‘Kilmarnock’ co-owner Andrew Watson is a staunch advocate of IPM and working with nature. Photo: Melanie Jenson

Dedication to integrated pest management (IPM) is not just a philosophical choice but a practical strategy honed over 2 decades of farming by NSW grower Andrew Watson.

Andrew and his wife Heike operate a mixed farming enterprise across 3600 ha at
‘Kilmarnock’, ‘Merriendi’ and ‘Fairfield’, to the east, north and south-west of Boggabri in north-west NSW.

They grow irrigated and dryland winter and summer crops and run a beef grazing operation in a cooperative arrangement with other local farmers.

This includes rotational grazing a herd of mainly black baldy cows on 700 ha of native and improved pastures. Cotton is the couple’s biggest crop by value, followed by maize, sorghum, canola, mustard, durum wheat and the occasional crop of chickpeas.

Andrew says the lessons learned from growing cotton have profoundly shaped his approach to grain production, particularly with regards to IPM and disease management.

His parents, John and Robyn, bought ‘Kilmarnock’ in 1965, introducing cotton to the region in 1980. They were early adopters of IPM to improve on-farm biodiversity.

They began with stabilising and revegetating the banks of the Namoi River, and planted thousands of trees to serve double duty: as wildlife corridors and to provide spray drift barriers.

Embracing biocontrols

Andrew and Heike, who took over in 2007, share that vision, aiming to minimise environmental impacts while farming sustainably and profitably.

Harvesting maize at ‘Kilmarnock’, near Boggabri. Photos supplied

Keen to further reduce insecticide use, Andrew has conducted trials to compare the impact of spraying versus not spraying on the numbers of pest and beneficial insects in cotton, as well as their effect on yields.

Andrew has also been involved in research investigating bird and microbat numbers and their role as natural pest controllers.

During a visit to the US in 2019, he met Parabug co-founders Chandler and Jaclyn Bennett and learned more about using drones to release beneficial insects.

Since then, he has contracted Parabug Australia to drop a range of ‘good’ bugs first on cotton, and then on canola, maize and wheat crops.

“There had been people who were trialling it before us, and most notably my agronomist, who also has his own farm, was advising clients to do this in the 2 years before we started,” he says.

“It was something that appealed to us. It was a matter of finding the contacts and having a bit of belief in it, because 2 months ahead of when you think a pest is going to be a pest, you’ve got to make the decision to spend the money.

“It certainly appeals to our sense of the way we want to run IPM on this farm, and how I feel everyone should be trying to run IPM to work with nature.”

Beneficials as insurance

Drawing on research by commercial suppliers of beneficial insects, Andrew says they’ve been able to strategically target a range of pests.

They deploy the parasitic wasp Eretmocerus hayati against silverleaf white fly in cotton, Phytoseiulus persimilis mites to control spider mite in maize and cotton, and Aphidius colemani wasps for aphids in canola and wheat.

It can be tricky staying on top of pests such as mites and aphids that can move from one crop to another, but the strategy has proved effective.

“Every time we’ve made a release for a particular pest, we haven’t had to spray, while about 60% of the time my neighbours have,” Andrew says.

He estimates 40% of the time he might not have needed to release beneficial insects because there was enough natural control present, or the season did not favour the pest, but he still regards such releases as a valuable insurance policy. The bigger question is cost.

The insects can be relatively cheap at $24.20 to $35.20 per pack of 500 Aphidius colemani wasp pupae, $70.95 for a 10-pack of vials each containing 500 Eretmocerus hayati wasps, or $41.25 to $113.20 for packs of 2,000 to 10,000 Phytoseiulus persimilis mites. The main expense, says Andrew, is hiring a licensed drone operator to disperse them over large areas. This costs from $10/ha to $15/ha.

Compared with the cost of conventional chemical control, Andrew says insect releases cost the same or up to 50% more, but have the additional benefit of avoiding the treadmill of repeated sprays and the risk of causing flare-ups of other pests.

“Our goal, however, is not to end up having to do 3 or 4 expensive sprays down the track.”

Harvesting sorghum at ‘Kilmarnock’, near Boggabri.

Drone delivery

Key to the program’s success is an efficient and even distribution of the beneficial insects at the right time.

A drone is fitted with a tube filled with a carrying medium, such as vermiculite or rice hulls, and insect eggs or pupae on the verge of hatching.

As the drone flies, the tube rotates and its contents fall through holes onto the crop or the ground.

Efficient and even distribution of beneficial insects at the right time by drone is key to the success of the Watsons’ IPM program.

Surprisingly small quantities are needed, with as few as 2 vials enough to treat 400 ha of cotton or grain crops.

In the first year, Andrew says they laid a tarp on the ground and, after a pass with the drone, later found crawling insects on it, reassuring him the bugs were able to survive the drop.

Timing depends on the type of insect to be dispersed.

Wasps, which are highly mobile once they reach the adult stage, can be released when crops are fairly small.

On the other hand, application of crawling insects, such as mites, at higher concentrations is deferred until the leaves of crops such as maize are touching across the row, which sets up a favourable microclimate and allows them to crawl from plant to plant.

“We don’t try and control the pest when it’s at its maximum and doing all the damage,” says Andrew.

“We go in before and put out a limited number of beneficials so their populations grow with the pest populations.”

The Watsons also manage tree lines and riparian environments to maintain a bank of beneficial insects.

Rotation, tillage and disease management

Beyond IPM, Andrew emphasises the importance of crop rotation and tillage practices for managing soil-borne diseases, such as crown rot in cereals, Sclerotinia and blackleg in canola, and black root rot and Verticillium wilt in cotton.

The farms are mostly controlled-traffic, based on 2 m wheel centres and 12 m widths for the 12 m planter, 24 m spreader and 36 m sprayer in both irrigated and dryland crops.

This reduces soil compaction and promotes healthier soil structure. Deep tillage during preparation for cotton and maize crops removes nutrient layering and is also used to incorporate chicken manure and other fertilisers to depth.

Soil types are mostly brown chocolate vertosols, with some harder-setting red loams across the floodplains adjacent to the Namoi River. The northernmost farm, ‘Merriendi’, has some alluvial gravel, and the dryland farm, ‘Fairfield’, has undulating clay soils.

Soil pH on the irrigation farms, ‘Kilmarnock’ and ‘Merriendi’, is 7.5 to 8, regardless of soil type. Soil testing is being carried out at Fairfield, which the Watsons acquired recently.

Average annual rainfall is 593 mm and, over the past 20 years, “immensely variable”, ranging from 220 mm to more than 1000 mm.

Rainfall is supplemented by furrow and overhead irrigation, using lateral and pivot irrigators, to apply water sourced from the Namoi River and several bores.

Cotton is the business’s “pillar crop”, providing the highest return per megalitre per hectare. It is grown every 3 or 4 years. The frequency of other crops in the intervening period depends on water availability and may include a short or long fallow, durum wheat, canola or maize.

Dryland rotations are “a little bit simpler”, typically including durum wheat, back-to-back canola, followed by durum wheat and cotton, and occasionally chickpeas or sorghum.

More recently, Andrew has embraced DNA testing of soil samples to better understand the impact of different crop types on soil diseases.

This article appeared in GroundCover