Tread with caution
I WENT to a Pacific Seeds field day last week near Toowoomba to learn a bit more about their first commercial grain sorghum hybrid that has imidazolinone tolerance. It is a grain sorghum variety called Sentinel IG that is not a true GMO, but through company breeding strategies has come through the selection program with plant herbicide tolerances to this suite of herbicides we call imis. Specifically in Sentinel’s case is Intervix. These Group B imi products have been widely used in legume crops and other crops such as wheat, barley and maize, and in our fallow program. I was a strong advocate of utilising these effective herbicides with proprietary names Flame, Spinnaker, Lightning, Arsenal and Intervix to name a few, we may be more familiar with. They have done a great job for us in the past 10-20-odd years and of course with patents coming off these products, the influx of generics has reduced the price per hectare to use these pre-emergent and post-emergent-type herbicide lines more and more.
You would imagine that I would be very happy to see widespread use of these products these days and I am to a degree, but being older and wiser has taught me to be cautious, very cautious when it comes to widespread use of any herbicide these days. Andrew Short from Pacific Seeds did speak about using these group B products only once in a 12-month period, plus other key stewardship rules and that is all very correct, but in real life that is sometimes discarded in the face of forced rotational changes due to dry weather or high-end grain pricing opportunities. The key word is stewardship in that former sentence. Stewardship means all of us using this herbicide group responsibly and in an accepted sustainable farming system program. That means diversity must be a major part of your crop planning discussions.
So here we finally have what I/we have been calling for many years, in this evolution of an imi-tolerant grain sorghum variety. This will definitely give us plenty of extra post-emergent grass and broad-leaf weed control options on difficult weeds such as Johnson grass, that confound us in our grain sorghum crops.
So why am I cautious? When you have been practising weed control since Dad gave me a hoe in the 1960s, then you do build up quite a bit of knowledge of weed habits and species. So back in the mid 1990s, I was the brash, youngish fellow who said in open company at Moree, we will never get herbicide resistance in the northern region, because we have a wide selection of herbicides and mode of actions to use in our farming systems.
So how wrong was I and how did it happen? Put simply we relied on singular effective herbicides way too much. If 1.5 litres per hectare of Roundup did not kill the weed like sowthistle (milk thistle) then next time we would put two litres per hectare or more on it. We did not diversify and we did not rotate modes of action like we should have. As the price per litre of glyphosate came down our four-way mixtures fell away and we just added more glyphosate to the spray tank. It was a similar trend with the hugely decreased price structure of group As, dollars per hectare plus efficacy were the big and only drivers in those days.
So my first experience with an imi product called Pursuit was in 1991, and apart from lucerne, it was fairly damaging on many other annual grain crops in a post-emergent or in a pre-emergent sense.
What can we learn from those early days of relying on single modes of action in our spray program? Plenty, I would say, and we can learn plenty from our southern and westernfarming cousins as well, where mix and rotate and double knock are common terms in their herbicide spray language. They also talk about harvest weed seed control as a non-herbicide means of reducing weed seed banks in the paddock.
Do I like the thought of finally having a grain sorghum variety with an imi or specifically this part of the Group Bs’ tolerance?
The answer is yes, with a caution, however.
The caution comment is to warn you that we need great stewardship and strength of purpose to accompany our soon to be officially released grain sorghum variety Sentinel IG, which has this brilliant imitolerant technology as one of its traits, or more correctly, a hybrid attribute.