INSECTICIDE STEWARDSHIP
With the growing intensity of cropping in the Riverina, the potential risks posed by crop insect pests may also rise. In turn, growers and advisors will need to maintain and expand their knowledge of insect pest management and insecticide stewardship. Insecticide stewardship considers the use of insecticides in a sustainable manner, to ultimately delay the onset of insecticide resistance. Like herbicide resistance, insecticide resistance occurs due to the repeated use of the same chemical modes of action, selecting for resistant insect pests. Examples where insecticide resistance to winter cropping pests has been detected include:
Ultimately, insecticides need to be used responsibly to delay the addition of more insecticides and insect pests to this list.
The Decision to Spray
Arguably the most important component to the responsible use of insecticides is the decision around whether to spray in the first place. To make this decision accurately, crops should be actively monitored throughout the entire growing season. This requires moving at least 50-100 metres into the paddock and looking carefully at plant parts where insects may be located (e.g. under leaves, within leaf sheaths, around developing floral structures).
Active monitoring also involves using established economic thresholds to consider the return on investment from using an insecticide. These thresholds typically describe a level of insect pressure that warrants the use of an insecticide. Fortunately, economic thresholds have been established for various insect pests and many can be found through agronomic extension platforms such as Cesar Australia. Ultimately, the decision to use an insecticide should be made only if the crop has been actively monitored and economic thresholds have been considered.
Product Choice
Another key component to the responsible use of insecticides is acknowledging the role of beneficial insects. Beneficial insects are generally considered predators of insect pests and can help to suppress insect pest numbers. It is therefore important to attempt to maintain a healthy number of beneficial insects in cropping systems. One way which growers can influence this is through product choice. Insecticide active ingredients have varying degrees of toxicity to different beneficial insects. A recent publication by Cesar Australia, summarised the toxicity of a variety of insecticides to different beneficial insect species. Some takeaways from this publication include:
Products containing a pyrethroid or organophosphate active ingredient are generally quite toxic to many beneficial insect species.
Commonly used insecticides such as Pirimicarb (e.g. Pirimor©) and Sulfoxaflor (e.g. Transform©) are generally not as toxic as pyrethroid or organophosphate products but are mortal to some beneficial insect species.
Relatively new insecticides for use in canola such as Flonicamid (MainMan©) and Afidopyropen (Versys©) are amongst the safest for beneficial insects.
Whilst a premium is typically paid for the use of more selective insecticides, these products can help reduce the likelihood of a resurgence of the target insect pest. This resurgence occurs due to the insect pest often being able to complete its lifecycle faster than its predators, resulting in an increase in the insect pest's population that is not managed by beneficial insects. Therefore, by reducing the mortality of beneficial insects in the cropping system, selective insecticides are a key component to the responsible use of insecticides.
Insecticide stewardship is an important issue that should concern every grower and advisor across an entire cropping region. The decision to spray an insecticide and the choice of product should always be given thorough consideration, to help maintain the longevity of broadacre cropping for the entire community.