11 February 2025. Paul McIntosh, Pulse Australia and WeedSmart.
Once again, I put pen to paper to explain about the phenomenon called pesticide resistance, which includes herbicide, fungicide and with emphasis this time on insecticide resistance.
Pesticide resistance is the inherited ability of a plant, insect or disease to survive and reproduce following an exposure to a dose of pesticide that would normally be lethal to a similar cohort of plants, insects or disease. A cohort of plants would mean they are of similar age of same species in a location.
However, today we talk about insects and in particular the Fall Armyworm and the Helicoverpa Armigera, which plague our broadacre crops like grain sorghum, maize and millet crops. Yes, the Helicoverpa species can also attack cotton, mungbeans, soybeans, lucerne, chickpeas, faba beans and many other grain and horticultural crops.
We, as in the royal we of broadacre agriculture, certainly learnt the hard way about insecticide resistance in the late 1980's with a group of chemistry called the synthetic pyrethroids or S.P.'s, as we colloquially call them. These are the same ones in pressure packs, that nearly every household has under the sink for flies or bugs invading our kitchen and dining room space.
Well, after the initial nearly 10 years of constant use in our paddocks against the pesky Helicoverpa larvae or grubs (and other insects like sorghum midge) in our broadacre crops listed above, the single use of this product eventually gave very poor results in those early S.P. product release days of the late 1970's and 80's. In other words, we could not control or kill the larval stage of these insects from eating our grain or fibre crops, as the 1980's decade progressed. Heliothis became the great white shark of dryland, really decimating some crops in various years.
March on to 2025 and I believe that sometimes our agricultural failures from the past, really have not been realised or valued by our current generation of farmers, agronomists and many others involved in agriculture.
Constant overuse and rate per hectare cutting or reducing is going to put enormous pressure on our current group of insecticides we use in the broadacre grain industries. By enormous pressure I mean the larvae or insect is not going to be controlled enough with these valuable, latest generation of insecticides. Yes, size does matter also for these damaging larvae with smaller grubs of less than 6 mm long being much better controlled than a 25 mm one.
My big message to all those folks cutting the rates of these new age insecticides and not rotating these mode of actions of all insecticides, is that it is very damaging to future insect control. That future is only a few years away too, if we persist in reducing insecticide rates due to cost per hectare, product availability or the very incorrect blind reasoning that 70 to 80 % control level is good enough for our larvae or grub population. We need to apply full rates of these registered insecticides against an insect population that has some unique skills of producing genetic material for future resistant bio-types.
We have learnt the hard and very visible way with huge herbicide resistance levels or folds in various plants we call weeds. Are we now going to risk a complete blow out in insecticide resistance as well by adopting poor pest control tactics? This will lead to crop infestations and damage that our limited biological insecticides, beneficial insect releases, and soft chemistry approaches are unable to control, as they can't manage the growing numbers of resistant pests harming our crops.
I summoned up plenty of background information and data from our highly regarded Aussie entomologist researchers for this article and we all agree on the tips and tactics for critical adoption of our insecticides with rotating modes of action, using full registered rates on small larvae and even to the mixing of some compatible products, like we now do so well in our herbicide war on weeds.
Once again, we can learn or adopt plenty of tips and tactics from our WeedSmart Big 6 and front and shoulders here is don't cut or reduce the label rates.
Thats all folks.
Fall armyworm destroying a cob of maize or corn on the Darling Downs 2023