First case of glufosinate resistance recorded

Goosegrass in the foreground has not been controlled by glufosinateThe first weed species to develop resistance to the non-selective herbicide glufosinate has been recorded by researchers in Malaysia.

Preliminary experiments have confirmed concerns that an aggressive grass weed is developing populations which are no longer controlled by glufosinate.

Weed scientists from the University of Malaya have been investigating reports of weed control problems in an oil palm nursery in the state of Pahang. The weed in question is goosegrass (Eleusine indica), a globally important weed of many warm climate crops.

In Malaysia it is a particularly serious problem in oil palm and rubber plantations, and on smallholdings growing fruit and vegetables.

Goosegrass has already developed resistance to several herbicide modes of action (MOA) in a number of countries around the world. It was the second weed species to be recorded as becoming resistant to glyphosate, also in Malaysia1. To keep weed resistance at bay, and avert the threat it poses to food production, it is vital to use integrated weed management practices. These involve using herbicides with different MOA. Like paraquat and glyphosate, glufosinate has a very distinctive MOA. However, as experience with glyphosate has shown, intensive use of a single MOA herbicide regime will ultimately result in weeds becoming resistant.

To confirm that a herbicide resistant strain has evolved, it must be conclusively demonstrated that the weed population cannot be controlled by the herbicide at the normal recommended application rate. The researchers conducted experiments with glufosinate on goosegrass plants in the affected field. Greenhouse studies were also conducted to compare the response of plants from the suspect population to ones collected from an urban area with no history of herbicide application. Using a range of dose rates enables the factor by which populations differ in their susceptibility to be calculated. Rates from normal to eight times greater were selected.

Control of goosegrass populations by glufosinate (990 g/ha|) over four weeksThe results showed that a normal rate of glufosinate gave an acceptable level of goosegrass control over a four week period when a susceptible population was tested.

However, the suspected resistant population was much less affected. Not only was control after one week around half that normally expected, but the weeds rapidly grew away again so that there was little effect after four weeks.

A detailed analysis of the dose response work showed that the suspect population required more than seven times the normal dose of glufosinate to achieve just 50% control.

No new herbicide modes of action have been commercialised for over 20 years, so it is vital to keep those presently available to farmers controlling weeds effectively. Weed resistance to glufosinate as well as glyphosate deals a further blow to weed control options. Paraquat now has an even more important role to play in the rotational use of herbicides.

References

  1. Lee L J & Ngim J (2000). A first report of glyphosate-resistant goosegrass (Eleusine indica (L) Gaertn) in Malaysia. Pest Management Science, 56, 336-339