Galinsoga (Galinsoga parviflora)
Galinsoga is a small, upright annual weed occasionally found in New Zealand lawns, gardens, and nursery beds. It’s less common than weeds like fathen or redroot but can quickly become troublesome in freshly cultivated soil or thin turf.
Also known as Gallant Soldier, galinsoga germinates mainly in spring and early summer, though it can also appear in autumn under mild conditions. It grows fast, flowers early, and drops seed within weeks, allowing several generations to appear in a single growing season. While it rarely dominates lawns, it often pops up in bare spots or areas recovering from renovation or soil disturbance.
Identification
Galinsoga is a small, branching annual that grows 10–40 cm tall. The stems are soft, green, and slightly hairy. Leaves are oval with lightly toothed margins and opposite each other on the stem.
The flowers are the easiest way to identify it. Each tiny bloom has a yellow centre surrounded by five short white petals, resembling miniature daisies. The flowers are about 5 mm wide and often appear in clusters near the top of the plant. Because the white petals are so small, they’re easy to miss unless you look closely.
Two species occur in New Zealand — Galinsoga parviflora and Galinsoga quadriradiata. The latter has slightly hairier stems and leaves with more jagged edges, but both behave the same and are commonly just called “galinsoga.”
Why It’s a Problem in Lawns
Galinsoga grows quickly and thrives wherever the grass is weak or soil is disturbed. In newly seeded or patchy lawns, it can germinate rapidly, flower within weeks, and drop large numbers of seeds before the grass has a chance to recover.
Although shallow-rooted and easy to pull, it can reappear several times through summer if not dealt with early. Its fine seeds spread easily by wind, water, or mower movement, allowing it to pop up repeatedly in garden borders and open lawn patches.
Control in Home Lawns
Because galinsoga is an annual species, control is straightforward if treated early and followed by good lawn care to prevent re-establishment.
Best control methods:
- Physical removal: Hand-pull young plants before flowering. The roots are shallow, and the plant pulls out easily, especially after rain.
- Chemical control: Use selective turf herbicides containing clopyralid (NZLA BWC), bromoxynil, or bentazone for effective control. These actives target seedling-stage weeds before flowering.
- Prevention during renovation: When preparing a new lawn, avoid leaving bare soil exposed for long periods. Keep the area moist and sow grass seed promptly to outcompete weed seedlings.
- Cultural management: Maintain good lawn density with regular fertilising and overseeding to limit open soil where galinsoga can germinate.
Prevention Tips
- Keep lawns thick and well-fed to prevent gaps where weeds can establish.
- Aerate compacted soil annually to promote healthy root growth.
- Mow regularly to remove flower heads before seeds form.
- Avoid spreading contaminated soil or mulch, as galinsoga seeds can travel easily.
- Re-seed bare spots in autumn to establish dense grass before spring germination.