30 April 2024. Last updated 30 April 2024.
Macca’s Musings – by Paul McIntosh (Pulse Australia/WeedSmart)
I am continually advised that many of our export grain sorghum customers are not happy with the amount of admix or other seeds like Johnson Grass that is present in our overseas boatloads.
Now for some end point uses by these significant grain customers, there is no issue for non-grain sorghum seeds type presence, however for many other users, it is a big problem and makes our marketing options and price offered more at risk. It certainly constrains the dual use option ability, when accepted by the export buyer.
A reasonable solution for in-crop Johnson grass (J.G.) plants is if you have an Imi tolerant grain sorghum variety and apply a selective herbicide like Intervix. Now Intervix is not going to totally control those big old Johnson grass plants, however for those less than 6-inch-high seedlings, it will do a reasonable control job. Those larger plants really need control measures applied well before planting your grain sorghum crops and early in the fallow period.
There are a few tricks to consider when devising a plan to rid your cultivation blocks of this handy livestock fodder.
Now like most perennials, good old Johnson grass can develop a big rhizome root system well away from its initial germination point. Frequently, I have found JG roots well over 3 mts away and they can cover the entire plant's below ground 360 degree circumference.
Unfortunately, even when you apply a robust rate of Glyphosate in the best preferred autumn timing, the huge root system is invariably not allowing the herbicide to be fully translocated to the end points of these roots. So, you end up with a half dying plant out of place that eventually regrows. Not necessarily herbicide resistant, however certainly needs a plan of attack to get on top of the original mother plant and the seed bank levels.
You really need to break up these larger root systems with a tyned implement, so that each new section of root can develop its own above-ground leaves and stalk section. This allows future herbicide applications to be able to move entirely through the leaves and stalks and into the shortened root system.
As usual, some weeds like our perennial ones, need a management plan with some mechanical intervention initially, for our herbicides to be more effective. Johnson grass or even couch are two of them.
Nut grass, on the other hand, needs less or nil tyned cultivation events and more strategic herbicide applications to get it under control and out of our paddocks.
That’s all folks.
Johnson Grass in a paddock of Grain Sorghum on the Darling Downs.