FALSE WIREWORM: AN EMERGING PEST OF CANOLA IN SOUTHERN AUSTRALIA
Melina Miles[1] & Garrick McDonald2
1 Agriculture Victoria, Victorian Institute for Dryland Agriculture, Private Bag 260, Horsham, Victoria 3401, Australia, e-mail: Garry.McDonald@nre.vic.gov.au
2 Agriculture Victoria – Rutherglen, RMB 1145, Rutherglen, Victoria 3685, Australia,
e-mail: MilesM@prose.dpi.qld.gov.au
In recent years, false wireworms (Coleoptera: Tenebrionidae) have emerged as a significant pest during the establishment of canola seedlings in the Victorian Wimmera, the upper south east of South Australia, and southern Western Australia. Preliminary field trials have shown there are potentially effective chemical and non-chemical control options.
KEYWORDS: oil seed crops, Wimmera, establishment pests, chemical control, Tenebrionidae
Recent research has indicated that false wireworms (Coleoptera: Tenebrionidae) are significant pests during canola establishment on the grey clay soils of the Victorian Wimmera, the upper south east of South Australia, and southern Western Australia. Isopteron punctatissimus (Pascoe) is the predominant pest species in Victoria, whereas Adelium brevicorne Blessig dominates in South Australia and Western Australia. Species in the genera Pterohelaeus and Gonocephalum also occur, but their contribution to crop damage is considered to be relatively minor.
Seedling death is caused by larvae ‘ring-barking’, or completely severing, the hypocotyl. The injury to the seedlings makes them susceptible to dehydration and infection by disease. Larvae also feed on leaves in contact with the soil. Typically, crop establishment in infested paddocks is patchy; seedling establishment being most severely reduced in the more friable areas of the paddock. Losses of up to 15% of seedlings are regularly recorded.
The incidence of false wireworm is primarily associated with friable grey, self-mulching clays. However, there is anecdotal evidence that stubble retention and minimum tillage are contributing to the build up of damaging populations.
Field trials conducted in the Wimmera have shown that there are effective chemical options for false wireworm control, as well as potential non-chemical options such as increased sowing rates and compaction of the seedbed (Figure 1).
The absence of reliable sampling techniques with which to detect the presence of false wireworm larvae prior to sowing, and the desire amongst growers to minimise seedling loss, has resulted in widespread prophylactic use of chlorpyrifos (incorporated into the seed bed prior to sowing) to control false wireworm. This trend is undesirable for two key reasons: (1) There is the potential to accelerate resistance and cross resistance to organophosphate chemicals in the major invertebrate pests of crops in southern Australia; the redlegged earth mite and blue oat mite. (2) Populations of natural enemies can be significantly affected by the application of broad-spectrum insecticides early in the season.
Very little research has been conducted on false wireworms as a pest of canola in Australian cropping regions. Farmers and farmer-advisers base much of what is known on preliminary research and anecdotal observation. Fundamental tools such as sampling techniques, and economic thresholds, backed by a sound understanding of the biology and ecology of these pests, is essential to ensure they can be managed reliably.
The small size of false wireworm larvae in early autumn, prior to sowing (<5 mm), makes their detection extremely difficult. Growers are encouraged to monitor paddocks (into which canola will be sown the following season) in late winter and early spring, when larvae are fully-grown and easier to find.
Modified soil washing and flotation (Cockbill et al 1945) has proven reliable for estimating population densities for research purposes, but is unlikely to be practical for use by the canola growers as a management tool. The absence of a reliable, farmer-friendly sampling technique is currently a major barrier to the judicious chemical treatment of paddocks.
Preliminary field trials with seed baits, heat trapping and shelter traps, prior to sowing, showed no improvement in efficiency over direct soil sampling, but these options need to be investigated further.
Once reliable sampling techniques are available, it will be possible to investigate the relationship between false wireworm abundance and crop losses (economic thresholds).
Lifecycle of false wireworm in a dryland, winter-cropping environment
The biology and ecology of the key pest species is poorly understood, but is essential to interpreting the relationship between the pest and the farming system. Only through such an understanding can opportunities for manipulating the pest with both chemical and non-chemical tactics be identified, and integrated into current farming practice.
Assistance has been provided by Denis Ballinger, Darren Wrigley, Dave Robson and Bruce Holding. Field work has been undertaken with cooperation of many growers in the Wimmera. This research was supported by Agriculture Victoria’s Agriculture and Food Initiative.
REFERENCES
Cockbill, G.F., Henderson, V.E., Ross, D.M., and Stapley, J.H. 1945. Wireworm populations in relation to crop production. 1. A large-scale flotation method for extracting wireworms from soil samples and results from a survey of 600 fields. Annals of Applied Biology. 32:148-63.
[1] Current address: Queensland Department of Primary Industries, FSI, PO Box 102, Toowoomba, QLD 4350, Australia.