Lepidoptera : Noctuidae
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.
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.
Budworms are the larval stage of 2 moth species – one is native to Australia (Helicoverpa punctigera) and the other is introduced (Helicoverpa armigera).
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.
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.
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.
About 20 mm long and orange-brown in colour and usually found in soil.
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.
(Image courtesy of Elise Dando)