The most common grub which damages lawn in this region is the lawn army worm. It will become rampant from now until the weather cools down. Army worms attack the soft new growth of fresh roots causing sick patches of lawn that get bigger day by day.
Lawn army worm looks more like a caterpillar than a worm. It is khaki coloured and can grow to approx. 2.5cm.
If you are unsure whether you have lawn army worms, you can identify them by flooding a small area of lawn. They will come to the surface. Or, put a wet bag down in the evening and the lawn army worm will be sheltering under it when you turn it over in the morning.
Lawn army worms are like flies – you are not going to get rid of them you just learn to live with them. If you get rid of them they will quickly reinfest your lawn from another property down the road. They are always there.
The best prevention is to keep your grass growing consistently without any major flushes of growth. Flushes of growth mean soft new root growth which the lawn army worms love. To do this use slow release fertiliser or organic fertiliser which is naturally slow release. Have a regular fertiliser programme you stick to. Fertilise in February/March, June, and October/November. Do not fertiliser in December/January as this is usually when we get the natural flush of growth associated with rains.
If lawn grubs are already invading your lawn and the tell-tale signs of sick lawn are appearing, then you will probably have to resort to chemicals to control them.
Apply product (available in granules, hose on or concentrate) in the evening when the lawn army worm comes into the lawn growing media to feed. They bury deep in the soil during the heat of the day and the chemicals cannot penetrate deep enough to affect them and have dissipated by the time the lawn army worm comes to the surface in the evening. At least two treatments are required as the first attack has eaten the roots and the recovery growth of new roots is like sugar to ants.
All lawns newly planted in the summer season should be closely observed and treated as necessary. Once established, certain species of grass handle lawn army worms better than others. Buffalo grass with its consistent growth pattern and coarse root growth and Tropika seem to handle a huge lawn army worm population without showing any detrimental effect. Zoysias with high silica content also handle grubs reasonably well. Hybrid couch (Winter Green, Legend etc) with high requirement of fertiliser seem to be the worst and require constant treatment.
But remember, the best prevention is to keep your grass growing consistently.