Lepidoptera : Noctuidae

tomato-fruit-worm_1552965589934

Budworm is Australia’s most destructive and widespread caterpillar pest. It is a pest that has many common names shared between two moth species in the genus Helicoverpa. The common names Corn Earworm, Cotton Bollworm, Tobacco Budworm, and Tomato Grub or Tomato Fruitworm are usually applied to Helicoverpa armigera, and Helicoverpa punctigera is known as Native Budworm. Notably, Corn Earworm (Helicoverpa zea) does not occur in Australia.

The problem is that the caterpillars boring into your tomatoes may be either species, and one or both species is found in all regions of Australia. It takes a trained eye to see the difference between the two, especially at larval (caterpillar) stage. One species, Helicoverpa armigera, is resistant to many of the synthetic insecticides registered against it. However there are some products available that work very well.

Best Treatment for Budworms

To avoid confusion, the best way to treat these two species is to treat them as one and the same. Control of Budworms starts with keeping an eye on your plants, so that you can detect caterpillar damage early. For example you could watch for minor leaf damage in the veggie garden, or Budworm damage to buds and fruit while watering.

For this to work you will need to know what to look for (see Symptoms of Budworm Damage). If you find damage, you should have a closer look to see if you can find the culprits – i.e. caterpillars. To confirm that it is Budworm you will need to know what they 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 Budworms (see How to Prevent Budworms Appearing).

Regular monitoring of your garden will ensure that a major infestation of Budworms doesn’t occur ‘overnight’. This is to be avoided, because Budworm damage can be devastating to plants.

If you want to use a spray, try Yates Nature’s Way Caterpillar Killer - Dipel. The product is based on naturally occurring bacteria (Bacillus thuringiensis), which act as a stomach poison against caterpillars. The product will only affect caterpillars, so your ‘good bugs’ are safe. Follow the label directions and it will work against Budworms in your garden.

What are Budworms &
How to Get Rid of Them

Budworms are the larval stage of 2 moth species – one is native to Australia (Helicoverpa punctigera) and the other is introduced (Helicoverpa armigera).


Description

Adult

Moths of both species have light fawn forewings and light grey hind wings, with a span of about 40 mm. The hind wings have a broad dark band on the outer edge of each wing. This dark band contains the most obvious distinguishing feature between the species - Helicoverpa armigera has a pale patch in the middle of the dark band while Helicoverpa punctigera does not.

Eggs

Dome shaped with a ribbed surface and small (about 1 mm in diameter). The eggs are white in colour when first laid but darken as they develop.

Larvae

Full-size larvae (caterpillars) are about 40 mm in length and have quite a colour range including green, yellow, red, brown to almost black, with a broad yellow stripe down each side of the body and a dark stripe down the centre of the back. The skin has a bumpy appearance and is sparsely covered with long dark hairs.

There are some differences between the two species at the caterpillar stage, but they are not easy to see. Helicoverpa armigera have white hairs around the head, while Helicoverpa punctigera have black hairs around the head. Caterpillars of Helicoverpa armigera also have a dark patch called a “saddle”, just a few segments behind the head.

Pupae

About 20 mm long and orange-brown in colour and usually found in soil.


Life Cycle

Female moths usually lay eggs singly, or in loose groups, on different leaves, flowers or plants. They can lay about 1,000 eggs over their life of a couple of weeks. Eggs can take from about 3 days to 10 days to hatch depending on temperature.

Newly hatched Budworms are very small (1.5 mm) and easily missed on a plant. Caterpillars pass through 6 growth stages (instars) until fully grown (35 - 40 mm long). Mature larvae descend from their host plants and burrow into the soil to pupate. The pupal stage lasts about 2 weeks during warmer months before an adult moth emerges.

In areas that experience cold winters, Budworms usually spend the entire winter underground as pupae.

The life cycle takes one to three months depending on conditions. There are several generations per year with as many as 10 generations in warmer areas of northern Australia.

budworm-ls-elise-dando

(Image courtesy of Elise Dando)

What Plants are Impacted by Budworms

  • Vegetables, including lettuce, tomato and sweet corn.
  • Fruits, including stone fruits and strawberries
  • Ornamental plants, including roses, gardenias, carnations and zinnia.
  • Budworms also feed and breed on many weeds.

Symptoms of Budworm Damage

  • Holes in flower buds and fruit.
  • Leaf damage such as ‘windows’ caused by small larvae feeding on the leaf surface, or holes and tears caused by larger larvae.
  • Damaged silks and cobs of sweet corn, usually with large amounts of caterpillar frass inside the sheath.
budworm-tomato-ls

How to Prevent Budworms Appearing

Monitor

  • Look for buff-coloured moths fluttering around susceptible plants at dusk.
  • Look for buff-coloured moths hiding in foliage during the day. Moths may be flushed out of plants while watering.

Prevent

  • Control weeds. Budworms breed in a number of weeds, especially broadleaf weeds.
  • Cover susceptible plants with fine mesh butterfly netting if you have seen Budworm moths fluttering around.
  • Try to find eggs on leaves and squash them. If the eggs are black, you can safely leave those alone as they have been parasitised by tiny wasps.
  • Pick off minor infestations of caterpillars by hand and squash them. Remove any infested fruits and buds to prevent the pest completing its lifecycle.

Natural enemies

  • Several species of tiny parasitic wasps (see beneficial wasps) attack the eggs of Helicoverpa Eggs which have been successfully parasitised turn black and look very different to eggs which have not been parasitised. If you are unsure, just pick off some leaves with eggs and keep them in a jar for a few days. If tiny wasps emerge, you can safely let them go in the garden. If tiny caterpillars hatch out, there are probably more in your garden also hatching. That is a good time to consider using Yates Nature’s Way Caterpillar Killer - Dipel.
  • Several species of parasitic wasps and parasitic flies lay eggs in or on Budworms and eventually kill them.
  • Many predators attack Budworms. Predatory bugs such as assassin bug, damsel bug and shield bug. Predatory beetles, including carabid beetles and ladybird beetles. Other predators include lacewings and spiders.

Recommended Products to Control Budworms


More articles

Snail & Slug Control in Your Garden

Snails and slugs are unwelcome garden guests that chew holes in leaves of plants and destroy seedlings. Follow our simple methods to avoid major damage.