Yellow bristle grass
WHAT YOU SEE IN SUMMER:
kids on holidays, the beach, ice cream, barbecues.
WHAT I SEE IN SUMMER:
yellow bristle grass.
Yellow bristle grass ( Setaria pumila or YBG) comes from a family of annual grasses, which includes foxtails and millets. It’s originally from Asia and has spread through Europe, North America and Australasia.
Over the last few years, possibly driven by the ‘pugging’ or compaction of wet soil in winter, YBG has spread through Taranaki, Waikato, Auckland, and the Bay of Plenty, moving from roadsides into pasture.
YBG is a C4 photosynthetic plant. This means it grows more vigorously at higher temperatures than nutritious pasture plants like ryegrass and clover. It spreads during summer dry periods, then dies out in winter, leaving bare patches of soil. These tend to grow weeds, and become reinfested with YBG in spring.
YBG seeds germinate from midOctober (when soils are about 16°C), peaking by mid-november (when soil temperature is over 20°C). This is similar to other C4 weeds such as summer grass, crowsfoot grass and smooth witchgrass. However, YBG is far more invasive and competitive due to its size and seed numbers per plant.
Seed heads appear from late December through to February. Once they do, it’s too late to spray as their hard coating protects them. They disperse in water, hay, on animals, and in contaminated crops like maize. They lay dormant for about three months before they can germinate. However, germination is driven by soil temperature, so you won’t see the worst of an infestation until the following spring.
The seeds can last in the soil for up to 10 years, but are generally only viable for a few years.