Australia
April 3, 2017

Once in a while, someone comes along and asks a question that you have never given much consideration to.

Like, “Why does beer garden beer taste so bad?” or “Why do hotels always give away piles of stuff except for what you actually need, like a toothbrush or a razor?” and “Why do our pre-emergent herbicides last longer than our post-emergent herbicides before resistance bites”?

Sure, we had probably considered this question in the past, but many of us would have just assumed that the gene frequency for resistance to our pre-emergent herbicides was low.  

However, Gayle Somerville, who recently completed her PhD at AHRI, has looked at it in a different way and has come up with an alternative answer. She undertook detailed computer modelling to look at the population dynamics of annual ryegrass.  

She found that pre-em herbicides are slow to evolve resistance for two main reasons:

1. It’s all about numbers.  Pre-em herbicides such as trifluralin are short-lived in the soil and may only be exposed to about 20% of the total ryegrass seedbank, whereas post-em herbicides are applied later in the season and may be sprayed over 40% or more of the total seed bank.  The more weeds a herbicide is exposed to the higher the chance of resistance, and;
2. The post-em herbicide can protect the pre-em herbicides, like a double knock, killing any weeds that have survived the pre-em.

This will have major implications for our cropping future as we are now more reliant on pre-em herbicides and resistance to our post-em herbicides is becoming more common.

This research is hard to put into words, so click through to the website and take a look at the short videos that we have prepared that explain these concepts in simple terms.

Website: http://www.ahri.uwa.edu.au/

Published: April 3, 2017