Trap-cropping
A fad or a useful helicoverpa management tool?
Trap cropping has been part of a Helicoverpa armigera area-wide management strategy on the Darling Downs for several years now. A number of growers in other regions have picked up the concept and are using chickpea trap crops as part of their area-wide management strategies.
Because trap cropping is one of the new tactics introduced it is important to understand the aim of trap cropping before using or assessing trap crops.
Objectives
The objective of spring trap cropping is somewhat different from that of summer trap crops. The basic aim of the two trap cropping approaches are outlined below.
Spring trap crops
Spring trap crops are designed to attract Helicoverpa armigera as they emerge from over-wintering pupae in spring. A trap crop, strategically timed to flower in the spring, can help to reduce the early season build-up of H. armigera in a district in some seasons.
The area-wide management strategy combines spring trap cropping, timely helicoverpa control in crops and pupae busting in autumn. In combination, these activities aim to reduce the size of the local helicoverpa population, thus reducing helicoverpa pressure on susceptible crops in the participating region.
This approach is used in different ways:
1. In Southern areas, where there is a high incidence of over-wintering H. armigera, an area of flowering trap crops acts to concentrate locally emerging H. armigera moths into a crop where they can be destroyed. The main period of emergence is late September through October and into early November.
2. In central Queensland there is minimal over-wintering of helicoverpa because temperatures are generally too warm to trigger diapause. Here spring trap crops are used to concentrate local H. armigera populations into areas where they can also be destroyed, at a time when there are few other hosts for the helicoverpa to infest.
Trap cropping is one of the non-chemical management options we have for helicoverpa.
Potentially, a significant reduction in the size of the helicoverpa population in spring, means a slower rate of population increase through summer.
Trap cropping is not just for cotton growers. On the Darling Downs there are grain growers also planting trap crops as part of the area-wide helicoverpa management strategy. There are benefits for all growers who grow crops susceptible to helicoverpa.
Which crop as a spring trap crop?
In several trials, chickpeas have proven to be the most effective spring trap crop. The search for an alternative to chickpea has been driven by the problems with chickpeas, most significantly the management of Ascochyta. Many crops have been assessed over the past few years - including; field pea, canary, linseed, canola, mustard, niger, early sunflowers, lentil and vetch - by Dr Richard Sequeira and Dr Paul Grundy in CQ and Dr Melina Miles on the Darling Downs. In all trials, chickpea recorded the highest number of helicoverpa larvae. However, in trials in CQ field pea have recorded higher numbers of helicoverpa eggs, with high mortality of these eggs meaning larval counts are lower than in chickpea. Some of the other crops were hosts for secondary pests such as mirids and green vegetable bug. On the eastern Downs, chickpea have proven to be agronomically robust, making them suitable for both dryland and irrigated situations. In CQ, field pea performs well agronomically. Further work may be warranted to trial later planting windows for field pea on the Downs and further south.
If planting chickpea, trials have shown that there is no significant difference between the attractiveness of kabuli and desi chickpea types as trap crops. As a result, desi varieties continue to be recommended for trap crops, with advantages over kabuli types in terms of seed cost and disease resistance.
Ascochyta management in spring trap crops
Ascochyta poses a major threat to the chickpea industry in Queensland. The management of ascochyta in spring trap crops is as important as managing the disease in commercial chickpea crops. If you are not prepared to manage ascochyta in spring trap crops, then it is probably better not to grow one.
One of the major advantages of using field pea as a spring trap crop is that ascochyta management is not an issue. Field pea is not a host of the ascochyta that infects chickpea crops.
To minimise the risk of ascochyta developing in spring trap crops it is necessary to implement the same routine of site selection, cultural control and fungicide application as you would apply in commercial chickpea crops (see the annual " Chickpea Management Strategies for the Northern Region" and the "Strategies for the control of foliar diseases in chickpeas" brochures for details).
Currently available chickpea varieties are more susceptible to ascochyta than new commercial varieties being released for southern states. It may be possible to source small quantities of seed of these aschochyta-resistant varieties, specifically for trap crops. Whilst these varieties would not be as well adapted to Queensland conditions in terms of yield potential, this is not important for trap crops. Even varieties that have greater ascochyta-resistance need to be managed to minimise the occurrence of the disease.
Importantly, consider the location of spring trap crops in relation to subsequent commercial chickpea crops - both on your farm and on neighbouring farms. It may be easier to manage rotations if spring trap crops are planted in the same field as commercial crops (the planting date of trap crops is later). This approach will simplify stubble management activities and rotations.
Remember that spring trap crops should not be planted in the same block each season. If not managed properly, spring trap crops are potentially major sources of ascochyta inoculum.
Spring trap crop options
If you want to plant a chickpea trap crop this year you should take these steps:
- For information on planting and management of spring trap crops read the "Spring Trap Crop Management Guidelines (2000)" brochure, available from DPI&F offices.
- Set aside an area to plant your trap. Consider implications for subsequent crop rotation - particularly chickpea crops.
- Buy your 'Pulse Australia Industry Recommended Seed' early to ensure stocks are available.
- Obtain a copy of the "Diseases in chickpeas" brochures. Available from your local DPI&F office
- Follow the planting recommendations in 'Spring Trap Crop Management Guidelines'. If you choose to plant field pea rather than chickpea spring trap crops, refer to the Queensland Winter Crop Management Notes (available on the DPI&F website) or information on trial results in CQ.
- Follow the disease management recommendations in the Management Guidelines.
Summer trap cropping
A summer trap crop aims to draw helicoverpa away from a susceptible crop such as cotton or mungbeans and concentrate them in another crop such as sorghum, pigeon pea or lablab. Once concentrated in the trap, the helicoverpa larvae can be rigorously controlled or the crop destroyed. In addition, some summer trap crops may produce large numbers of beneficial insects that can then move into nearby crops. For example, the parasitic wasps Trichogramma and Microplitis are often produced in large numbers in sorghum and maize. In central Queensland cotton growers are using summer trap crops of pigeon pea as part of their resistance management strategy for Bollgard®II cotton.
The summer trap cropping concept is still in a research phase and any benefits are not yet quantified. At this stage, summer trap cropping for helicoverpa (other than in central Queensland) is not being promoted by the DPI&F Entomology team as a tool for helicoverpa management.
It is thought that the diversity of the cropping system on the Darling Downs, for example, provides a 'natural' system of trap crops. An alternative approach to specifically planting summer trap crops, is to manage the current range of crops (particularly winter cereals, sorghum and maize) to act as trap or beneficial nursery crops.
Further information and access to DPI&F's information services
- DPI&F Business Information Centre: Phone 13 25 23 (Queensland residents) 8 a.m. to 6 p.m. Non-Queensland residents phone 07 3404 6999; E-mail callweb@dpi.qld.gov.au
- Current national information on agricultural chemicals registered for use on various pests is available on the Infopest CD-ROM. Write to GPO Box 46, Brisbane, Qld. 4001, or email infopest@dpi.qld.gov.au for further information. Always refer to product labels before application.
Content by Dr Melina Miles and Ms Julie Ferguson, DPI&F, Toowoomba.
Last updated January 2005
