Poa annua

Poa annua is an annual grass weed from the large Poa family that tends to act as an annual grass

Problem Overview

Poa annua is an annual grass weed from the large Poa family that tends to act as a perennial plant 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 coloration and it produces clusters of small white prolifically, throughout the year.

The leaf blades are soft and often crinkled when young. Poa annua is often confused with poa trivialis which is a perennial grass from the same family but is distinguishable by having bright green, 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 competition 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.

Solutions

  • Ryegrass, Tall fescue, N.Z. Browntop: Apply ethofumesate (sold as Ethopro, EXPO 500, Ethosin, Claw, Nawtron) at 40mls per 100m2. Rinse the first treatment off the plants directly after application.  Repeat the application in 14 -21 days. This time allow the product to dry on the plant leaves. Repeat this treatment every 3 - 4 months if the infestation is bad. This will act as a pre-germination treatment to prevent the establishment of additional foreign grasses.
  • Ryegrass only; Ethofumesate acts as a pre-germination spray and as such can be applied directly over freshly sown ryegrass seed to avoid poa annua germinating. Apply a second treatment within 14 - 28 days.  
  • Fine Fescue lawns: Apply Haloxyfop-P-Methyl (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 will have a tendency to discolour the fescue. Do not tank mix this herbicide with any other products. Note that this product is slow activating and several weeks may pass before any effect from this treatment is obvious.
  • Couch: Use the herbicide Kerb at label rates.
  • Kikuyu; Use the herbicide Atrazine at label rates.

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