Flaxleaf fleabane (Conyza bonariensis) is the most common of the three fleabane species found in Western Australia. This hard-to-kill weed is rapidly becoming widespread throughout the grain growing regions. Flaxleaf fleabane flourishes in minimum tillage cropping systems, especially in years with good spring rainfall.
Germination usually begins in late August or early September and growth continues after harvest and through summer. Flaxleaf fleabane is a prolific seeder, flowering and setting seed over a long period of time, producing up to 110,000 seeds per plant. These factors, combined with the dispersal of its seed by wind and water over considerable distances, make it a rapidly increasing problem.
In cereal crops, target fleabane seedlings in spring with a late post-emergent application of a suitable broadleaf herbicide.
Fleabane, when mature and under heat or moisture stress, is relatively unresponsive to knock down herbicides, so the best strategy is to control it at the seedling stage during the fallow or in the pasture phase.
When treated young (one month old or less), glyphosate can control susceptible flaxleaf fleabane plants. When mature, however, the weed is very difficult to control with glyphosate, regardless of its resistance status. Treating flaxleaf fleabane after harvest is often ineffective as the plants already have a well developed root system and spray conditions are often far from ideal.
Flaxleaf fleabane can easily establish in and spread from non-cropping areas such as pastures, roadsides and fencelines.
There are no known herbicide-resistant populations of fleabane in WA however there are many documented cases in Australia and overseas of this species being resistant to several herbicide groups.