Some farmers consider seed treatments an insurance policy to try and ensure their crop has every opportunity to germinate and establish healthy plants. Others see them as another added cost they don’t need, especially if they haven’t had any serious disease issues for a while.
Invariably though, once a farmer has had a disease problem costing a significant amount of yield, seed treatments become standard practice. As is often the case, it’s “once bitten, twice shy” when it comes to seed treatments.
“A lot of people who don’t use seed treatments get away with it for a lot of years, and then suddenly have a problem where they have too much smut or they’ll get common root rot or take all root rot. They then realize they should maybe have applied a seed treatment,” says Harry Brook, a crop specialist with Alberta Agriculture and Forestry. “Seed treatments are a significant cost, so probably the best way to think them is as insurance, and it’s up to individual farmers to assess their risk based on their crop rotation, the conditions at seeding and how comfortable they are with the amount of risk that’s involved.”
Seed treatments may benefit short rotations
Common root rot can be especially problematic because it affects most cereal crops. If farmers are growing another cereal crop this year, and had common root rot in the same field last year, they should certainly pencil in a seed treatment. Shorter crop rotations — such as wheat/canola — in general are at higher risk for disease problems.
“A longer, varied crop rotation means there is less chance of disease organisms building up,” says Brook. “With a short, minimally varied crop rotation we’re setting ourselves up for disease issues because the more we grow the same crop, the more opportunities there are for pathogens that attack that crop to multiply and flourish. That increases the risk of disease and crop failure, so it might be more advantageous to use seed treatments.”
But for farmers who have a long rotation, and a smaller number of acres to seed — so they can allow time for the soil to warm up and become moist — a seed treatment may not pay every year.
Coping with smut and bunt used to be part of growing cereals on the Prairies, but fungicide seed treatments are now very effective in killing these pathogens. Invariably, says Brook, whenever he talks to farmers who have seen a lot of smut or bunt in their crops they haven’t bothered with a seed treatment. “The problem is if you are planting untreated seed with smut spores on the seed, you are going to get smut,” says Brook. “If you’ve never had smut and you’ve got very warm soils — around 7 C to 8 C and there’s good moisture so you can seed shallow, then the big advantage of disease prevention through a seed treatment is removed.”
Seed treatments and fusarium
Seed treatments’ effectiveness against fusarium depends on the species and levels of fusarium in the field.
Infections due to fusarium, including F. graminearum, are another big issue that cereal farmers seem to be dealing with on a regular basis. The first defence against this disease should always be using clean seed, says Pratisara Bajracharya, a pathologist with Manitoba Agriculture, Food and Rural Development.
It’s also important to know what species of fusarium is causing the infection, she says. Fusarium graminearum is an aggressive species of fusarium which causes problems in the field, including emergence problems and fusarium head blight,” says Bajracharya. “It’s always a good idea to get your seed tested, and if around two to three percent of the infection is due to F. graminearum, it might be worthwhile to invest in seed treatment. If there is five per cent of F. graminearum present, the seed treatment may not work very efficiently. In that case, a farmer would be better off not using that seed at all. If you do a seed test and find that the predominant species of fusarium in that sample is species other than F. graminearum then the tolerance level is about 10 per cent, at which stage it is effective to use a seed treatment.”
Using a seed treatment will not prevent fusarium head blight during the later growth stages — such as during anthesis — but will help in management of early season issues like poor emergence and seedling blight caused by Fusarium spp, adds Bajracharya.
Canola seed comes treated
Farmers, of course, don’t have to make that decision when they plant canola, which comes with a seed treatment that includes both a fungicide and insecticide.
Some researchers are looking at shifting populations of flea beetle species in canola crops. “Neonicotinoids insecticides in canola seed treatments are specifically designed to deal with crucifer and striped flea beetle. Canola is most susceptible to feeding by these pests just after emergence. But the population of flea beetles on the Prairies is shifting to the striped species. The interesting thing is that the crucifer flea beetles were well controlled by the neonicotinoids, and now they’re finding that it’s not as effective at killing off the striped flea beetle, which is gaining predominance,” says Brook.
“Are the neonicotinoids on our seed treatments in canola causing the shift away from the crucifer flea beetle to the striped flea beetle, or is it just naturally occurring because of weather patterns and conditions? There is some research being done but I don’t know that they have come to any conclusions other than they can see there is a shift in population.”
As farms get larger and have many more acres to seed in a short window, more and more farmers are using a seed treatment as a matter of course, often to protect crops that they need to seed early into less than favourable conditions. Brook believes larger farms have less time to treat individual fields differently. “If they’ve got 10,000 acres of wheat to go in they will seed treat everything because they don’t have time to pick and choose,” he says.
One seed treatment company is suggesting that the product in their seed treatment can improve yield through making the plant more nitrogen-use-efficient, and although Brook says that might be the case, the impact is not always significant. “Ultimately, when it comes down to yield in our country, our prime limiting factor tends to be moisture,” he says.
With such variability in weather conditions from year to year, it’s hard to assess how much risk you’re taking until something actually happens, says Brook. “Often once farmers have been hit with a disease they will use a seed treatment on a regular basis because they just don’t want it to happen again,” he says. “To seed treat or not to seed treat is a complicated decision based on current physical conditions, past history and perceived risk. It is a very individual decision.”