Bug allies can help cut chemical costs
Not all insects in crops are pests. Fiona Conroy reports on the IPM approach, which seeks to enlist the good agains the bad
[Photo: Monitoring progress: Mark Jordan-Hill inspects a canola crop at "Mt Hesse" in Victoria, which is part of the IPM pilot. Photo by Fiona Conroy.]
An alternative approach to controlling insect pests in high rainfall zone broadacre crops has the potential to save growers thousands of dollars in reduced insecticide use, slow the development of resistant insects and benefit the environment, say its promoters.
A pilot program is investigating the potential of using integrated pest management (IPM) strategies to reduce the reliance on pesticides to control insects, such as slugs and aphids.
The program is enlisting the help of IPM Technologies to monitor crops on a number of properties between Geelong, the Grampians and south of Ballarat in western Victoria"s expanding grainbelt. Most of the growers involved in the IPM pilot are members of Southern Farming Systems and keen to try the IPM approach
.Dr Paul Horne and Jessica Page, of IPM Technologies, regularly monitor a number of paddocks and crops on each of the properties with the aim of developing pest control strategies more commonly associated with high-value horticultural crops.
"Resistance is the main reason why integrated pest management has been developed," Dr Horne says. "IPM isn"t about not spraying - it"s about using chemicals wisely, combined with biological and cultural approaches to controlling pests.
"We"ve worked mainly with horticultural crops where there is a greater use of insecticides to ensure an unblemished product. The greater use of insecticides in crops such as vegetables has resulted in resistance developing relatively quickly."
Dr Horne says resistant pests which develop in horticultural crops are not confined to horticulture and have the potential to spread over districts and attack broadacre crops. In this scenario, pests like insecticide-resistant diamondback moth can suddenly become a major problem.
"If we want to look at a worst-case scenario for the future, then we can just look at what is happening in certain horticultural crops, where growers are spraying twice a week," he says. "If we want to avoid this situation developing, then we need to act now."
One of the keys to IPM is to recognise that not all insects in crops are pests, Dr Horne says. Crops can contain beneficial predators such as ladybirds, damsel bugs, lacewings, predatory mites, wasps, native earwigs and beetles, which are predators for pests such as slugs, caterpillars and mites.
"You don"t need to buy these beneficial insects. The key is not to kill what is already there, and integrate them into your overall pest strategy," he says. "Some insecticides can actually make a pest problem worse by wiping out beneficial insects as well as the pests, or by targeting the wrong pest species."
Dr Horne says the key elements in IPM are:
Monitoring is a key factor in deciding what, or what not, to do. This involves checking a crop weekly or fortnightly for pests and beneficial insects, and then judging the likely problem and the potential for damage.
"Some canola crops have a problem with red-legged earth mite while others have a mix of red-legged earth mite and blue oat mites," Dr Horne says. "Knocking out the red-legged earth mite often results in an explosion of blue oat mite numbers.
"When we use insecticides, we need to understand a product"s impact on the beneficial insects as well as the effect on the pests. It"s important to not just select an insecticide because it"s the cheapest. We need to look at its selectivity.
"Management practices used in IPM include weed management, variety selection and the location and sequence of planting.
In one Southern Farming Systems case study, a grower"s concern about his increasing reliance on pesticides triggered an interest in the potential for IPM. Mark Jordan-Hill, who runs "Mt Hesse" at Winchelsea in western Victoria, said he was prompted to rethink pesticide use following disappointing results in controlling red-legged earth mite in lucerne.
The 3550-hectare property has about 1000ha under canola, wheat, barley and field peas, and is one of a group of cropping properties piloting a crop-monitoring program as part of the IPM project."We had a mite problem in lucerne but found spraying only seemed to make the problem worse," Mr Jordan-Hill says.
"We stopped spraying for red-legged earth mite two years ago and are not getting the explosion in mite numbers like we used to. It appears we have an equilibrium with our pests and beneficial insects which is keeping the mites under a reasonable level of control."
Paddocks of canola, wheat and barley at "Mt Hesse" are being monitored weekly by Dr Horne, who has set traps and tiles to assess what pests and predators are present.
"Once we get a picture of what"s present we can build an IPM program to control the pests," Mr Jordan-Hill says. "One of our aims is to reduce our total pesticide use by using more effective pesticides which are selective and kill the pests but don"t wipe out the predators.
"In the past, we may have been effectively killing everything."
Mr Jordan-Hill says he has no hesitation in using pesticides but wants to make informed decisions about what insecticides to use and when to spray: "To date some of the paddocks in the program have been sprayed to control cutworm, while other paddocks have been left unsprayed, based on the monitoring results.
"Our main pest in canola has been slugs, while other crops have had problems with diamondback moths. We"re also conscious of aphids because of their ability to carry disease.
"You only have to look at what is happening in horticultural crops, where resistance is developing rapidly and creating all sorts of management issues. IPM gives us a chance to take their experiences on board and act before we start getting into a mess. Over three years we hope to build up an IPM system for our broadacre cropping and then take what we learnt over the three trial paddocks and apply the same approach across the whole farm."
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