Disease considerations for a late and wet spring

In the west, it could mean more clubroot transmission. In the east, growers should be concerned about phytophthora in soybeans

Wet conditions will increase the chance of clubroot-infected soil sticking to machinery and being transferred to other fields.

At the time of writing, spring moisture conditions in Eastern Canada remained to be seen, but there wasn’t much question about the Prairies — many growers would still be dealing with wet soils and late planting due to rain and snow from last fall. For example, by early October the Western Cypress Hills area of Saskatchewan had received 40 cm of snow and several areas of Manitoba received more than 60 cm. Alberta Agriculture & Forestry reported that by early December, snowpack had nearly reached one-in-50-year highs throughout the southern Peace River Region.

While wet or waterlogged soil generally means more disease pressure, Bruce Murray is quick to point out that this is not always the case. “Many of the seedling diseases will show up under saturated soil conditions but to really take off, additional factors are required,” says Murray, the market development agronomist (eastern Manitoba) at Bayer.

He points to many stressors that put a strain on soybean plants, greatly boosting the chances of successful fungal infection. Compacted soil is one. Injury from herbicide residue from the previous year is another. Deep seeding and iron deficiency chlorosis (IDC) injury due to high-soluble salt and/or carbonate levels in the soil also cause plant stress. Plants can also be stressed from trying to grow in cold soils over extended periods. “So again, while it’s true that with wet soils we may see more disease pressure showing up in the spring, wet soils alone do not guarantee the occurrence of fungal disease,” Murray says. “The presence or non-presence of multiple stress factors matters a great deal.” Seed treatments provide additional protection if one or more of these factors cannot be avoided.

Bayer SeedGrowth specialist Brittnye Kroeker points out that some farmers incorrectly believe that if soils warm up and dry out by planting time, seed treatment is not needed. “Yes, seedling diseases like pythium, rhizoctonia, and phytophthora only really thrive under wet conditions, but other fungal pathogens like fusarium can be active in wet but also in dry and warm conditions,” she says. “Therefore, farmers should always consider seed treatment a must, no matter what conditions prevail at planting in any particular year.”

Phytophthora threat in Quebec

In Quebec, the corn harvest of 2019 was very late, finishing in January, and Bayer market development agronomist Stephane Myre notes that some of that remaining residue will shelter phytophthora, which will in turn threaten soybeans planted in the same fields this spring. If soils are cool and wet, the threat looms larger and growers should therefore choose soybean cultivars resistant to several breeds of the fungus.

Remaining residue from last year’s corn crop will shelter phytophthora, which will in turn threaten soybeans planted in the same fields this spring. photo: D. Malvick, University of Minnesota

“Phytophthora is the most serious disease threat to soybeans in Quebec right now, and seed treatment is really important,” Myre adds. “In corn, pythium wasn’t a big problem during the last couple of years, due to planting happening later in drier and warmer conditions, but this year, who knows how wet things will be? There was also some presence of gibberella ear rot in Ontario in 2019 and also some anthracnose here and in Ontario.”

Containing clubroot

Elizabeth Simpson, canola agronomic systems manager for Bayer, says wet soils are a particular hazard for spreading clubroot in canola, but that regardless of what crop is being grown in a field, the risk of spreading this disease will always be present. Wet conditions allow clubroot to move within a field through water flow as well as in wet soil stuck on equipment. If you have identified an infected field on your farm, Simpson advises seeding clubroot patches and entryways with a perennial grass to limit pathogen and soil movement. Also, ensure your equipment is cleaned and disinfected before leaving an infected field, and if possible, work in your potentially infected fields last.

Adam Pfeffer, national row crop agronomic systems manager for Bayer, also reminds growers of the importance of rotation. Indeed, he “definitely encourages” growers to plant an entirely different crop category in your crop rotation, for example moving legumes to acreage that grew cereals. “Obviously, also avoid sequential crops with similar disease susceptibilities,” he adds. “For example, soybeans, sunflowers and canola are all at risk of white mould pressure.”

Tracking moisture by field

To most efficiently track soil moisture levels this spring, Bayer field product specialist Andria Karstens points to the Climate FieldView app which provides growers with daily rainfall data for each field. “While a rain gauge records the precipitation for the few square inches it covers, the intensity of rain can vary greatly from one side of the field to another,” she explains. “So you will often get different readings depending on where you put your gauge.” Instead, Climate FieldView provides a “whole field” rainfall measurement. Looking at whole-field precipitation, says Karstens, will help you understand the varying workability of your fields, in addition to showing you how your fields are trending over the season — too wet, too dry or just right.

Growers should also understand the way the platform works, integrating live weather data feeds from various sources including weather stations, rain gauge networks and radar. This means that its readings are updated as needed each hour as more quality-controlled data is received. “So the measurements sometimes change over time, but you can be assured that if they do, their accuracy has increased due to integration of the latest possible data,” Karstens explains. “Simply click on the ‘Weather’ icon to see the amount of precipitation in each field, since yesterday, since midnight, season-to-date and also the amount compared to the 10-year average.”

Kroeker notes that an increasing number of growers are doing small field trials to better manage their crops for fungal disease control and more, and that the FieldView app is very helpful in obtaining meaningful conclusions from these trials. “If you are going to invest in doing your own trials, you want to make sure you are getting the most useful data out of them that you can, this year and in years to come,” she explains. “Data is not useful unless it’s managed in a way that results in much better decisions.”

This article was originally published in the 2020 Disease & Yield Management Guide, a Country Guide Special supplement sponsored by Bayer Crop Science.

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