Sod webworm is small caterpillar of the Crambus moth species, of which there are hundreds of known varieties, they can cause massive amounts of damage when they form in large numbers and each female can lay up to 200 eggs. Sod webworms are usually uncommon in Australia due to the fact that most of the grasses we grow for home lawns are Warm Season Grasses, and these caterpillars overwhelmingly prefer Cool Season Grasses.
Despite this, sod webworms can and do invade Australian lawns, and their damage can be most noticeable in healthy green lawns when small brown or straw coloured patches begin appearing which are between 1 - 15 centimetres in diameter. Damage from infestation can be more difficult to see when the lawn is subject to drought, as the damage is often the same colour as dying lawn, or grass which is becoming brown due to lack of water.
If an infestation of sod webworm is suspected, the first step to proper diagnosis would be to check the lawn in the mornings, looking for signs of silken webs over the lawn while there is still dew present. If further investigation is required, the lawn must be checked at night time, first look around for small moths which may be flying around. The next thing to do will be to take a torch and get down on hands and knees, and open up the thatch layer of the affected areas. If sob webworm is present, this is when they are to be found, usually munching away inside the lower thatch layer of the turf. Sod webworm can be many different colours, but usually have a different coloured head to that of it's body, they are usually between 15-25 mm in length when they are most active and discovered.
Controlling or killing sod webworm is a relatively straight forward process of applying a chemical pesticide to the lawn just before sunset. The chemical is then watered lightly into the lawn so it reaches as deep as the thatch layer. When the sod webworm begins feeding it was also ingest the pesticide.
For severe infestations, control is absolutely vital, otherwise the infestation will grow at a phenomenal rate. And while the damage caused never affects the crowns of the lawn which would result in the lawn dying, the damage can still be so severe that a lawn looks completely devastated as a result.