Corn earworm
Helicoverpa armigera
The larvae of corn earworm (CE), also known as cotton bollworm or tomato grub, is a major pest of cotton and can also be problematic in pulses and canola. They can cause significant damage to all stages of plant growth but are most damaging in late spring and summer. CE are widespread across Australia, however are more common in northern and coastal regions of eastern Australia. CE have developed high levels of resistance to insecticides, therefore an integrated approach to management is essential.
Description
Adult moths are light-brown to red, with several dark markings and have a wing span of 30 - 45 mm. Hind wings are pale with a dark band along the edge and a characteristic small pale spot. Females can lay up to 1000 eggs, usually in the top third of the plant, in growing points. Larvae at maturity reach 40 mm, ranging in colour from brown, green and orange, with bumpy skin. White hairs surround the head and black hairs are visible along the body. Up to 4 - 5 generations can occur in a season. Larvae activity is temperature dependent, being more active in warm conditions, and when temperatures fall below 12 °C feeding ceases and pupae enter a diapause. CE are occasionally carnivorous and may eat each other. They appear very similar to native budworm and lesser budworm; a microscope is needed to distinguish between the two.
The most severe seedling damage occurs when the terminal bud is attacked. In older plants CE are most damaging when feeding on fruiting parts and seeds, which causes holes in seed pods or heads. In cotton, damage is common to squares, flowers and bolls. Significant yield losses result from feeding on seeds/grains, which reduces seed weight and grain quality.
Control
Several natural enemies against CE exist including; shield bugs, damsel bugs, assassin bugs, native earwigs, tachinid flies, orange caterpillar parasite, two-toned caterpillar parasite, parasitoid wasps, lacewings and spiders. Some naturally occurring fungal diseases can also play a role in controlling CE. Where possible, minimise the use of broad-spectrum insecticides to conserve predator populations.
Cultivation at the end of the season, also known as ‘pupae busting’, disrupts the pupal stage, which can be helpful in managing CE populations. If small-medium sized larvae are present, canola can be windrowed and pulses desiccated to accelerate crop drying, which may reduce damage to seeds. Several genetically modified (GM) crop varieties produce a natural toxin targeting larvae and in these crops, CE are generally not observed to be an issue.
CE has developed resistance to several insecticides, therefore proper identification is vital when considering chemical control options. Attract and kill formulations target the moth stage and can be useful in reducing CE populations. Biopesticides have shown to be effective in crops with a narrow flowering window, such as sorghum. In cotton, growers should follow the resistance management programs available. A timely application of insecticide should be made when larvae are smaller (7 mm) and good coverage is essential for control.
Decis Options® is registered for the control of corn earworm (heliothis) in canola, cereals, chickpeas, faba beans, lentils, linseed, safflower, vetch, field peas, lupins, maize, sweetcorn, soybeans, navy beans, mung beans, sunflower and other seed crops. Larvin® is registered for the control of heliothis (Helicoverpa armigera) in maize and sweetcorn and control of heliothis (Helicoverpa armigera and Helicoverpa punctigera) in cotton, potatoes, pulses (navy beans, soybeans, mung beans, pigeon peas, chick peas), tomatoes and tobacco. Belt ® is registered for the control of Helicoverpa spp. in a range of horticultural crops including; brassica vegetables, brassica leafy vegetables, chia, fruiting vegetables, herbs, stalk and stem vegetables and strawberries.
Cultivation at the end of the season, also known as ‘pupae busting’, disrupts the pupal stage, which can be helpful in managing CE populations. If small-medium sized larvae are present, canola can be windrowed and pulses desiccated to accelerate crop drying, which may reduce damage to seeds. Several genetically modified (GM) crop varieties produce a natural toxin targeting larvae and in these crops, CE are generally not observed to be an issue.
CE has developed resistance to several insecticides, therefore proper identification is vital when considering chemical control options. Attract and kill formulations target the moth stage and can be useful in reducing CE populations. Biopesticides have shown to be effective in crops with a narrow flowering window, such as sorghum. In cotton, growers should follow the resistance management programs available. A timely application of insecticide should be made when larvae are smaller (7 mm) and good coverage is essential for control.
Decis Options® is registered for the control of corn earworm (heliothis) in canola, cereals, chickpeas, faba beans, lentils, linseed, safflower, vetch, field peas, lupins, maize, sweetcorn, soybeans, navy beans, mung beans, sunflower and other seed crops. Larvin® is registered for the control of heliothis (Helicoverpa armigera) in maize and sweetcorn and control of heliothis (Helicoverpa armigera and Helicoverpa punctigera) in cotton, potatoes, pulses (navy beans, soybeans, mung beans, pigeon peas, chick peas), tomatoes and tobacco. Belt ® is registered for the control of Helicoverpa spp. in a range of horticultural crops including; brassica vegetables, brassica leafy vegetables, chia, fruiting vegetables, herbs, stalk and stem vegetables and strawberries.
References
Umina, P, McDonald, G and Hangartner, S (2015), ‘Corn Earworm’ South Australian Research and Development (SARDI), Cesar, Government of South Australia, PestNotes Southern, https://www.pir.sa.gov.au/__data/assets/pdf_file/0010/275824/Corn_earworm.pdf
Queensland Government (2018), ‘Helicoverpa’, https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/crop-growing/pests-field-crops/helicoverpa