Australian Esperance recommended pesticide rotation program against resistance

With a steadily increasing level of trifluralin resistance across the Esperance Port Zone, Australia, new modes of action have been welcomed by local growers to keep older chemistries relevant.

Boxer Gold and Sakura are the latest products to enter the pre-emergent herbicide market and long-term trial data compiled by Syngenta suggests there is no statistically significant difference in efficacy between the two, however they do work differently and one aspect that is often discussed is the length of residual control.

Syngenta solutions development lead Paul Chatfield said that even if trifluralin is still effective, it is worth considering chemical rotation to minimise the risk of crop protection failing and jeopardising yield.

"A herbicide rotation program that incorporates all pre-emergent herbicide options is the most robust way to use herbicides as a tool to manage resistance," Mr Chatfield said.

He said Boxer Gold is largely more reliable in the early stages of crop establishment due to multiple sites of uptake by ryegrass through the mesocotyl and root compared to Sakura which is root only.

"In most seasons, the length of residual activity provided by Boxer Gold will be sufficient to provide effective control of ryegrass as it's active at crop establishment, when ryegrass germinations are strongest."

"Any subsequent germinations of ryegrass will be significantly less competitive as a result of the established crop being able to effectively compete for light, water and nutrients."

Ryegrass will commonly establish in Sakura-treated paddocks because of the need for the herbicide to be absorbed by the roots. While this will lead to good early control of shallow germinating weeds, deeper germinating ryegrass is likely to establish before the herbicide is washed down into the root zone.

This happens most commonly in the furrow and furrow walls, and is particularly prevalent in non-wetting sands.

Residual control is also largely dependent on the root zone staying sufficiently wet for activity over a sustained period of time.

"The benefit of long residual control must then be weighed against the nutrients and water lost by the crop due to ryegrass plants establishing before control can be achieved."