Controlling fleabane in wheat and maize

This winter weed is widespread throughout Southern Africa. It has small seeds and is a shallow germinator.

Due to its invasive nature, tall fleabane can suppress native flora in the open habitats it favours.
Photo: Supplied

Three species of Conyza spp can be a problem in South Africa: Conyza bonariensis (flax-leaf fleabane); C. canadensis (horseweed fleabane); and C. sumatrensis (tall fleabane).

Flax-leaf fleabane can grow up to 1,2m tall and has side branches longer than the main stem. The leaf margins are sharply toothed, and both leaf surfaces are dull green and hairy. The flowers are white and occur in narrow, terminal plumes on the main stem and side branches.

Horseweed fleabane is shorter than the other Conyza species. Like them, it has white flowers, but these are smaller, and the stems branch only at the top of the plant. The leaves are finely toothed, yellowish green and less hairy.

Tall fleabane can grow more than 2m high and its side branches are shorter than the main stem. The flowers are white and the fruits straw-coloured.

All three species are semi-woody with sturdy taproots, and usually occur together.

Control 
Conyza can easily be controlled with shallow cultivation and is therefore not usually a problem in a conventional tillage system. In conservation- or no-till systems, however, it can become a serious threat.

To control the weed, apply either a pre-emergence herbicide before the weed reaches the rosette stage, or a post-emergence broadleaf herbicide. A number of herbicides are registered for the control of Conyza in wheat and maize (see table).

Herbicides registered for the control of fleabane on maize and wheat
Active ingredient Time of application
MAIZE
2,4-D/dicamba Post-emergence of weed and crop, but before the crop
is 30cm tall. Apply when the rosette is smaller than 15cm
in diameter and growing actively.
atrazine/sulcotrione Pre- or post-emergence. When applied post-emergence,
add an adjuvant.
glyphosate Post-emergence, only on glyphosate-tolerant maize.
WHEAT
2,4-d/dicamba Apply between growth stages seven and 13 of the crop.
carfentrazone-ethyl Apply between growth stages seven and 13 of the crop.
dicamba Only for use in tank mixtures with Enhancer (10g to 12g)
and Reaper (10g) and an adjuvant.
metsulfuron-methyl/thifensulfuron-methyl Apply before four- or five-leaf stage of the weed.
glyphosate Pre-emergence.
Pre-emergence.
Note: Some Conyza spp show resistance to glyphosate, and control will therefore vary.

Herbicide effectiveness decreases with an increase in weed size, so try to control the weed before it sheds its seeds. Timing of application is crucial; unfortunately, farmers have often not finished harvesting before it’s the optimal time to spray.

Follow the specific instructions of each product used for spraying the various Conyza spp.

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