The reality of chemical controls is always going to be that relatively speaking they’re a blunt tool. But that also means they’re going to be under scrutiny to ensure their safety.
And the safety track record of these products is getting better and better by the season, according to John Gavloski, provincial entomologist.
“In an ideal world, we would have insecticides that would kill the pest that we want to kill and not be harmful to us or wildlife and not end up in our water systems,” Gavloski said during his Manitoba Agronomists’ Conference presentation earlier this winter. “We aren’t there by any means, but things have improved greatly over 50 years.”
As a case study, Gavloski discussed flea beetle management in canola. Fifty years ago, there were few seed treatments apart from lindane and no granular insecticides available. The only foliar treatments available were DDT and Malathion. By the mid-’80s DDT was taken off the market.
“DDT was a popular product but there was a lot we didn’t know about it when it came out,” said Gavloski. “We found out more through trial and error that it is very persistent, it bioaccumulates, so if the aquatic organisms eat it, fish eat aquatic organisms, bird eats fish, it just keeps building up into higher levels through the food chain so there was a lot of ecological harm. A product like that would never get registered nowadays.”
In 1980, Furadan (carbofuran), a carbonate pesticide, came onto the market as both a granular product that could be applied with the seed and as an organophosphate foliar spray. To assess toxicity of products, a figure called the LD50 is used. The LD50 is the dose that will kill 50 per cent of a test population, generally lab rats. A dose that will kill 50 per cent of rats is the lethal dose. So, the lower the LD50, the more toxic the product is. Malathion has a LD50 between 4,000 and 5,000. Furadan’s LD50 is very low at five to eight.
“So, a very toxic product but that was one of the go-to products at seeding in the ’80s,” said Gavloski.
A few more products came to market in the 1990s, such as Counter. Its LD50 was between eight and 13, so still in the toxic range.
“With either Counter or Furadan granules, if a bird or mammal the size of a mouse was to eat one or two of these kernels that’s enough to kill them, so that was one of the big problems with these products,” said Gavloski. “Even a little bit of dust on your finger if you end up ingesting it would be enough to kill a person and incidents did happen like that. So, these were products you had to be careful with.”
Another thing that was happening in the 1990s was that pyrethroids started to come out under trade names Cymbush, Decis and Ripcord, which were less toxic to humans and without some of the environmental concerns of carbonates and organophosphates.
By 2000, some products like Furadan and Counter had disappeared or were on their way out. Lindane had been voluntarily withdrawn due to market concerns in 1999 but growers could use up existing product until 2001.
At the time, Gavloski remembers a lot of discussion about losing Lindane and what canola growers could do to control flea beetles.
“Farmers were saying we’ll have to spray multiple times for flea beetles, it’s the only way we’ll be able to grow canola,” said Gavoski. “We all know that didn’t happen, so things changed when this happened and we still grow canola and we grow it quite well.”
By the early 2000s, neonicotinoids under trade names such as Gaucho, Helix and Prosper were being introduced. The neonics took over as the go-to solution for seed treatments in canola and that’s still the case today.
The top three seed treatments for flea beetles in canola listed in the 2018 Manitoba Guide to Crop Protection are neonics, followed by Sulfoximines and Diamides, which are different groups. Just as they were when Lindane was discontinued, growers fear that without neonics they will have no option but to make multiple foliar applications, but Gavloski isn’t convinced that will be necessary.
“Sulfoximines and Diamides are costlier but we will still have seed treatment options,” says Gavolski, who also predicts new products will continue to come to market during any phase-out period for neonics.
He’s also keeping an eye on a couple of new innovations currently being worked on that could be coming down the pipe for growers, including a hairy type of flea beetle-resistant canola and RNAi interference technology that is specifically targeted to silence certain genes within flea beetles and does not harm any other insect species.
Flea beetle-resistant canola has been in the works for several decades and a lot of pro-gress is being made. Scientists looking at wild grasses and strains of canola for some flea beetle resistance, discovered that one stood out: Arabidopsi thaliana L. It has hairy leaves that flea beetles do not like.
Researchers at AAFC in Saskatoon were able to breed that trait into canola but the resulting plants only had hairy leaves, not stems, so there could still be some stem feeding by flea beetles.
“Since that study was published in 2011, there’s been a new line produced called Hairy 2, and these canola lines have hairs on the leaves and the stems so that would help protect the whole seedling and not just true leaves, which is very encouraging research,” says Gavloski.
The next step is to get the trait into commercial varieties, which is tricky but there are breeders currently working on doing that.
“We’re probably looking at mid-2020s at the best, but it’s happening,” says Gavloski.