Lawn Armyworm Marches on Queensland: What Haven’t Gardeners Learned?

Armyworm, Spodoptera
Armyworms are on the march in suburbia, devouring lawns in their path. ABC Sunshine Coast, by Annie Gaffney and Kylie Bartholomew, 28.2.20.

“Ripe weather conditions in south-east Queensland are being blamed for an “explosion” of armyworms chomping through lawns within days”, reports ABC News.

My Brisbane lawn has armyworm most years, yet it remains green and thriving. What is it about my lawn that makes it so verdant and so different from the others?

“John McDonald, biosecurity manager at Greenlife Industry Australia — the national peak body for the nursery industry…said while the grass was not dead and would grow back, it could be distressing for residents. “We are seeing pockets of armyworms exploding in recent weeks and those populations … people have not witnessed that before.”

Mr McDonald said he even had them at his Brisbane home for the first time in 20 years. “In recent weeks we’ve had hundreds end up in our pool, so we’ve never seen that before. It was somewhat of a surprise to see such large numbers and find them moving out of the neighbour’s yard into ours.”

Nambour resident Katelyn Efremoff had a similar experience when she noticed her neighbour’s lawn turn brown days before the worms munched through hers”.

Armyworms are on the march in suburbia, devouring lawns in their path’,  ABC Sunshine Coast, by Annie Gaffney and Kylie Bartholomew, ABC News.

How can gardeners respond?

Once the armyworm have matured, they pupate in the soil and emerge as moths. If the weather remains warm humid and damp, they lay more eggs in turf. In a warm climate, there may be time for a second generation to repeat their life cycle before laying overwintering eggs which wait for next season to hatch.

Directors Lawn
The Director’s lawn, Sydney Botanic Gardens: Professional shame hits hardest when it’s the new bosses’ lawn that looks like it has been sprayed with herbicide.

When I managed Sydney Botanic Gardens lawn armyworm demolished the Director’s lawn during my first autumn. The lawn he and his guests looked out across turned brown. The risk of attack is highest during periods of warm weather following heavy rain when grass growth surges. And the professional shame hits hardest when it’s the new bosses’ lawn that looks like it has been thoroughly sprayed with herbicide.

At that point I had only worked at the gardens for a few months, so we applied the standard quick fix. The all important cultural controls would have to wait.

We sprayed the lawn with Bt (Bacillus thuringensis), an organic-approved biological control that’s widely sold. That stopped the armyworm marching off to feast on an adjacent lawn.

People do crazy things to control lawn armyworm: dousing the lawn in soap flakes or persistent poisons isn’t kind to soil life, especially worms, a critical part of sustainable turfculture and horticulture. These responses make matters worse.

After applying Bt, we cored the lawn to help aerate the soil. We applied granular poultry manure at the recommended rate and thoroughly watered it in. In other people’s gardens, especially public ones, I use granular poultry manure because it loses its odour faster than the pelletised form. We roped off the turf from foot traffic to protect new growth. Within three weeks it was recovering: pleasantly covered with green growth.

Any home gardener can replicate this. If you don’t use a mechanical corer, use a fork to aerate the topsoil.

Cultural controls

The all important cultural controls are adjusting the soil pH to be a slightly acidic pH6.5, to aerate the turf twice yearly, to feed the turf with poultry manure once in spring, summer and autumn, and to cut the lawn as high as your mower permits. The resultant healthy, vigorous turf rhizomes are fully charged with energy to bounce back after having been ‘grazed’ by armyworm. Just as Mr McDonald said to ABC News, only I have given you key information to better manage turf before an attack in a way that significantly reduces the recovery period.

And you now know how to halt armyworm before it moves next door. You know how to be a good organic neighbour.

How can a lawn have armyworm and yet remain healthy, green and growing?

It took seven years of consistent sustainable garden management for my garden to establish a stable garden ecology. That stable ecology effectively manages most pest outbreaks, including lawn armyworm.

This stable ecology includes pests, predators of pests, and parasites of both pests and predators. There’s a reason why 80% of all caterpillars that are ever born in Australia never make it to adulthood – a biodiverse garden ecology includes Tachinid flies. Thanks to expert entomologists at Museums Victoria, I have identified five species of Tachinid in my garden. All are happy to have armyworm on the menu.

Australian Leafroller Tachinid, Trigonospila brevifacies
Australian Leaf-roller Tachinid is so effective at caterpillar control it has been exported to New Zealand.

The Australian leaf-roller Tachinid, Trigonospila brevifacies, is Species 477 in my biodiversity inventory. This is such an economically valuable parasitoid of a number of late stage moth and butterfly larvae that it was deliberately introduced into New Zealand as a biocontrol of several pests, including the apple moth (Epiphyas postvittana) and potato tuber moth (Phthorimaea operculella).

I have three species of Rutilia fly. These big, sometimes brightly coloured flies occur in small numbers but their larvae control not only armyworm and other pest caterpillars, they control lawn beetle larvae. There are six introduced species of beetles whose grubs feed on roots and rhizomes of grasses and vegetables. Damage by these pests also occurs in warm weather after heavy rain. The harm they do may be misdiagnosed as armyworm damage. Rutilia flies are incredibly handy allies to conserve. They help put food on the table AND keep that lawn healthy and green.

The bird-dropping spider, Celaenia excavata (syn. C. kinbergii), Species 452, specialises in hunting armyworm moth. Adults escape predation by mimicking bird droppings. Females are nocturnal hunters, using a single thread to hang down from a branch overhanging a lawn. They release a pheromone which mimics the sex scent released by the female armyworm moth. When a male moth approaches, the spider is ready with a fatal embrace. This handy to have spider occurs along Australia’s eastern and southern coasts.

Gardening Australia filmed this spider in my garden after another wave of lawn armyworm was munching its way through the suburbs of Brisbane in 2015.

Images with notes and information links of most of the 530-odd species of animal which visit or live at my subtropical garden are held on my Public Facebook Page in the album ‘Curious Garden Creatures‘.

There is more than one species of lawn armyworm and not all feed at night. Sometimes on a cloudy day you can see blades of grass quiver before they fall and get eaten. That’s the kind of attack my lawn sustains from these pests – they thin my lawn but they don’t devastate it. Thanks to my sustainable gardening practices and the myriad of beneficial allies that protect my garden from the disaster illustrated by ABC News.

Last year, I held a sustainable turfculture workshop at the Trevallen Lifestyle Centre and I’ve given talks on this topic at the Queensland Garden Expo. If you’re interested in learning how to grow a healthy, vigorous, sustainable lawn which remains mostly green during drought like mine and is capable of resisting lawn armyworm, I recommend viewing the stories I have recorded with Gardening Australia:

* ‘Love your lawn’, Series 26 Episode 20;
* ‘Reinvigorate your lawn’, Series 19, Episode 36;
* ‘Little lawnmowers’, Series 29 Episode 11;
* ‘Winter lawn care’, Series 16 Episode 19;

I’ll let ABC Sunshine Coast into the secrets of success. Seems they need to watch Gardening Australia.

Bellis subtropical summer
Lawn armyworm can be managed sustainably – if you know how.

Happy autumn!

Jerry Coleby-Williams
Director, Seed Savers’ Network Inc.
Patron, National Toxics Networks Inc.
Patron, Householder’s Options for Protecting the Environment (HOPE) Inc.
1st March 2020

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