Battling spread of black oat
Herbicide resistance the challenge
.OUR summer season still has some heat in it that is for sure, and no rain as yet.
After all the recent Northern Region GRDC update discussions, I do believe many of us have little to zero subsoil moisture in our fallow blocks. This is a large concern for many reasons and of course uppermost in my professional thoughts is future weed-control options and more specifically today is the black oat, or wild oats as we also call them.
It is just another plant out of place in our winter grain crops and no doubt there are livestock owners who would be happy to see any oat plants emerge after some rain to use as fodder, as has been done in the past.
I have no idea how or when this extensive dry period will break, however if I look back over the past 40 of my agronomy years, I can recall some mighty big initial drought-breaking rains falling in autumn and early winter, which we then planted our entire winter crop on.
For instance, the large autumn break in one of those very dry periods was after the extremely cold time in the 1982 winter, followed by a very dry and hot summer until mid-April 1983. Then it started to rain for the next 14 days and we had gradual soil saturation and eventual floods after two weeks of solid rain.
I cannot recall if it was predicted, however a large area of regional Queensland and northern NSW copped a real drenching.
This was our first big rain and nobody was going to let this major rain event slip away without planting a crop, which we did of course.
Needless to say, the weeds came up in droves and one of these was black oats. This was the first major opportunity to use this expensive ($23 per litre equivalent) herbicide called Roundup as a pre-plant spray to stop transplants of weeds in the planting operation.
Our specific black oats herbicide options were not large in those days and the pre-emergent options were Avadex BW and trifluralin as a possible pre-plant incorporation combo and our stillavailable flamprop-m-methyl (Mataven) as a post-emergent in-crop spray for wheat only.
Still, we got through that very wet winter, however a lot of post-harvest seed cleaning and drying was done that year. Hoegrass was not very effective in the north for our species of black oats.
Onwards to 2019 where we have more black oat herbicide options in wheat, barley, chickpeas and faba beans, however we do have more problems in the level of black oat herbicide resistance.
The hard part is knowing or even just strongly suspecting how much black oats may emerge in our paddocks after our first major rain event and what level of group-A resistance this population may have.
The fop and dim group of herbicides (group A) have proved a revelation in controlling many grass weed species in our winter crops, however these days the reality is we may not be able to control many of these in-crop grass weeds with these products.
Fortunately there are other in-crop options using different modes of action that may or may not already have a level of resistance to them in the field.
I discussed all this with another slightly older agronomist friend in Bill this week and as we went through the options for black oat control in our future winter crops, we realised that the old days were much easier and herbicide resistance is here to stay.
Of course, with any talk I deliver these days I am always pointing out to use diversity in your herbicide options and employ extra cultural controls like reducing row spacing, increasing seeding levels and ensuring no survivors from any herbicide spray.
From the planting of clean seed to a clean harvest operation, you will need to examine your effective herbicide alternatives, and never forget “diversity” in all your weed-control options.