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The biology of Canadian weeds. 122. Lactuca serriola L

Weaver, S.E., Downs, M.P.
Canadian journal of plant science 2003 v.83 no.3 pp. 619-628
Lactuca sativa, Lactuca serriola, acetolactate synthase, autumn, crops, dormancy, flowering, herbicides, lettuce, overwintering, reduced tillage, seedlings, seeds, spring, summer, weeds, winter, Australia, Canada, Eurasia, Southeastern United States
Lactuca serriola (prickly lettuce, compass plant) is a winter or summer annual, introduced to Canada from Eurasia, and found in all provinces except Newfoundland. It occupies a variety of disturbed sites, and is becoming an increasing problem in crops grown with reduced tillage. Most seedlings emerge in autumn and form overwintering rosettes, with a smaller peak of emergence in spring. Flowering occurs from July through September. Seed production is proportional to stem height, and ranges up to 200 000 seeds per plant. The wind-dispersed seeds have no primary dormancy and form only a short-term seed bank (1 to 3 yr). Many populations in the western United States and southern Australia have developed resistance to Group 2 herbicides, which inhibit the enzyme acetolactate synthase. Prickly lettuce is closely related to, and inter-fertile with, cultivated lettuce, Lactuca sativa L.