Seed capsules of field-grown jimsonweed were harvested 2, 4, 6, and 10 weeks after anthesis. Degree day accumulation from anthesis and weeks after anthesis were equal in predicting the time required for nondormant jimsonweed seed production and seed dry weight. Seed germination increased as capsule age increased from 2 to 6 weeks. No additional increase in germination was observed in seed from capsules collected 10 weeks after anthesis. Maximum seed weight was obtained from capsules 6 and 10 weeks old in 1986 and 1987, respectively. Germination was correlated highly with seed weight.

Weed seeds were germinated in incubators at constant temperatures ranging from 4 to 32 C increments. Percent germination per day was regressed against temperature with the x-intercept representing the low threshold temperature for development. Low threshold temperatures for development (low TTD's) calculated for wild proso millet (Panicum miliaceum L. # PANMI), barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], common lambsquarters (Chenopodium album L. # CHEAL), and redroot pigweed (Amaranthus retroflexus L. # AMARE) were 6.9, 9.7, 6.0, and 10.0 C, respectively.