The signs
On the Central Coast this is a January to March problem, sometimes running into April in a warm year.
- The lawn thins out or looks scalped without having been mowed short.
- Brown patches that spread noticeably from one day to the next.
- Leaf blades chewed ragged along the edges, or eaten down to the stem.
- Birds working the lawn hard — magpies and ibis will find grubs before you do.
- Bright green grub droppings sitting in the thatch at the base of the grass.
The overnight test
Wet a hessian sack, an old towel or a piece of carpet and lay it flat on an affected part of the lawn in the evening. Lift it early the next morning.
Army worms shelter in the thatch during the day and feed at night, and the damp cover brings them up to the surface. If they are there, you will see them straight away. This test costs nothing and removes all the guesswork.
Treating them
- Use a product registered for lawn grubs and army worm, and follow the label rates exactly. Over-applying does not work faster and does damage the lawn.
- Apply late in the afternoon or early evening. That is when the grubs come up to feed, so that is when the treatment reaches them.
- Water it in as the label directs. Most granular products need it to move down into the thatch where the grubs are.
- Treat the whole lawn, not just the brown bit. Army worm moves as a front, so the grass ahead of the damage already has them in it.
- Check again in a week. A second application is sometimes needed for a heavy infestation.
Getting the lawn back
Grubs eat leaf, not roots. As long as the crown and runners survived, a warm-season lawn will come back on its own with water and a light feed once it is growing again. Give it a few weeks of warm weather before you write any patch off.
If a patch stays completely bare after a month of good growing conditions, the roots have gone and it needs re-turfing.
Catching it early
The advantage of a regular mowing round through summer is simply that someone is standing on your lawn every fortnight. Army worm damage caught in the first few days is a treatment. Caught a fortnight later it can be half a lawn.