Potato growers that use a “hard” pesticide-based approach to pest management that kills beneficial insects will be 100% reliant on further chemical applications.
Dr Horne provided a vivid example of the impact of killing beneficial insects in potato crops with pesticides.
“A grower we work with accidentally ordered the use of the synthetic pyrethroid insecticide Axe instead of the fungicide Ace. Recognising the smell, he called a stop to the spraying halfway through a paddock. One month after the incident, 80-100% of leaves that were sprayed had aphids, compared to less than 10% in the unsprayed area.
“The aphids were mainly being controlled by brown lacewings and parasitic wasps, but when they were disrupted there was a flare up in aphids.”
Instead of being solely reliant on chemicals, Dr Horne said that growers should base programs around biological and cultural controls that are supported by selective or compatible pesticides.
“There are a lot of beneficial insects, but they are not necessarily enough on their own. So, I am not saying don’t ever use pesticides, just use them strategically. We have some good highly selective products, so look after them with strategic use.”
Dr Horne described beneficials such as (bright red) predatory thrips, damsel bugs and hoverflies that can help to control different potato pests, and the mortality caused by different chemicals.
“Growers need to monitor for pests and then consider what beneficial species they need to look after to maximise biological control. Then, if they need to use chemicals to support control efforts, select one that minimises the impact on beneficials. Don’t just consider its efficacy against the target pest.”
Guides to relevant pesticides and beneficials are available through the Biological Research Company https://www.biologicalresearchcompany.com.au/ for an annual subscription of $79.
Cultural controls are also a vital part of the Integrated Pest Management (IPM) approach.
“For Potato Tuber Moth, soil management is vital because shallow tubers are more susceptible. Overhead irrigation also reduces detrimental soil cracking compared to furrow irrigation.”
For aphids and thrips, weed management reduces the build-up of thrips near the crop, while volunteer potatoes will flower first and attract thrips which assist viruses, so also need to be controlled. Certified seed and variety selection were also highlighted.
Dr Horne believes that 50-75% of growers were using IPM. He finished the presentation with a quote from one of them, Victorian grower Wayne Tymensen.
“Since using IPM, I have used less insecticide in the last 20 years than I would have used on a single crop before that.”
The webinar can be viewed through this link.
Images supplied by IPM Technologies.