HERBICIDE-resistant weeds are becoming more and more of a problem each year. They harbour what is known as ALS resistance.
In such cases, acetolactate synthase is inhibited in the plant cell and the weed cannot be controlled by sulfonylurea- type (SU) products such as Ally, Cameo, Harmony, Calibre and Boxer.
How do I know and can I recognise resistant weeds on my farm?
If a weed is totally ALS resistant, then no matter how much or how often SU is applied it will not control the weed.
If you suspect your farm has resistant weeds, then check fields weekly after a normal herbicide application.
Place a marker in an area of the field where the suspect weeds grow so you can revisit the same spot each time.
Where the herbicide has killed the majority of weeds but left corn marigold, or perhaps killed only some of the corn marigold (in the same area), resistance is very likely.
In the southeast, ALS herbicide-resistant corn marigold is becoming very common.
Control of resistant marigold is difficult, but the addition of Galaxy, usually at the full rate of 1.5l/ha, or a HBN such as Stellox at 0.75l/ha, are worthwhile options. ALS resistant chickweed is generally more widespread around the country. It is easily controlled with the addition of CMPP or Fluroxpyr to SU herbicides.