Pest study producing results

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A trial of integrated pest management (IPM) strategies in forage brassica crops has shown positive signs.
The first year of a three-year evaluation conducted by Plant & Food Research, as part of a Ministry for Primary Industries (MPI) Sustainable Farming Fund project titled ‘‘IPM strategy development and demonstration for forage and seed brassicas’’ has produced some pleasing early results.
An IPM approach to pest control utilises beneficial insects (such as natural predators and parasitoids), cultural controls (such as management methods) and, when necessary, selective insecticides to control pests in target crops. IPM has been used successfully in the New Zealand horticultural industry for many seasons.
The study aims to look at the benefits of an IPM programme in brassica crops compared with the traditional broadspectrum insecticide approach.
Broad-spectrum insecticides will have an effect on both target pests and beneficial insects, so this approach can lead to spikes in populations of unwanted insects at various parts of the season.
An IPM programme utilises chemistry such as DuPontTM Exirel® insecticide, which selectively targets pests such as cabbage white butterfly (Pieris rapae), diamondback moth (Plutella xylostella), soybean looper (Thysanoplusia orichalcea), European leaf miner (Scaptomyza flava) and grey cabbage aphid (Brevicoryne brassica).
It also leaves key beneficial insects in the crop which are then able to continue to work and help control pests that reappear in the brassica crops.
In trials conducted in the Canterbury region inforage and seed brassica crops, the farmer’s standard programme was compared alongside an IPM strategy. In all sites predators such as lacewings and ladybirds were active, although it was the parasitic wasps that seemed to have thebiggest impact on reducing both aphid and diamondback moth pressure.
Results of the first year highlighted the importance of relying on predators and parasitoids inconjunction with selective products from chemical companies for an overall IPM strategy.
Feedback from farmers who had participated in the first year was generally positive, with a greater understanding of the role beneficial insects can play in the brassica production system.
Results from the year demonstrated an IPM approach could provide as effective control of pests as the conventional approach, while using fewer insecticides.
It was noted that the arrival of pests such as diamondback moth into a crop was generally followed by parasitic wasps, and the use of an insecticide such as Exirel® could assist in controlling the pests while beneficial numbers were increasing.
At an irrigated kale paddock on a sheep and beef farm, diamondback moth caterpillars were present at the beginning of December. Numbers continued to build and at the end of December the broad spectrum insecticide Lorsban was applied to the conventional side and a selective Bt(Bacillus thuringiensis) insecticide was applied to the IPM side.
Caterpillar numbers declined on the conventional side and, after a small decline of the IPM side and some feeding damage, a decision was made to apply Exirel® insecticide across the whole paddock on January 9.
On the IPM side, as a result of the Bt spray, high rates of parasitism developed and the reduction in caterpillars from the Exirel® insecticide in combination with the ongoing presence of the parasitic wasps meant that good control was maintained for the rest of the season.
High rates of parasitism were noted on the caterpillars in the weeks that followed and numbers remained similarly low across the whole paddock from mid-February onwards.
The additional spray of Ampligo insecticide on February 18 on the conventional side did not visibly alter the diamondback moth abundance compared to that on the IPM side where parasitic wasps were controlling the caterpillars.
Aphids were not found in the crop until mid-January, but the numbers did not build too rapidly (possibly because there were already lacewings and other predators present in the crop).
A month later, aphid-associated parasitic wasps were present and these maintained a good degree of control for the rest of the crop.
The project will continue through to June 2017 and examine yield results and gross margins as part of that process. It is hoped the expansion of IPM systems could significantly improve the financial and environmental performance of these crops. There is growing interest from farmers wanting to adopt new pest management practices and agronomists wanting to offer a wider range of services to their clients.
The Forage Brassica IPM development project is funded by MPI, DairyNZ, Forage Innovations Ltd, DuPont (New Zealand) Ltd and the Foundation for Arable Research.