Noctuidae

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Cutworms are the larvae of moths from the genus Agrotis. There are about 9 species in the genus found in Australia and 3 of those are pests. They are the:

  • Common Cutworm (Agrotis infusa) – the ‘Bogong Moth’
  • Pink Cutworm aka Brown Cutworm (Agrotis munda)
  • Black Cutworm aka Greasy Cutworm (Agrotis ipsilon)

Common Cutworm is found in the southern half of Australia, including Tasmania. A significant number of the adults (‘Bogong Moths’) in south-eastern Australia migrate to mountainous country to shelter over summer. Pink Cutworm and Black Cutworm are found throughout Australia. Black Cutworm is thought to be resident in warmer sub-tropical and tropical parts of Australia, and migrate into southern regions during the warmer months there.

The adult moths of Cutworms are completely harmless and feed on nectar from flowers. Cutworm larvae do all the damage. Larvae feed on a wide range of plants including lawn grasses, vegetables and ornamentals (especially at seedling stage), and broadleaf weeds.

Best Treatment for Cutworms

The secret to pest control is to keep an eye on your plants, including your lawn, so that you can detect pest incursions early. For example you could watch for disappearing seedlings in the veggie garden, and keep an eye out (see Monitor) for Black Cutworm damage when mowing your lawn. For this to work you will need to know what to look for (see Symptoms of Cutworm Damage). If you find damage you should have a closer look to see if you can find some insects. If you find insects you will need to know what Cutworms look like (see Description).

Prevention is always better than cure, and you are more likely to be able to achieve that if you are out and about in your garden regularly. There are several things that you can do to prevent serious damage from Cutworms (see How to Prevent Cutworms Appearing).

Regular monitoring of your lawn and garden will ensure that a major infestation of Cutworms doesn’t occur ‘overnight’. All treatments are way more effective if you can catch an infestation in its early stages.

Try Yates Grub Kill and Protect for the control of Black Cutworm larvae in lawns. The product also controls other lawn caterpillar pests including Lawn Armyworm and Sod Webworm; and lawn beetle pests including Curl Grub, African Black Beetle larvae, Argentinian Scarab larvae, Argentine Stem Weevil larvae, and Billbug larvae.

 

What are Cutworms & How to Get Rid of Them

Cutworms are the larvae (caterpillars) of moths. They are called ‘cutworms’ because of their habit of lopping seedlings off at ground level and then feeding on the fallen foliage.

Description:

Adults:

Common Cutworm (Agrotis infusa) adult moths – ‘Bogong Moths’ - are dark brown in colour, and they fold their wings along their body when at rest. They have a wingspan of about 40 to 50 mm. There is a distinctive dark arrow shaped marking overlaid by 2 lighter spots on each forewing. Hindwings are pale with darker edging.

Pink Cutworm (Agrotis munda) adult moths are grey brown in colour and they fold their wings along their body when at rest. They have a wingspan of about 40 mm. Their wings have a grey brown pattern overall. There is a dark arrow shaped marking overlaid by 2 lighter spots on each forewing, along with a black wedge shaped marking nearer the body. This black wedge shape differentiates the Pink Cutworm moth from the other two moths described here. Hindwings are pale with darker edging.

Black Cutworm (Agrotis ipsilon) adult moths are brown to black in colour, and they fold their wings along their body when at rest. They have a wingspan of about 40 to 50 mm. The outer one-third of each forewing is a light brown colour, while the inner two-thirds of each forewing is dark brown to black. There is a distinctive dark arrow shaped marking overlaid by 2 dark ringed spots on each forewing. Hindwings are pale with darker edging.

Eggs are similar for all species: white to yellow, ribbed, and roughly spherical about 0.5 mm in diameter.

Larvae when they first hatch are about 1 to 2 mm long but grow to about 40 mm long. The colour of mature larvae varies from dark grey to greenish-brown to black, without obvious hairs, and a somewhat ‘greasy’ appearance. Pink Cutworms often have a reddish tinge. Common Cutworms and Black Cutworms are similar in appearance and difficult to tell apart.

Pupae are similar for all species: spindle-shaped, about 20 mm long and dark brown.

Life Cycle:

Adults moths are active at night and may be drawn to outside lights. Eggs may be laid singly on grass blades (particularly Black Cutworms), or in clusters of about 30 eggs on the leaves of garden plants, or in damp plant debris on the ground, or in cracks in the ground. Female moths are capable of laying over 1,000 eggs over their life span of a few weeks.

Larvae go through 5 moults before reaching their maximum size 2 - 3 weeks later. Larvae hide in tunnels in the soil, or under clods, during the day and crawl out to feed at night. Mature larvae chop off seedlings at ground level and haul the fallen foliage down into their tunnels to feed on it during the day. Larvae pupate in the soil and emerge as a new generation of moths a couple of weeks later.

The entire life cycle can be completed in about 6 weeks during warm weather. There may be as many as 4 overlapping generations per year depending on the climate. Cutworms overwinter as pupae.

What Plants are Impacted by Cutworms

Cutworms are pests of:

  • seedlings, especially vegetables.
  • lawn grasses (especially by Black Cutworms).
  • established vegetables with a dense growing habit such as celery and broccoli.

Cutworms have also been recorded feeding on weeds such as dock, dandelion and thornapple.

Symptoms of Cutworm Damage

  • The more mature (i.e., bigger) the larvae are the more damage they do.
  • Black Cutworms in lawns – look for brown spots about 50 mm wide with a tunnel entrance hole in the middle. This is caused by the larva chewing off all the green blades of grass and taking them down the tunnel.
  • Seedlings chopped off in the veggie garden or flower beds.
  • Furrows and gouges in the stems of vegetables such as celery and broccoli. Sometimes caterpillar frass (droppings) is also present.

How to Prevent Cutworms Appearing

Monitor

  • Look for Cutworms crawling around in the veggie patch at night.
  • Black Cutworms – go out at night with a torch to look for larvae coming out of holes in the lawn.
  • Black Cutworms – examine any brown patches which form in lawns.
  • Identify moths drawn to outside lights at night.

Prevent

  • Cut off some plastic drink bottles to place over seedlings as protective collars against Cutworm attack.
  • Control weeds to prevent Cutworms breeding in them.
  • A well cared-for lawn is more able to resist Black Cutworm attack and recover from it than an unhealthy lawn. Always water and fertilize appropriately for the type of lawn you have.

Natural enemies

  • Several parasitic wasps are known to target Cutworms eggs and larvae. These wasps need a feed of nectar before laying eggs. You can encourage them by having nectar bearing flowers in the garden for them to feed on.
  • Predatory damsel bugs, shield bugs, carabid beetles, ladybirds and lacewing larvae feed on Cutworm eggs and larvae.

Recommended products to control Cutworms


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