Mayweed chamomile is an increasing weed problem in cropping systems of the Pacific Northwest. Modern farming practices that utilize conservation tillage systems and heavy application of nitrogen fertilizers have been associated with increased soil surface water potential and decreased soil pH. Therefore, soil water potential, soil pH, and temperature effects on germination and growth of mayweed chamomile were determined in controlled laboratory tests. Germination of mayweed chamomile in soil was greatest at 30 C and a soil water potential of –25 kPa. Germination and seedling growth were similar in soils with pH 4.7, 5.1, and 6.2. Total plant weight was greatest at 20 C and reduced at 10 and 30 C. Shoot dry weight, as a percent of total dry weight, ranged from a low of 54% at 10 C to 78% at 30 C. A soil moisture potential of –10 000 kPa reduced germination and total plant weight by as much as 95% and 80%, respectively.
