Don’t lose sight of what’s beneath the soil

Out of sight is not out of mind when it comes to soilborne diseases. It’s easy to forget about what you can’t see, especially after a drier than normal season and when early seed tests are looking good. But soil-borne disease pathogens are well established across the Prairies and in particular in Manitoba. Without a proactive approach, what lurks beneath the ground can cause big problems in your cereal crop in the coming season.

“Growers aren’t sure what to expect for the 2018 growing season,” says Brittnye Kroeker, a SeedGrowth Specialist with Bayer Canada. “In 2017 the seed-borne disease levels were extremely high. A wet growing season in 2016 brought high levels of disease and an increase in the presence of pathogens on the seed. Early indications for this year show that the seed is looking much cleaner. But seed only tells one part of the story. Soil-borne diseases are hardy and inoculum levels remain very high.”

In 2017, more cereal seed was treated than in the past in part due to the high levels of disease in the seed and soil coming out of the disease-intensive 2016 growing season. Increases in the levels of fusarium in cereal seed was the main reason growers turned to seed treatments. Growers who saw disease damage in their crop in the past are generally more likely to continue to treat for those diseases, even after a dry summer.

“Soil-borne diseases cause root rot and seedling blight in cereal crops,” says Holly Derksen, a field crop pathologist with Manitoba Agriculture. “When it’s dry you often won’t see as many symptoms of the disease until the crop gets a bit bigger, but dry root rot can be very damaging to your crop. In a dry year, strong roots and complete root systems are often even more important because as the crop gets bigger it will need all the roots it can get.”

While different diseases cause varying symptoms, signs of damage include brown lesions on the cotyledon ,stunted growth, or can cause plants to dampen off (die). , Growers may notice a reduced/uneven plant stand as a result of some of these diseases. An uneven stand may lead to some Plants with more tillers, which means they may flower later and less evenly, making timing for a fungicide application more difficult and making maturity vary for preharvest applications.

“Some of the damage you see early in the season includes seedling blight,” says Derksen. “The plant may have low levels of emergence or may not emerge at all, and growers may just attribute that to seed or seeding issues rather than disease. When soil-borne disease strikes cereal, what seedlings do emerge could die off, or have damping off. Unless you are out there scouting daily it can be hard to see the earliest signs of soil-borne disease.”

Visual damage is information to file away for the following growing season, as at that point the damage has already been done to that season’s crop. The spores that cause soil-borne disease move easily throughout the soil or air and even if the soil tests good one year, there can be high levels of inoculum during the following growing season.

Insurance for your seed

Once the crop is past the seedling stage, it is less likely to be impacted by these same soilborne disease, but by then the damage is done. A poorly established crop with stunted growth and uneven staging is less likely to compete against weeds, and is more susceptible to in season stressors making it a target for other diseases and potential insect damage.

“Treating your seed will protect it against more than seed-borne disease, it will also help protect your crop from early  season damage caused by soilborne diseases ,” says Kroeker.

“Germination is a critical time for the plant, so choosing a good seed treatment will help set the crop up for success. Make sure you are using the right seed treatment for your disease profile, and that you have adequate coverage to start your season off with 100 per cent chance for success.

Everything you take away from those early seeding decisions will ultimately have an impact on your yield.”

Kroeker also says that adding an insecticide to your seed treatment is the only way you can protect your crop from wireworm damage if that is a concern. “Wireworms can survive at the larvae stage for 3-5 years and we currently do not have a product that kills them,” she says but using an insecticide seed treatment will keep them from damaging the cereal crop in its more vulnerable stages.”

Derksen says that while growers are more likely to routinely apply a seed treatment to some crops such as canola and pulses, cereal growers are increasingly treating their crop as their seeding dates move earlier each season.

“Growers are getting their cereals in the ground as early as they can in order to manage their seeding timeline, and to get the most possible yield potential,” says Derksen. “In cold soils the seed will sit longer and be more susceptible to disease damage. Seed treatments are most effective for a maximum of three weeks after seeding, so plants need to get past the vulnerable seedling stage before the seed treatment wears off.”

Managing one year to the next

While crop rotation is important for many aspects of farming, it cannot be used as a standalone method to control soilborne diseases. Most current disease threats are not host specific, meaning they can live on different crops or residues, or can live in the soil or on the roots of other crops for several years. While the tendency is to look at what happened last year, in reality the disease pathogen will have built up over several seasons.

Root rot in barley. Despite a dry year in 2017, inoculum levels in soil are still very high. Photo: Kelly Turkingt on,AAFC

Derksen says good agronomics can also help a seed fight against soil-borne disease. “Growers always want to seed into the best conditions they can, but this is especially important when it comes to disease management,” she says. “Seed into well-drained soils, and be very mindful of seeding depth. The longer it takes to emerge the more it can potentially come into contact with disease and other threats.”

While disease is very weather dependent, it is a persistent myth that growers will avoid soil-borne disease if the soil in warm and dry. Fusarium graminearum and C. sativus both do well in warm and dry soils, and they only need a small amount of moisture to become problematic. Pythium will thrive in wet and cool conditions. At this point growers need to make their treatment decisions based on the idea that the disease is there, and how they want to address it in any given year.

“You can’t predict the weather — over the past two years we’ve had extremes of wet and dry,” says Kroeker. “But you can manage for it. Choose varieties that have the most built in resistance where possible, and treat your seed to help manage the risks that are out of your control. Seed treatments help your seed put all its resources into growing rather than battling threats, to help get it successfully past the seedling stage.”