I INTEND to be very specific this week on the question of grass weeds in winter cereal crops and an old control method.
We all hate weeds or plants out of place, which are expensive to control, not just by your favourite herbicide, however also for the time taken to perform this elimination operation.
Of course when you have black oats, then putting up with a few infestations due to other more important issues gives it a platform to explode in winter cereal paddocks.
Right now for those of us that had this early April rainfall event, we are tackling heaps of slow-to-emerge summer and winter weeds and, unfortunately, some of these are not able to be controlled.
For example, early oats or barley crops with heaps of urachloa, barnyard and feathertop Rhodes in them.
So what could happen with our black oats, which is due to make its presence felt by having this large seed bank in the soil from previous years and perhaps germinating this winter?
Our rotations have sort of fallen in a heap and many decisions to plant what and where will be made on financial decisions and planting time moisture levels.
There have been plenty of mechanical operations occurring right through our farming belt and it's these blocks that we can use an old favourite black oat control herbicide in Avadex BW.
We all have our eyes on the nematode and crown rot issues and this is excellent, however you need to be wary of wheat or barley monoculture with black oats as the bogey man.
It has been proven high densities of black oats at say 100 plants per square metre and a wheat crop density of 25 per square metre, results in yield losses of 40-50 %.
If you left the weed pressure where it was and increased the wheat plants per square metre, then yield losses may be down to 10-25%.
There is one other slice of information you should consider, which is the timing and species of black oats as well. I could mention Avena Sterillis germinating and emerging in much higher numbers than Avena Fatua at soil temps below 10 degrees Celcius. I could also mention that this species property is reversed when temps are above 20 degrees.
This is further complicated by moisture requirements, with Sterillis enjoying low moisture situations, whereas Fatua is heavily present in abundant moisture situations.
What can you do?
A combination of things really. I mentioned Avadex earlier in the column and its mode of action under moist conditions is through the grass weed shoot as it moves through the top soil.
Avadex also only lasts for 6-8 weeks under moisture and does not like lumpy soils or more than 30 % stubble cover interfering with its mode of action.
It also needs incorporation into the top two inches of soil within four hours of application.
Is it compatible with other herbicides and the good news is that Glean, Trifluralin and Gramoxone are all compatible with this old product and all are worthy of use consideration.
It all seems a lot of bother when all we need to do is put a fop or a dim in crop on barley or wheat to control these troublesome black oats.
We should be following this spray regime in summer with a Gramoxone double knock.