Sorghum-almum (Sorghum almum Parod. # SORAL) is a weakly perennial, rhizomatous grass that in northern climates reproduces mainly by seeds. Environmental factors influencing seed germination and the longevity of buried seeds were studied in growth chamber and field experiments. Alternating temperatures of 20 C for 16 h and 30 C for 8 h were optimum for germination. Light was not critical to germination. Germination varied only slightly across a pH range from 5.0 to 8.8 but decreased sharply below pH 5. Osmotic potentials greater than −0.9 MPa reduced germination substantially, and no germination occurred at −1.5 MPa. Limited germination occurred at NaCl concentrations of 340 mM, and no germination occurred at 510 mM. Seeds that were either mechanically scarified or afterripened for 6 months had a higher percent germination and germination rate than untreated seeds. Sorghum-almum seedling emergence was 11% from seeding depths of 20 cm, but emergence was 67% or higher from seeding depths of 15 cm or less. In field studies, viability of seeds placed on the soil surface or buried 3 or 8 cm was 2% or less at 12 months and 0% at 18 months after burial. Viability of seeds buried 15 and 23 cm was 0.3 and 26%, respectively, at 24 months after burial. Thus, tillage that buried sorghum-almum seeds 20 cm or more could reduce emergence but would also prolong seed persistence. Shallow tillage should favor depletion of sorghum-almum seed reserves.

Field studies on time of emergence, influence of planting date on growth and reproduction, and winter survival of rhizomes were conducted on sorghum-almum grown in corn and crop-free environments. In 1985, peak emergence of sorghum-almum occurred during early May in crop-free plots and mid-May in corn. In 1986, two peaks of emergence, one in early June and one in late June, were noted in both crop-free and corn plots. Emergence after mid-July was 4% or less of the total emerged in 1985, and no sorghum-almum emerged after mid-July in 1986. In planting date studies, sorghum-almum was seeded alone or in corn at 2-week intervals. Corn competition reduced sorghum-almum shoot, rhizome, and root growth at all planting dates. Maximum sorghum-almum seed production was 43 110 seed/plant when grown without competition but only 1050 seed/plant when grown with corn competition. When grown with corn competition, no seed developed on sorghum-almum seeded 6 or more weeks (mid-June or later) after corn planting. Shoot dry weight of sorghum-almum grown with corn competition was 3 g/plant or less for plants seeded 4 or more weeks (early June or later) after corn planting. Therefore, controlling sorghum-almum in corn through mid-June should prevent seed production and corn yield losses due to sorghum-almum competition. Rhizomes produced by sorghum-almum grown alone or with corn competition did not survive the winter; therefore, in Minnesota, sorghum-almum survival from one growing season to the next depends on seed production.

Uncertainty exists among extension agents and growers in northern Illinois whether a particular sorghum (Sorghum sp.) strain should be identified as johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA] or sorghum-almum (Sorghum almum Parodi. ♯ SORAL). To reduce confusion over its identity, field studies were conducted at Urbana, IL, in 1982 and 1983 to determine if phenotypic differences existed between a johnsongrass strain from Tennessee and the northern Illinois sorghum strain. Three planting dates (May 20, June 3, June 17) were used to determine if time of establishment would affect growth habits and phenotypic expression. Averaged over planting dates, the Illinois sorghum was taller (200 cm vs. 161 cm), produced more seed per panicle (2215 vs. 741), and had a larger shoot to rhizome plus root ratio (2:1 vs. 1:1) and a wider leaf blade (4.6 cm vs. 2.9 cm) than johnsongrass. In contrast, the johnsongrass produced more rhizomes per plant (51 vs. 10) with almost eight times the cumulative rhizome length per plant (778 cm vs. 117 cm). These results were consistent across planting dates. Comparison of chromosome counts from pollen mother cells and root tips showed both johnsongrass and the Illinois sorghum had 2n = 40; thus observed differences between the sorghum strains could not be explained by differences in chromosome number. The northern Illinois sorghum strain more closely resembled sorghum-almum morphologically than the Tennessee johnsongrass.