Pest and Disease Outlook 2020

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A barley leaf with scald symptoms. Photo: Kelly Turkington

Top pest and disease concerns in Alberta for the coming year. 

After a couple of dry years, 2019 was a wetter year in most areas of Alberta, at least in the second half of the growing season, which allowed some crop diseases to rear their ugly heads. This may very well affect what diseases are most threatening in 2020, but the weather will, as always, be a huge factor.

With cereals and canola, Agriculture and Agri-Food Canada (AAFC) plant pathology research scientist Kelly Turkington explains even though it was dry in 2017 and 2018, there may still have been background low-level infections in lower crop canopies and, thus, potential inoculum, especially for cereal leaf diseases.

“When the moisture arrives, even a low level of cereal leaf spot inoculum on old crop residues can be a concern,” says Turkington, who is based at the AAFC Lacombe Research and Development Centre. “A lot of the leaf spot diseases in barley and wheat are polycyclic, which means they have many cycles of spore production, dispersal, and host infection, with some cycles being as short as seven days. With moisture present, they can quickly produce large amounts of spores and build up to damaging levels.”

Seed testing lab results dating back from before 2012 illustrate the continued expansion of Fusarium graminearum in cereal seed samples in Alberta, notes Turkington. Levels of detection decreased in 2017 and 2018, but moist conditions in central and northern Alberta (as well as irrigation in southern Alberta) resulted in F. graminearum detections skyrocketing in 2019, but not at 2016 levels.

In cereals, as in years past, Turkington says root rots should not be too much of a problem unless growers are planting barley-on-barley or wheat-on-wheat (although no-till seeding helps reduce the impact of diseases such as common root rot). Disease survey results suggest the development of the Septoria leaf disease complex in wheat and this will also be an issue to watch for in 2020.

Fusarium head blight symptoms in wheat. Note the prematurely ripened affected portions of the head, and the brownish discolouration of the rachis and upper stem tissues. Photo: Kelly Turkington

In barley, scald is also a threat, but mainly in cooler western Prairie regions. “If you had a significant amount of scald in 2019 and you need to grow barley in the same fields this coming year, you should change varieties and pick a variety with as complete a resistance package as possible, not just for scald,” advises Turkington. “For silage or forage production, keep in mind that we did a trial where we planted a mixture of triticale, oat and barley, which reduced leaf disease development resulting in better yield than growing the same barley variety continuously.”

In addition, take-all root rot disease is always a risk in wheat-on-wheat, notes Turkington, but it can also infect barley, although levels in both crops appear to be reduced compared to years ago. Growers should also keep in mind that take-all does better in alkaline soil, so Turkington says, “if you’ve applied lime to deal with clubroot in canola, watch out.” In canola, he points to sclerotinia stem rot, clubroot and blackleg as risks for 2020, although the extent will depend largely on the weather.

To mitigate all disease risk in 2020, Turkington advises a close look at field history to help producers choose the best variety possible or to signal the need to extend crop rotations. For example, if they had issues with leaf spot disease and/or fusarium in the cereals planted in previous years, producers should choose a variety with at least a moderate level of resistance. Turkington says there is excellent stripe rust resistance in today’s wheat varieties, from moderate to full resistance now available.

The disease ratings of previous variety choices will also give insight into which growers should choose for 2020 or if a more extended rotation is needed. Turkington adds that fungicides are key tools for in-season disease management, and crop scouting will always be critical to determine if the disease risk warrants a fungicide application.

Lastly, besides good crop management practices in 2020, Turkington advises growers to send samples of their 2019 harvested grain to a lab for a “full fungal scan” test, which will indicate what fungal diseases were present on the crop and to what extent. This information can be used to further tweak a disease management program, with regard to seed and seed treatment choice, as well as length of rotation.

Pulse Outlook

As with canola and wheat, pulses experienced an upsurge in fungal disease levels in 2019 due to all the moisture. Robyne Bowness Davidson, pulse research scientist at Alberta Agriculture and Forestry, says Mycosphaerella (Ascochyta) blight was present at high levels in the 2019 field pea crop and if the 2020 growing season is wet again, it will also be a large concern due to higher inoculum levels that will overwinter in the crop debris. “It was present in every single field surveyed regardless of whether or not producers applied a fungicide,” she explains. “Downy mildew, another foliar disease of pea only seen in wet years like 2019, may also be a concern in 2020 due to higher inoculum levels.”

Sclerotinia, a foliar pathogen, and Aphanomyces, a root rot pathogen, were also present in field peas in 2019. Both diseases thrive in high moisture, overwinter in the soil and affected lentils in 2019 as well. Sclerotinia is a potential threat in many broadleaf crops, and can move from canola to pulses or vice versa. Ascochyta was also observed in lentils in 2019, but Davidson says the fact that there is not a large acreage of lentils in Alberta at present helps prevent it from becoming a serious concern.

Blackleg lesion at the base of a canola stem showing small black pycnidia (asexual fruiting bodies) of the blackleg fungus. Photo: Kelly Turkington

“In faba beans, the main disease concern is Chocolate spot (caused by Botrytis), present in 2019 due to the wet weather,” she adds. “It tends to move in later in the season and can affect yield. We will continue our work in this area to determine the application timing, rate and efficacy of various fungicides. Our research on this has actually been going on for four years, but 2019 was the first year this disease was present at high enough levels that we could study it due to the moisture.” In general, faba beans are less affected by root diseases due to a larger root structure, she adds. They are resistant to Aphanomyces and seed treatments work very well to control the other root rot fungal threats.

Insect Threats

The No. 1 threat for canola producers in 2020 is likely flea beetle, says Scott Meers, insect specialist with Alberta Agriculture and Forestry. These will be striped flea beetles, except in the extreme south of the province where it’s the non-striped variety. “If the canola crop is able to grow fast in the spring, they won’t be as bad,” explains Meers. “There are no new control products available, so I’ve been stressing good plant stand establishment. Flea beetle populations are exacerbated by low plant populations, but there’s a lot of pressure on growers to seed more lightly because seed is so expensive. You can do that, but as I have been saying to growers all this year, you are risking higher beetle numbers and you’ll have to do things to control them.”

Canola growers may also face bertha army worm, where there was an outbreak in the Peace region, and some cases in central and southern Alberta in 2019. Cabbage seed pod weevil is a steady threat in all growing regions, but a little more in the east.

In wheat, Meers reports wheat midge is on the increase in central Alberta due to the wetter weather in the past year, with pockets in various areas. The drier weather in southern Alberta has allowed the wheat stem sawfly to build into a serious problem. Growers in central and southern parts of the province also face serious grasshopper potential. “In barley, there are no real concerns,” he adds. “In peas and fava beans, there’s pea leaf weevil, and every year there is some pea aphid, especially in lentils in southern Alberta depending on the year.”

For more information visit the Prairie Pest Monitoring Network Blogat http://prairiepestmonitoring.blogspot.com/?m=0and the Fusarium Head Blight Infection Risk Reportat https://agriculture.alberta.ca/acis/fusarium-risk-tool.jsp.