Pulse and soybean disease roundup

Managing disease in these crops may be a particular challenge this year

Producers should also be on the lookout for phytophthora 
root rot in soybeans.

Though crop diseases are a concern every year, they may prove particularly challenging in 2020 after last year’s difficult, wet harvest. Since the most successful farmers are proactive and prepared, it may pay to be ready to tackle whatever disease challenges Mother Nature throws your way this year.

“I would say my biggest concern for disease is that a lot of post-harvest weed control did not take place on many acres,” says Nevin Rosaasen, Alberta Pulse Growers’ policy and programs specialist. “Not having good weed control going into your rotation is a bridge for diseases between crops. For growers using reduced tillage or zero till, it’s important to know that even if you hit it with a glyphosate plus tank-mix partner, that residue will still be there.”

Be aware too that seeding into a standing crop that wasn’t harvested last year could add a lot of disease pressure due to moisture in the still-standing canopy.

Root diseases

Root diseases should also be top of mind, especially for Manitoba producers, as we move into the 2020 season.

“We’re expecting more saturated soils due to the rains late last season. Manitoba is usually a wetter province and last fall was a record year for fall precipitation,” says Cassandra Tkachuk, a production specialist with Manitoba Pulse and Soybeans.

Root diseases typically attack between germination and early flowering, often presenting as poor emergence and stunted, yellowed seedlings. While Saskatchewan and Alberta farmers shouldn’t entirely relax their guard, their typically drier springs means their soils are less likely to foster root rots on a more widespread basis. (Local areas may still be at high risk if conditions are favourable or problems have occurred in the past.) Manitoba producers aren’t so lucky: particularly this year, they may face a higher risk of pythium, rhizoctonia, botrytis, fusarium and aphanomyces across all pulses.

Producers should also be watching for phytophthora in soybeans. That said, on a positive note, last year Manitoba researchers found phytophthora in just four of 83 surveyed soybean fields, less than five per cent of submitted fields.

In Alberta, the root disease of concern is aphanomyces. And, adds Rosaasen, fusarium is now “almost ubiquitous across the Prairies.”

Producers should also be on the lookout for pea leaf weevils, which can travel long distances and carry root rot pathogens.

Root diseases are not the only diseases that could come on with a vengeance due to last year’s harvest conditions, however.

Ascochyta, anthracnose and others

Due to the high acreage of lentils in Saskatchewan and field peas in both Alberta and Saskatchewan, producers in those provinces are particularly at risk of ascochyta, anthracnose (lentils), botrytis (lentils) and sclerotinia, if conditions are favourable for foliar diseases.

The ascochyta disease complex most commonly presents as mycosphaerella blight in peas. The blight can be seen first on lower leaves, stems and pods as small, purplish-brown spots that grow together and spread up the plant. It can also girdle plants, causing lodging. While choosing a variety with more tolerance is a good management tool, control hinges on fungicide timing.

The blight also attacks chickpeas.

“With chickpeas, we’re starting to figure out how to manage ascochyta and as well we have some resistance in the varieties,” says Sherrilyn Phelps, agronomy manager with the Saskatchewan Pulse Growers. “But ascochyta in chickpeas is very, very aggressive. If it’s not managed quickly and extensively, it’ll wipe out entire crops.”

Faba beans are gaining popularity in Saskatchewan and Alberta in recent yeas. Faba’s main disease of note is chocolate spot (botrytis). That said, Saskatchewan researchers identified both stemphylium and alternaria in surveys last summer.

“We don’t know yield losses yet (from those diseases) because they’re so new. That was the very first time we’d seen a high level of those diseases in faba beans. There’s so much more work that needs to be done to identify whether those are diseases of note or whether they are secondary infections,” says Phelps.

Soybean cyst nematode

Soybean cyst nematode (SCN) is a growing concern in Manitoba and eastern Saskatchewan fields. It was found in four Manitoba fields in 2019. Though technically a nematode, this pest is classified as a disease in both Ontario and the United States.

“We have been monitoring for SCN since 2012. It’s the No. 1 pest concern of soybeans in the United States and it has been moving northward,” says Tkachuk. “The levels are still very low here. Though it was just identified in random samples and there are no above-ground symptoms yet, I do suspect it’s more widespread than we think.”

Now, while infection rates are still low, is the “perfect time” to enact safety measures to counter SCN, says Tkachuk, especially since the SCN identified could potentially already be a resistant strain inherited from other regions. Specifically, prevent soil movement between fields and rotate in non-host crops, ideally according to a four-year (or more) rotation.

“We need to learn from our neighbours to the south and start proactively managing it,” Tkachuk says. “By the time you see above-ground symptoms, you could be getting up to 30 per cent yield loss. And it’s a tricky thing because when it does have above-ground symptoms, it looks like a lot of other diseases (or conditions such as the impact of salinity). But, even if you don’t see it, it doesn’t mean you don’t have it.”

Watch for SCN infection in weaker areas of the field such as drains, approaches and saline patches. In particular, watch for sudden death syndrome, which tends to move with and can be more obvious than SCN. Dig up root samples and look for cysts. If cysts are present, consider sending samples to Mario Tenuta, a professor of applied soil ecology for the department of soil science at the University of Manitoba, who is currently surveying for SCN via molecular study.

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