Over the decades I have been in a fair few farming paddocks and many times have I heard a farmer say to me “I have the weediest farm in the area and they are hard to kill, also.”
I would politely disavow this thought and say “I have seen much worse” – which I probably had.
The second part of “hard to kill” however may have more truth to it, given our more recent revelations and research showing that pollen from a herbicide-resistant plant can travel some distance on the wind.
My weed scientist colleagues in Western Australia demonstrated that resistance genes in annual ryegrass pollen travelled three kilometres on the wind to pollinate a susceptible plant, which then produced viable ryegrass seeds that were resistant to an ALS herbicide mode of action.
The only bit of good news here is that these susceptible plants produced fewer seeds as the separation distance increased.
Back to the bad news, and unfortunately pollinator insects like bees can also transfer pollen with resistance genes in it to susceptible plants.
Generally I have always said that bees have a roving radius from the mother hive of around three miles; however, as we have learned from major bee deaths in ag areas, when bees are hungry and thirsty, they can travel up to five miles.
Pollen grains come in various sizes too – so the heavier they are, the less distance winds may move them. Pollen viability can also be affected by air temperatures and humidity.
Concerning barnyard grass you will be pleased to know that, as it is a highly self-pollinating species, the level of resistance spread by pollen would be much lower than another local outcrossing species like pigweed.
That dratted feathertop rhodes grass is both self-pollinating and cross-pollinating, so pollen can certainly be transmitted between FTR plants.
Resistance genes can travel a long way in pollen, so critiquing yourself or your neighbours for weed burden or resistance levels could have some credit. However, it is really best to focus on the existing weeds in your own property area. Don’t forget those stock routes and roadside table drains, where weeds may grow and seed very freely and prolifically.
In our Weedsmart ‘Big 6’ tips and tactics for combatting herbicide resistance, we make a key point to advise stopping any weed from setting seed.
I call all these weed control efforts ‘Area Wide Management of Weeds’. Don’t forget to bring your neighbours along for the ‘Weed Free Area’ award that I will deliver one day!
