Published online by Cambridge University Press: 12 June 2017
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 8-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.