Poa annua is an annual grass weed from the large Poa family that tends to act as an annual grass in irrigated situations. This species which is sometimes referred to as “annual winter grass” or “green-keepers curse” is endemic in soils throughout temperate parts of the world. It is a relatively small grass plant which is light green to yellow green in colouration and it seeds prolifically throughout the year. The seeds are white in colour and the leaf blades are soft and often crinkled when young. Poa annua is often confused with poa trivialis which is an annual weed from the same family but is distinguishable by bright green and very shiny leaves. Poa annua seeds prolifically and will seed regardless of cutting height. It is probably the most common grass weed problem for lawns in New Zealand. Typically, it will germinate in the absence of comeptition so is most prevalent on newly established lawns. In the absence of irrigation the plants will die out during the hotter summer months and these plants will not re-emerge. However, in irrigated situations poa annua can behave and persist much in the same manner as a perennial plant. When it behaves in this manner it can be hard to eradicate from temperate grass lawns and several treatments may be required.
- Ryegrass, Tall fescue, N.Z. Browntop: Apply ethofumesate (sold as EXPO 500, Ethosin, Claw, Nortron) at 40mls per 100m2. This will need to be applied twice within 28 days. Repeat application every 3 - 4 months if the infestation is bad. Ryegrass only; Ethofumasate acts as a pre-germination spray and as such can be applied directly over freshly sown ryegrass seed to avoid poa annua germinating. Repeat applications will be required every 3 - 4 months. Fine Fescue lawns: Apply Hasloxyfop-P-Merthyl (sold as Ignite or Gallant) at label rates from September through until April. It is advisable not to use this product in winter as it does have a tendency to discolour the fescue. Couch & Seashore paspalum: Use Kerb at label rates Kikuyu; Use Atrazine at label rates