Germination and emergence characteristics of prickly lettuce (Lactuca serriola L.)

Prickly lettuce (Lactuca serriola L.) has become an increasing problem in cereals and lucerne pastures in southern New South Wales, Australia. A better understanding of the biology is needed for improved control. Laboratory and field experiments were conducted to determine dormancy status among L. serriola populations, to evaluate environmental factors affecting seed germination and to determine field emergence patterns. Among 76 L. serriola seed samples collected between 2015 and 2018, more than 59% of the samples had little or no innate dormancy, with germination greater than 80%. However, a further tetrazolium test showed that 42 samples collected in the summer season of 2015-16 differed in their dormancy status, with high levels of initial dormancy up to 75.6% in some populations. Lactuca serriola germinated from 10 C to more than 35 C, with the optimum temperatures being 15-25 C. Light stimulated the germination of L. serriola, while the germination was completely suppressed at 80-110 mM of NaCl. Lactuca serriola germinated well under a range of acidic and alkaline conditions. L. serriola predominately emerged (40-52%) from the soil surface, however, limited emergence also occurred from beyond 5-cm burial depth (up to 1.5%). Emergence in a standing crop was 10 times less than that in a bare soil. L. serriola populations from high and low rainfall zones had similar seasonal emergence patterns in the field, with 69% emergence in late autumn and early winter, 22-26.8% in late winter, 1.4-2.4% in spring in the first year after sowing, little or limited emergence in the second and third year. These results suggest that L. serriola can colonise wide geographical areas. Controlling the autumn and winter cohorts is important to stop seed set. If the seed set is completely prevented, L. serriola can be managed over a minimum of two years due to the relatively short-lived seed life.