Abstract
(1) Erigeron canadensis is one of several annual colonizing species in the eastern U.S.A. that typically germinate under a crop canopy during summer and autumn, overwinter as vegetative rosettes, then 'bolt' and flower the following summer. (2) Populations of E. canadensis were monitored over a 2-year period for seed input and germination, seedling survival, and flower and seed production. (3) Seedlings in two field populations in Illinois growing at low densities suffered only 1 Y mortality prior to the first frost in November. However, the populations suffered severe mortality in winter (16-86%4), due to frost heaving. (4) Winter survival correlated closely with rosette size, and ranged from O% for small rosettes up to 1OO survival of rosettes in large diameter-classes (>5 cm). (5) At maturity, 80%. of the E. canadensis individuals exhibited symptoms of aster yellows, a mycoplasma disease transmitted by the aster leaf hopper (Macrosteles fascifrons). As a result, seed production was reduced by 53%.
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