Running down the risks of seedling disease

Sparse emergence might be more than a germination issue, Manitoba Agriculture warns

Soybean seedlings (right) exhibit the suddenly pinched and thin stem that might indicate disease, compared to healthy seedlings on the left.

Poor emergence is a common story for crops caught by lack of rain this year, but seedling disease may be another culprit.

Manitoba Agriculture field crop pathologist Holly Derksen says seedling disease may mimic a poor stand, particularly if infection came in on the seed or if the germinated seed is exposed before it breaks ground.

“(There are) a number of options out there as to what could be causing any sort of seedling disease issue and, unfortunately, there’s a condition for all of those, so we can’t really escape all of them by having certain environmental conditions.”

Seed treatment may also fall short if its window runs out. The province tags a two- to three-week protection period after seeding before effectiveness wears off. Plants past the seedling stage by that point can usually fend for themselves, Derksen said.

This year, however, dry conditions delayed germination in many early-planted fields, and crops may be pushing that seed treatment window.

The province is reminding farmers to compare early-season plant counts with their target seeding rate, both to flag seedling disease or other seed health issues that might have reduced the stand.

The usual suspects

Three pathogens known for root rot are also the ones causing the most broad-spectrum problems.

While some pathogens are crop specific, such as phytophthora in soybeans, a pathogen that Manitoba Agriculture warned was on the rise last year, Derksen also urged farmers to watch out for pythium, rhizoctonia and fusarium, all well known to infect everything from pulses to cereals.

Farmers may hone their scouting eye with a look at the forecast and knowledge of their field. Derksen warned producers with heavy, wet soil to be on guard against pythium, particularly if soil temperature has been cold, soil is compacted or crops are slow to grow, all ideal conditions for the cool-season pathogen.

Moisture is also a friend to rhizoctonia, although the pathogen likes things warmer. Farmers may also want to watch for rhizoctonia if they were forced to delay planting, or in fields high in organic matter.

But while some seedling disease risk may wane without moisture, Derksen warns that dry fields are no promise against disease. Fusarium is a common headache whether it is infecting seedlings, grain or roots, and fields are at risk of the pathogen as long as there is some moisture to kick off infection. Compacted soil will increase that risk, Derksen added.

“Every year, to some extent, we do have infection by fusarium, whether it’s at the seeding stage or later on in development,” she said. “It’s more how stressed that plant is otherwise whether that fusarium will have a big effect on the plant.”

The province has also tagged the commonly named “take-all” fungus, which thrives in cool, wet and alkaline soils, and the warmth- and moisture-loving common root rot pathogen as issues in cereals and grasses. Canola growers should already be looking for the earliest signs of blackleg.

Damped-off plants or pinched stems should also raise the red flag for farmers, Derksen said, although a badly timed scout could hide damping, since the plants will quickly wither.

Some infections later in the season may have actually started while plants were seedlings, Derksen noted, but symptoms did not appear until crops were under more stress.

Is fungicide worth it?

Farmers can do little to stem an infection in the year they notice it, Derksen said, although the knowledge can inform future choices on rotation and seed treatment.

Fungicide in cereals should be targeted to the flag leaf, she said, pointing to data suggesting the flag leaf’s greater contribution to yield.

“Avoid making consecutive application of the same fungicide group on individual fields, and using unlabelled half rates of products could result in quicker development of a fungicide-insensitive pathogen,” Derksen said.

Farmers thinking of delaying herbicide to boost fungicide response should also think twice, she added.

She pointed to an AAFC Alberta study by Kelly Turkington, which found a yield decrease if herbicide was delayed.

Another study out of the North Dakota State University has shown a two- to six-bushel yield jump with early fungicide, she said, although the experiment was limited to high disease pressure where wheat was planted into wheat stubble.

Lionel Kaskiw, Manitoba Agriculture farm production specialist in Souris, urged producers to weigh the economic balance on spraying.

“We really need to sit down and see if it’s a worthwhile investment,” he said. “Sometimes an increase of yield of two to three bushels may not cover the cost of the actual product you’re spraying.”

The province is encouraging farmers to send any suspected seedling diseases in for testing to better tailor management in future years.

About the author


Alexis Stockford

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.



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