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 onionw eed 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 fr om 18/11 to 30/23 C day/night. The greatest biomass was produced at da y temperatures of 18 or 24 C and night temperatures of 11 or 17 C. Lea f production and reproductive development were greatest at 18/11 C. Pl ants 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 photoperio ds. Climatic analyses revealed no U.S. analogs of the principal Austra lian onionweed sites. Based on its environmental responses and its pat tern of distribution as a weed in Australia, onionweed will likely rem ain confined to the southwestern U.S.