Weed life history: identifying vulnerabilities - Ecological Management of Agricultural Weeds - page 73

Figure 2.6 Distribution ofestimated seed production by 231 individuals of
Amaranthus retroflexus in no-till sweet corn plots.(C.L.Mohler & M.B.Callaway,
unpublished data; see Mohler & Callaway,1995.)
growing with minimal competition, though some produce 10000 to 25000
seeds per plant (Stevens, 1932; Salisbury, 1942), and a few like Salsola iberica
and Echinocloa crus-galli may produce over 100000 seeds per plant (Young,
1986; Norris,1992).Afew annuals (e.g., Veronica hederifolia) produce fewer than
100 seeds per individual (Salisbury, 1942; Boutin & Harper, 1991). Stationary
perennial weeds show a similar range in seed production to annuals (Stevens,
1932; Salisbury, 1942), except that monocarpic perennials (biennials) tend to
produce more seeds (Stevens, 1932), probably because the observed reproduc-
tive output is based on resources captured over more than one season of
growth.Comparable data for wandering perennials are lacking,but given that
they allot resources to vegetative spread,their seed production probably tends
to be less on a per ramet basis. Some wandering perennials (e.g., biotypes of
Cynodon dactylon ) produce no viable seeds at all (Horowitz, 1972; Kigel &
Koller, 1985).
Although most weed species potentially produce very many seeds per
plant, the actual productivity in a crop is usually much less. C. L. Mohler & M.
B. Callaway (unpublished data) found that Amaranthus retroflexus produced up
to 253000 seeds per plant, but that individuals emerging in unplanted plots
in July as effects of an atrazine application dissipated averaged only 770 seeds