Watch out, Army worms about! What to look for and what to do next..

I dont recall ever having seen Army worm on the south coast before and had learnt about it primarily through the numerous complaints from Sydney residents on the NSW Lawn fanatics page made each year when their lawns were unexpectedly destroyed. But this year, Army worm has been well and truly on the march down the coast and has hit us here in the Eurobodalla.

Have a look at the damage done below in just 16 days when army worm was left unchecked in this lawn in Lilli Pilli!

Almost unrecognizable. The only green left is from weeds that have taken advantage and are no longer being smothered by the turf!

So, what is an Army worm and what does it do? Simply put, its a type of caterpillar. But its a caterpillar that lives in the lawn and feeds on the leaf blade of your lawn instead of plants in your garden.
Unfortunately though, with no leaf, the lawn dies.

So, how do you spot Army worm and what do you do when you think you have it? Army worm is most often identified in the lawn once it has made a considerable impact on a patch of lawn. This can be as simple as an area that appears to be ''recently mowed’ however upon closer inspection the leaves are chewed and not cut. This can also be an obvious sign for the home occupier if they havnt mowed a random patch of their lawn recently.

The area affected is often ‘squishy’ to walk on. The caterpillar lives within the soil and in significant numbers it loosens the soil substantially making it quite soft to walk on.

When you walk the lawn, you might see a number of small light grey butterflies taking off and / or landing within the lawn. This is unfortunately a sign you have army worm and are likely to have a whole lot more.

The army worm moth will lay its eggs (numbering between 100 to 200) in a small brown stack appearing to be covered in hair. Often this nest is made within dense bush however it can often be on hard surfaces like walls, fences and the eaves of a house. These often appear like hairy mud splats but are a solid indicator of army worm infestation.

Finally, if you or a neighbour has had an infestation for a while, you might see a number of red wasps flying about the lawn. These are a parasitic wasp that lay their eggs in the caterpillar and are on your side in controlling an infestation however usually by the time they’re around your lawn is probably already a mess. Have a look below at the images of signs of lawn damage.

Heres a patch of lawn clearly caterpillar affected. The lawn has died back and the lengths of the leaf blades in the centre area are considerably shorter than those around it.

Here you can clearly see the blades of grass have been chewed, similar to a leaf thats had bites taken out of it!

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Here you can the soil is clearly quite loose. To touch, it has been disturbed almost as if its been cultivated by a tiller but instead its just housed a number of caterpillars actively moving about underneath.

Not an award winning photo but this is one of the ‘hairy mud splats’ on a colourbond fence.

This little nest contains 100 to 200 little caterpillars. On the fence were hundreds of these egg sacks.

A simple way to check and confirm if you are indeed suffering from army worm, beside visual inspection of the lawn, is to conduct a ‘soapy water test’. This test is simply flooding an affected area with water that contains a small amount of dish soap. You can even do this test without the soap and just flood the area with water however the addition of soap significantly improves the results. What you will very quickly see is the insects living in the lawn coming to the surface for air. These insects often include worms, crickets and spiders as well as Army worm if it is present.

A simple bucket containing about 20 litres of water and a small amount of dish soap.

And here they are. Moments after dumping the bucket of soap on the lawn, these two juvenile army worm popped their heads up. I tested multiple sites and at each site plenty of caterpillars popped up to get some air.

Below I have a short video of walking a lawn and spotting the small grey butterflies fluttering about. This video is the same lawn I did the soapy water test on and observed the above photographed grubs. The second half of the video is simply showing that flooding a lawn can also provide results albeit a little slower.

Finally, what can you do to stop it? Thankfully, thats easy. Numerous products exist that are both preventative and post infection solutions.
Acelypryn is a product readily available as both a liquid and granular to treat both and prevent infestations of harmful lawn pests including Army worm. Acelypryn can provide protection for up to 6 months. The active in Acelypryn is a Chlorantraniliprole.
Bifenthrin is a chemical used to immediately kill active lawn grubs and other lawn pests. Bifenthrin provides no residual protection so ongoing observation of the lawn should be conducted to make sure no grubs return.

Unfortunately, Acelypryn is reasonably expensive so its not something everyone rushes out to purchase each season.

Bifenthrin comparatively is quite cheap so atleast treating an active grub infestation is achievable without breaking the bank.
Something to consider though is that Bifenthrin will kill almost all living insects (regardless of whether or not they’re beneficial) so a lot of caution should be utilised in its application. Bees in particular should be avoided and spraying around flowers should be avoided. When I treat lawn grubs, I aim to spray towards the evening when most of the days beneficial insects are less active.

Below is an example of a hose on solution of bifenthrin by Richgro. You’ll notice the image on the bottle is an adult army worm to really help with the identification of the pest.

Not a product I am affiliated with, just a simple off the shelf solution as an example. It is also available a sa granular that you let rest and then hose in 24 hours later.