Broad-leaved Fleabane (Conyza sumatrensis)
Broad-leaved fleabane is a tall, wiry annual weed that’s become more noticeable in New Zealand lawns and garden edges over recent years. It often starts as a small rosette in spring and by late summer can grow over a metre tall if left unchecked. Once it takes off, it quickly dominates thin or neglected areas of lawn, producing thousands of wind-blown seeds that spread easily.
Originally from South America, this weed has adapted well to our conditions, thriving in dry, compacted, or low-fertility soils where grass struggles. Its upright, branching stems are unappealing to grazing animals and just as unwelcome in home lawns, where it creates an untidy, rough appearance.
Identification
Broad-leaved fleabane begins as a flat rosette of green leaves that look similar to narrow-leaved plantain. The difference is in the leaf edges—fleabane leaves have fine, forward-pointing teeth along the margins. As it matures, it sends up tall stems that branch near the top and carry clusters of small, fluffy seed heads. These release huge numbers of light, wind-dispersed seeds, helping it spread quickly around neighbourhoods.
It doesn’t produce yellow flowers like dandelions or other common Asteraceae weeds. Instead, the flower heads are small and pale, turning into soft seed tufts that blow away easily. Once the stems are up, the plant becomes woody and difficult to control.
Why It’s a Problem in Lawns
Fleabane competes with lawn grasses by shading and crowding out weaker areas. It germinates in open soil, especially where lawns are thin, dry, or stressed. Because it produces thousands of airborne seeds, even one neglected plant can lead to new infestations across the property.
In lawns, mowing will usually suppress the tall flowering stems, but unless you deal with the young rosettes, fleabane will return year after year.
Control in Home Lawns
The key to controlling broad-leaved fleabane is timing—treat it while it’s still small and in the rosette stage. Mature plants with woody stems are much harder to kill.
Best control methods:
- Physical removal: Hand-pull or dig out young rosettes before they develop a strong root system. This is easiest after rain when the soil is soft.
- Chemical control: Use a selective broadleaf herbicide containing actives like triclopyr, picloram, or clopyralid for spot-spraying in lawns. Products such as NZLA Gold provide strong control if applied early.
- Non-selective control: For larger infestations or waste areas, glyphosate is effective when the plants are young. However, mature fleabane becomes less responsive, and repeat applications may be needed.
- Prevention: Maintain lawn density through fertilising, overseeding, and consistent watering. Fleabane prefers bare soil, so a thick, healthy lawn will make it much harder for seedlings to establish.
Prevention Tips
- Keep lawns well-fed and regularly mown to stop seed heads from forming.
- Repair bare patches promptly to block seedling germination.
- Avoid letting fleabane go to seed anywhere near your lawn—it spreads fast by wind.
- Consider using a residual herbicide (such as those containing simazine) for hard-to-mow edges or fencelines where fleabane tends to establish.