Time from flowering to seed viability in purple loosestrife (Lythrum salicaria)

L. salicaria is a troublesome invasive species in eastern North America. Co ntrol methods being considered include use of herbicides, phytophagous inse cts and cutting. More effective use of these methods, separately or as an i ntegrated program, requires better knowledge of seed viability for this pla nt which is a prolific seed producer. Infloresences of L. salicaria were collected from an infestation over one g rowing season. Ten inflorescences were collected on each sampling date; fiv e of which were examined while they were fresh and five were allowed to des iccate in a greenhouse under ambiant conditions. Germination tests were per formed on seeds from both fresh and dried inflorescences. From 12 days afte r anthesis (DAA) up to and including 24 DAA, there were no seeds that were germinable on either the fresh or dried inflorescences. At 27 DAA, germinab le seed was first found in the lower 20 nodes of the freshly cut infloresce nces. Above node 20, the inflorescence was in bloom but the seed capsules w ere immature. From 27 DAA on, percent germination from most of the nodes up the stem increased with time. This same pattern was observed in the seeds from the dried inflorescences. Germinable seed was first detected 27 DAA on the dried inflorescences in the lower 10 nodes. As the inflorescences expa nded, the upper nodes matured and germination was not significantly differe nt between the fresh and dried inflorescences. Desiccation of the cut stems of L. salicaria did not affect the germinability of the seeds. There was n o evidence of further maturation and greater seed viability on the dried st ems as compared to the germinability of seeds from freshly cut stems. This indicates that cutting or chemical defoliation of L. salicaria within 3 wee ks of anthesis should destroy the seed crop and prevent additions to the se ed bank. (C)2000 Elsevier Science B.V. All rights reserved.