Weed Talk

Fleabane- as seen along a roadside near you!

You can read about in a recent edition of the Weekly Times or see it for yourself- it appears to be everywhere! Fleabane is what it is called. There are three main species of fleabane (Conyza spp.) in Australia, namely tall fleabane, flax-leaf fleabane and Canadian fleabane- they are all considered weeds. Fleabanes are an erect annual herb; single stemmed and can reach 2m in height (tall fleabane, flax-leaf reaches 1m when mature). Stems and leaves are covered with fine hairs.  Leaves are grey green and narrow. Flowers are carried in branched heads with each cluster of tiny flowers being enclosed in a series of narrow green bracts.

Seeds are connected to a parachute of fine hairs and seeds only germinate/emerge from (or near) the soil surface. For this reason, the three closely related species are major weeds in minimal tillage cropping systems where the majority of seed remains in the soil surface. Tall fleabane is the more common fleabane in the Gippsland region found along roadsides, horticultural and non cropping areas.

Fleabane Fast Facts;

·         Tall fleabane is edible to native browsers such as wallabies but rarely eaten if other food is available

·         Crimson Rosellas have been reported eating the flowers of tall fleabane along with deer at the beginning of the flowering period

·         Fleabane is rated as having a medium high level impact on high value native vegetation communities in Victoria namely grassy woodlands and volcanic plain grasslands (DPI Weed Risk Assessment 2007). Dense stands of fleabane can smother native grassy vegetation.

·         Each plant can produce up to 110, 000 seeds of which up to 80% can be viable (Widderick and Wu, 2007)

·         Tall fleabane is the main weed of lemon orchards in Portugal (Economou et al, 2002)

·         Seeds don't possess dormancy, in other words they can germinate anytime throughout the year (whenever temperature and moisture requirements are met)

·         The depth of seed burial affects the seed survival of fleabane

o   When sown on the surface, 5% of the seed remains viable after 12 months

o   When buried at 50mm, 10% of the seed remains viable after 12 months

o   When buried at 100mm, 15% of the seed remains viable after 12 months

As seeds only germinate from (or near) the soil surface this is a true survival mechanism

 

Control

Tackling the problem will require a long term approach based on good agronomy and applying integrated weed management principles in order to prevent or retard fleabane resistance to herbicides i.e. use a variety of chemical and non-chemical tactics.

Given that the plant is an annual, producing thousands of seeds, a control program that prevents seed-set is vital. Crop rotations and planting configurations should be managed to maximise competition against fleabane.

Kate Williams 

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