Knock down weeds
HERE we are again in early summer at the start of another summer cropping regime.
Once again the rainfall patterns have been very staggered and severe in places from hard-to-predict storms. So by my recollection, in the past 11 months we have had two solid significant rainfall events in general and, of course, some of our number have not even had those amounts.
These topsoil-wetting events do bring up a huge bulk of weeds as the photo shows. Small falls of rain bring up some surface-dwelling weed seeds like sowthistle (or milk thistle), however usually never in big weed numbers like above. It is a fact that good soaking rain after an extended dry time certainly brings up a plethora of weeds, both summer and winter ones.
In this photo there are volunteer wheat plants, black oats, urochloa, barnyard grass, bladder ketmia, caltrop, buckwheat, red pigweed, turnip and, of course, sowthistle. A fair selection isn’t there? And thank goodness this country was not planted to any summer crop.
It is a classic case of letting those initial weed strikes emerge after good rain and controlling them totally with appropriate knockdown products.
This use of knockdown herbicides pre-plant is good practice, instead of just leaving the weed control totally up to any pre-emergent residual herbicide applications. It is more than a numbers game of weed-seed bank levels in your paddocks, it also includes weed-seed positioning depth in the soil profile when using residual-type herbicides.
Our range of summer residual herbicides are mostly root adsorbed, apart from metolachlor, which is basically shoot adsorbed as a short description. There is an awful lot of this Group K grass herbicide being applied these days to get on top of our grass issues. I have observed through the years that grass seeds sitting on the surface are not well controlled at germination time solely by using metolachlor products.
Mind you, I have been called out to many breakouts or assumed product failures in the past 38 years that metolachlor (Dual was the original name) has been around. So these days it is more difficult to assess any product complaint with general herbicide resistance, so increasingly prevalent across all modes of action.
Not that I have been advised of any herbicide resistance levels to this handy residual summer grass product in metolachlor. However, herbicide resistance or not, having some atrazine or other root-adsorbed triazine combo product does assist in getting an increased percentage of grass control.
For example we have always recognised that our normal atrazine-only rates are not brilliant on annual grass issues in sorghum or maize paddocks. Add some metolachlor to the mix and invariably control levels increase. Two modes of action and two sites of action with some steady rain just after application onto level soil and you have a good plan for grass control.
So all the best for weed control and I realise it is only one of the many tasks you need to complete in this busy time. The spring rain has been fair, however we all need a good top up of soil moisture now for not only our thirsty crop plants but to also increase our residual herbicide weed-control activity.
SPROUTING WEEDS: A plethora of weeds in southern Queensland farming country this month.