Avoid crop competition
THE photo is of a large barnyard grass plant growing in a 2018 grain sorghum block.
There was one of these large echinochloa plants every 20 metres. Now this plant is sure to shed up to 30,000 seeds, of which even a germination viability of 30 per cent is likely to cause plenty of crop competition problems and reduced soil moisture levels over the next few years.
If this plant is Group M (glyphosate) or Group A (fop or dim) herbicide resistant, the problems become even more so in your paddocks, as it becomes more difficult to control.
Let us configure these seed numbers into the equation below with the knowledge that the progeny from these HR grass plants will be HR as well.
I have often heard it said that the most expensive herbicide application is the one that does not work and that is true. However, we still constantly apply herbicides on our weeds and many times we do so with more a hope for satisfactory control than the actual result may be.
So the scenario goes like this, that the agronomist inspects the paddock and advises the farmer to spray the entire block with one litre per hectare of glyphosate 450, plus some adjuvant. The result on two previous spray occasions in the summer fallow has been reasonable, with well over 95 per cent control on the weed spectrum, especially the barnyard grass population.
A fairly cheap spray and the paddock can be done before breakfast time. Now in that previous spray operation, the 95 per cent result was fair, however the five per cent survivors that did not die went on to set seed.
Now these few barnyard grass survivors did not die because of what reason? Did the boom kick a bit and our coverage droplets per square centimetre on the grass target was poor? Were they bigger and drier due to the density of these barnyard grass plants in various places? Or could it be a combo of all things mentioned here.
These days as soon as a plant does not die from a herbicide application, the whole world yells herbicide resistance. Yes, there is much more of this HR phenomenon around and we are all responsible for it, with the over-reliance on the weed control in a drum.
However it may not all be herbicide resistance problems. The other problems mentioned that have plagued us for years in performing boom spraying could still be the issue.
Wouldn’t it be good if you could test for herbicide resistance on your barnyard grass? Well you can. My preferred way is by using your physiologically mature seed, so therefore it takes some weeks’ duration. Proving you have herbicide resistance can give you an advantage in designing a spray program for next summer.
SPREADING ROOTS: Large barnyard grass plants growing in a 2018 grain sorghum block.