WEEDS, PESTS & DISEASES No. 87 March 2010

Arable IPM-Making the Most of Beneficial Predators

Key Points • Integrated Pest Management (IPM) offers an opportunity to move away from the routine broad-

spectrum insecticide-based approach to pest management. It combines biological (natural predators), chemical (selective) and cultural controls in an integrated way.

• There was no difference in yields or BYDV incidence over two growing seasons for paddocks using IPM and conventional pest management.

• IPM managed cereals used at least one less insecticide then conventionally managed cereals. • Gross margins were slightly higher for the IPM sites. • There are a wide range of beneficial insect predators that can contribute to pest control. • The numbers of resident predator beetles were a lot more abundant at the IPM managed sites.

Introduction Prophylactic use of pesticides has lead to the ‘pesticide treadmill’ where the loss of beneficial insects can lead to pest outbreaks, which can lead to increased use of insecticides. This can result in pests developing resistance to insecticides. Integrated Pest Management (IPM) offers an opportunity to move away from the routine broad-spectrum insecticide-based approach to pest management. It is an approach to pest control that aims to maximise the use of beneficial insects whilst minimising unnecessary pesticide use. This is done by combining biological (natural predators and parasites), chemical (selective molluscicides & pesticides) and cultural controls in an integrated way. A three year project, supported by FAR and MAF SFF, aimed to develop and demonstrate IPM strategies for arable crops. To build farmer confidence the relative merits of IPM and conventional systems (financial and environmental) were demonstrated. This was done using paired paddock comparisons where the IPM and conventional (current farmer practice) pest management systems were compared side by side. Data was collected to establish presence and abundance of key pests (slugs, aphids, viruses) and beneficial predators. Financial validations were also completed for both the conventional and IPM systems. Beneficials There is a wide variety of beneficial predators that contribute to pest control in crops. Some are resident predators that live in the crop all year round such as native carabid beetles (Figure 1). These are generalist feeders that predate on pests such as slugs and aphids. Other beneficial insects are transient and may only arrive in a crop if there is a pest present to sustain them. Aphids are a key food source for a large number of insects, for example, hoverflys and ladybirds tend to only lay eggs where there are aphids present. Both the larvae of hoverfly’s (Figure 2) and ladybird’s (Figure 3) are dependent largely on aphids. Both the adults and larvae of brown lacewings (Figure 4) prey upon a wide variety of small insects including psyllids, thrips, aphids and small caterpillars. Other beneficial insects are more species specific such as parasitic wasps (Figure 2).

The females use their ovipositor to place eggs on or inside another insect. When the wasp larva hatches from the egg, it feeds on its host and eventually an adult parasitic wasp emerges. There are parasitic wasps associated with many pests such as leaf miner larvae, cabbage white and diamond back moth caterpillars and aphids. Aphid parasitic wasps actively search for aphids which once parasitised will turn a dull brown. When the wasp emerges it leaves behind an aphid shell with a circular hole (Figure 5). Results IPM deals with all pests whereas chemical control targeted at one pest can interfere with biological control of other pests. For the IPM sites broad-spectrum insecticides were avoided and all management decisions were based on monitoring. Thresholds don’t necessarily provide correct information because everything is relative to presence and abundance of beneficials. The IPM strategy for the autumn sown wheat paddocks was:

Slugs were monitored during crop establishment and if bait was required broad spectrum molluscicides were avoided. This is because baits such as Mesurol® will kill beetles through secondary poisoning (beetles are poisoned after eating a slug that has ingested bait). EDTA baits such as Multiguard® or metaldehyde baits such as Metarex were recommended instead. Because the cereal aphid is responsible for transmitting BYDV, seed was Gaucho® treated to minimise virus spread through until the start of tillering (GS21). Plants are thought to be at risk through until GS31 so this window was closely monitored for aphids. Pirimor (a selective aphicide) was recommended if within crop monitoring deemed follow up sprays necessary. For Pirimor® to work effectively it was recommended to be applied in the morning of a sunny day. No applications of synthetic pyrethroids such as Karate® were used as synthetic pyrethroids can kill beneficial predators if timing of application coincides with activity.

Figure 1. Native carabid beetle

Figure 2. Hoverfly larva and aphid parasitoid

Figure 3. Ladybird larva

Figure 4. Adult brown lacewing and larva

Figure 5. Aphid shell left behind after parasitic wasp has emerged

Figures 6 shows slug and beetle averages in the cereal paddocks monitored for both the IPM and conventionally managed sites (seven paddocks over 2 years). The use of synthetic pyrethroids on the conventional sites has resulted in fewer beetle numbers compared to the IPM sites.

Figure 6. Average slug and beetle numbers in seven cereal crops BYDV assessments were carried out at the flag leaf stage to determine if there were any differences in BYDV incidence between the conventionally and IPM-managed sites for both the 08-09 and 09-10 growing seasons. The BYDV assessment found there to be negligible BYDV at all sites for both seasons. Aphid monitoring determined that 08-09 was a low risk year whereas the 09-10 growing season started out as high risk and then progressed to low risk throughout the season. There were negligible yield differences between the IPM and conventionally managed sites. Gross margin analysis was completed by the Agribusiness and Economics Research Unit at Lincoln University and was marginally higher for IPM sites. Conclusions The farmers involved in this project have now become enthusiastic users of the IPM system. Their confidence in using and accepting IPM as a feasible option for pest control resulted from:

1. Demonstrable benefits of ecosystems services through reduced insecticide use.

2. Confidence in their ability to monitor insects in their crops and interpret this information due to training and support from IPM experts.

One of the South Canterbury farmers involved in the trial had a history of slug problems. He found “they were difficult to control, even with slug bait.” He discovered there were carabid beetle species present in his paddocks and he learned that some of the more aggressive insecticides being used to control the slugs were killing these beetles through secondary poisoning. After applying an IPM approach for two years, “we found that later on in the winter, when the wheat was most susceptible to slug damage, when we lifted a clod to look for the slug there was a beetle there!”

Other agricultural sector IPM adoption experiences (in NZ and overseas) have all shown that the successful widespread conversion to IPM requires a carefully monitored and supported transitional phase. Future projects will aim to provide required training to both farmers’ agricultural service providers to meet ongoing IPM needs. Acknowledgements: FAR would like to thank all of the farmers that have been involved in the Arable IPM project. ©This publication is copyright to the Foundation for Arable Research and may not be reproduced or copied in any form whatsoever without their written permission. This Arable Extra is intended to provide accurate and adequate information relating to the subject matters contained in it. It has been prepared and made available to all persons and entities strictly on the basis that FAR, its researchers and authors are fully excluded from any liability for damages arising out of any reliance in part or in full upon any of the information for any purpose. No endorsement of named products is intended nor is any criticism of other alternative, but unnamed product.