Friday, 1 November 2013

Fighting the resistance.

Many target species are becoming resistant to sprays
I'm sure you have heard radio reports on how a wide range of antibiotics are not working as well as they used to and have also seen exaggerated tabloid headlines stating that “giant rats resistant to all poisons are roaming our streets”  - strange how they are always giant ones isn't it?

Increasingly, resistance build up to a number of important agricultural pesticides is also causing alarm within farming circles, as Steve Foster from at Rothamsted Research points out. He's been studying the peach-potato aphid and the grain aphid - the former has now developed resistance to many insecticides including pyrethroids, carbamates and organophosphates.

"Peach-potato aphid is the number one aphid pest in the UK and many parts of the world," he says. "Some have several types of resistance and there are cases when you just can't kill them with the compounds available," he adds.
It’s not just insecticides that are causing concern, with resistant blackgrass continually dominating the farming press, as its control can cost growers up to £100/ha in some cases, rendering fields unprofitable for growing a cereal crop. Resistance is also spreading across the country as highlighted by a survey that showed amongst the 20,000 farms known to use herbicides to control blackgrass, it now is estimated that 80% or more of those will have some level of resistance to at least one herbicide.
What is more, it’s not just grasses such as Blackgrass causing problems. Plants such as poppies, mayweed and chickweed are also posing an emerging threat, with reports of herbicide resistance in chickweed in the north of England and throughout Scotland  becoming more common.
Glyphosate (you may know it as Roundup or Tumbleweed) is a product that is used by just about every non organic farmer in the country and thus it would leave a particularly large hole if weeds became resistant to this particular chemical.  Paul Neve, an assistant professor at Warwick University, is working with PhD student Laura Davies to examine whether glyphosate resistance is likely to be seen in the UK. While he doesn't expect her research to uncover any resistant populations, he says it would be a "major problem" for growers if it developed.
"As we lose other available herbicides glyphosate becomes more and more important," he says. “Globally there are now 24 weed species with confirmed glyphosate resistance. Most are in North America and associated with GM crops. There are also some cases in Europe, but they are entirely in perennial crops such as vines, citrus and olive crops."
The project tested samples from 40 different blackgrass populations across affected areas of the UK. No resistance was found, and the weed was still being controlled by the field-recommended rate of glyphosate. Laura did however, find variation in sensitivity to glyphosate at lower than recommended doses, with less sensitive populations tending to be from fields with a history of more intense glyphosate use. That really does not bode well in my opinion.
With very little brand new chemistry coming on stream, the farming industry can ill afford to lose these important older products.  I feel that much more should be made of cultural control methods, such as better rotations, crop choice and even, in the case of aphids, beneficial predators. The use of many of these chemicals should kick in as more of a last resort.

I do however realize that this is sometimes easier said than done.  

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