Heliothis (Helicoverpa spp.) in field crops

Heliothis (now known as helicoverpa) have become very important economic pests of most crops, particularly grain legumes and oilseeds. It costs Australian agriculture $225M per annum.

The helicoverpa lifecycle consists of: moth, egg, larva and pupa. It is the larva form that causes crop damage. For more information on helicoverpa biology and ecology read the Croplink brochure "Know the enemy: heliothis biology and ecology."

Resistance in Helicoverpa spp.

We are very dependent on insecticides for the management of helicoverpa and the extensive usage of a limited group of compounds against successive pest generations has imposed severe selection pressure resulting in resistance. With continued insecticide application, the frequency of resistant individuals within a population increases, leading to field control failures.

Within our cropping systems we deal with two species of helicoverpa: Helicoverpa armigera and Helicoverpa punctigera. Helicoverpa armigera occurs on both monocots (triticale, barley, wheat, canary etc.) and dicots (chickpea, linseed, faba beans, canola, some broad leaved weeds, etc.) while H. punctigera is limited to dicots.

H. armigera and H. punctigera are both migratory. Moths are capable of flying long distances as well as moving extensively among fields within a region. H. punctigera frequently reproduce during the winter season on flowering plants within inland regions of Australia. With the onset of spring, these ensuing generations of moths often migrate to cropping areas of the eastern coast. The number of moths participating in this migration is largely determined by rainfall and the abundance of "out-back" host vegetation during the winter period.

In contrast, H. armigera tends to over-winter as pupae in the soil of late planted summer crops and therefore remains in the local area. Moth emergence from these over-wintering pupae often begins between September and October. Small numbers of H. armigera emerge in spring and often take several generations to build up to high numbers. Crop damage by H. armigera is therefore most common during the later part of the summer season.

These ecological differences are partly responsible for H. punctigera being predominantly an early summer pest and H. armigera a late summer pest. The localised activity of H. armigera within cropping regions also contributes to its ability to readily build resistance to insecticides. Without large-scale migrations of H. armigera from unsprayed areas of "outback" native vegetation that to dilute localised resistant populations, the phenomenon of insecticide resistance compounds rapidly.

H. armigera have multiple resistance to chemical groups and are more difficult to control. H. punctigera are susceptible to all current chemicals and are relatively easy to control. Spray timing is crucial to achieve satisfactory results.  

Strategies to manage resistance to insecticides

• Check that the crop is at a susceptible stage to insect damage.
• Identify which species of helicoverpa larvae you have in your crop and that they are at an appropriate size to effectively control.
• Spray only if the larvae are doing economic damage (e.g. the value of the crop saved should exceed the cost of spraying).

Insecticide resistance management strategy (IRMS)

This strategy is developed each summer in order to contain the increase in resistance of H. armigera to insecticides including pyrethroids, carbamates, organophosphates and endosulfan. In its present form it mainly applies to summer crops, especially cotton, but in coming seasons, as more insecticides are registered in grain crops, a farming systems insecticide resistance management strategy will be developed.

Currently pyrethroids can be used at any time throughout winter or summer, on any crop (except cotton) and on any insect where registered. HOWEVER, if you are targeting H. armigera larvae over 5 mm, pyrethroids provide unreliable control results.

Refer to the current Cotton Resistance Management Strategy for detailed information: available from your local DPI Cotton Industry Development Officer.

Major guidelines

1. Currently there are no restrictions on the number of pyrethroid sprays that can be applied to non-cotton crops.
2. Do not use Steward^TM against helicoverpa on chickpea after October 15^th. This cut-off date aids resistance management by allowing a full generation of helicoverpa to develop between the last use in chickpea and the first possible use in cotton.
3. It is strongly recommended that pyrethroids not be used on Helicoverpa armigera, as they are unreliable.
4. The use of ovicides may be warranted in the event of high egg pressure - use methomyl before the black head egg stage.
5. Pyrethroids should be targeted only on small larvae (less than 5 mm long) as application on larger resistant larvae will be ineffective and will increase levels of pyrethroid resistance.
6. Use recommended larval thresholds to minimise pesticide use and reduce resistance selection.
7. Avoid consecutive sprays of pyrethroids where H. armigera are emerging from neighbouring maize, sorghum or sunflower crops, as resistant levels will be exacerbated by selection of pyrethroid resistant moths prior to mating.
8. Cultivate chickpea and alternative crop residues as soon as possible after harvest to destroy pupae. Cultivation must be completed no later than one month after large larvae were observed in the field, otherwise the moths will emerge and move elsewhere.
9. Avoid using broad-spectrum sprays such as organophosphates or pyrethroids early in the season. They reduce the numbers of beneficial insects and increase the chances of aphid, mite and further helicoverpa outbreaks.
10. Do not respray an apparent failure with a product of the same chemistry.

Helicoverpa control on an area wide basis

Farmers are faced with increasing problems of controlling helicoverpa. In response to this a Helicoverpa Regional Management Strategy was formulated by producers, consultants, researchers and extension personnel and was implemented in two pilot study areas on the Darling Downs 1998 - 2001. This strategy aims to manage helicoverpa at a regional level rather than each farmer making helicoverpa control actions in isolation. This has led to a situation where every farmer is communicating and co-operating to fight the battle against helicoverpa.

The basic principles of the strategy involve a yearly cycle of management practices, which includes tactics that aim to reduce:

• The population of over-wintering helicoverpa pupae (March - June).
• The early season build-up of helicoverpa on a regional/ district scale (July - November), and
• The mid-season population pressure on helicoverpa sensitive crops (December - March).

Key components include: Crop checking, pupae busting, improved management for commercial chickpea crops, chickpea trap crop, using information from pheromone traps, realising the contribution of beneficial insects and insecticide management. Many areas outside the original pilot study areas are now implementing similar strategies. Contact your local extension officer or consultant for information on existing groups in your region, or how to form a new group. For further information on the strategy contact IPM Extension Officer at Pittsworth DPI, 07 4693 2486.

Control options

Presently there are often no available control options other than the use of chemical insecticides for helicoverpa larvae once in a crop. Spraying should be carried out promptly once the threshold for each insect has been reached.

Spray small or spray fail

Helicoverpa grow rapidly and a few days delay in spraying can result in major crop damage and increased difficulty in control. If a spray application is delayed for more than 2 days, for any reason, the crop should be rechecked and reassessed. Ensure helicoverpa larvae are at an appropriate size to control effectively. Spray only if the larvae are doing economic damage; i.e. the value of the crop saved should greatly exceed the cost of spraying.

Seek professional advice on which product is best to ensure you are NOT:

• Spraying unnecessarily (i.e. below threshold).
• Wasting money on an insecticide to which insects are resistant.
• Assisting in the development of further resistance.

Common insecticides and registered application rates can be found in crop chapters in this book. These are not complete lists of all products registered in winter crops and it is recommended that you check Infopest before applying a chemical. As always, read the label.

Due to the resistance that helicoverpa has developed to all major chemical groups, it is important to remember that recommended chemicals are not necessarily going to give adequate control in each situation. Local knowledge of which chemicals are working in a particular area should be sought from consultants and agronomists in your area.

Resistance levels to available chemicals may reduce the efficacy of insecticides.

Last reviewed 25 May 2006