herbicides. The effect of the selected herbicides on common groundsel was tested in the first step. Only formulated monolinuron completely controlled common groundsel under controlled conditions, indicating that biological control is not required in situations where monolinuron is employed for weed control. The effect of metoxuron and pendimethalin on the rust fungus was tested under controlled conditions in the second step. Formulated metoxuron was not compatible with the rust fungus, indicating that biological control cannot be employed in situations where metoxuron is applied. The effect of pendimethalin on P. lagenophorae epidemics was evaluated using an epidemiological model in the third step. Formulated pendimethalin had no detectable effects on P. lagenophorae epidemics. We concluded that use of P. lagenophorae epidemics for common groundsel control is complementary to application of formulated pendimethalin against other weeds.