Temperature and photoperiod effects on onionweed (Asphodelus fistulosus) and its potential range in the United States

Environmental factors that affect the growth and development of onionweed were evaluated in order to predict its potential range and impact in the U.S. In controlled-environment experiments, onionweed achieved 60 to 100% of its maximum vegetative growth at temperatures ranging from 18/11 to 30/23 C day/night. The greatest biomass was produced at day temperatures of 18 or 24 C and night temperatures of 11 or 17 C. Leaf production and reproductive development were greatest at 18/11 C. Plants eventually flowered also at 18/17, 24/17, and 24/11 C but not in any regime with a 30 C-day or a 23 C-night. Flowering occurred earlier in 16-h photoperiods than in 16-h photoperiods than in g-h photoperiods. Climatic analyses revealed no U.S. analogs of the principal Australian onionweed sites. Based on its environmental responses and its pattern of distribution as a weed in Australia, onionweed will likely remain confined to the southwestern U.S.