Teosinte, a wild grass-like plant, is native to Mexico and Central America. It hardly resembles modern-day corn cobs due to its small ears and tough outer covering. This, though, is the plant ancient farmers selected and reselected over thousands of years via natural mutations to give us the present-day distinctive corn varieties. We now have thousands of corn varieties, from sweet corn types and popcorns, to field corn with grain that comes in very many colours from blue and red to black and purple, down to the commonly grown orange, yellow and white grain types.

Corn as we now grow it in its very many types is entirely dependent on plant breeders, farmers and horticulturalists for its propagation. Corn is now the No. 1 food/feed crop grown in the world, passing potatoes, wheat and even rice. Corn is primarily used as an animal feed grain, hay baled or used for silage production. The high-sugar varieties are used for human consumption, whereas field corn is primarily used as animal feed. Corn is processed into starch, corn syrup, oil and feedstock for alcoholic beverages or biofuels.

In Canada, corn is a warm-season crop, growing its best in the hotter areas of Ontario and parts of Quebec with the higher available heat units. Plant breeders have developed more cold-tolerant varieties of corn in the past few decades, allowing it to grow successfully as grain or silage corn, particularly in the warmer areas of the Prairies. Manitoba, in recent years, has grown around a half a million acres of grain corn (498,900 harvested acres in 2024), followed by relatively little in grain corn production in either Saskatchewan or Alberta. Yields of grain corn in Manitoba average over 100 bushels and upward, resulting in 1.8 million metric tonnes annually. Ontario and Quebec are by far the biggest corn growers, with Ontario’s two million to three million acres resulting in 9.5 million tonnes for 60 per cent of Canada’s corn production. Quebec follows with almost a million acres and 3.4 million tonnes of grain.

Corn yields in the U.S., especially under irrigation and high fertility, can frequently yield 200-300 bushels per acre or more. The current record yield for corn, at Charles City, Virginia, is given exactly as 623.8439 bushels per acre. To achieve such a phenomenal yield, the crop is given all of the macro- and micronutrients needed and regularly irrigated. There is no problem with heat units needed for grain maturation in Virginia — but there is one vital limiting factor needed to achieve this yield.

Did you guess? It’s carbon dioxide. In mid-July an excellent stand of corn supplied with a fully adequate supply of crop nutrients (minerals) at midday may be critically short of carbon dioxide. There are only 422 parts per million (p.p.m.) of CO₂ in the atmosphere, up from 250 p.p.m. in past years. On a hot midday, a C4 corn plant in full sun may be well supplied with water and plentiful nutrients but it cannot get enough CO₂ for its sugar formation. The record-yield growers ensure the corn cropland is loaded with masses of crop residues. These crop residues in the warm moist soil are producing huge amounts of CO₂ as a result of the soil microbes feeding on this residue. This CO₂ moves upward into the crop canopy, where it’s captured by the corn leaves. Unlike those of soybeans or wheat, corn’s leaves have the ability to capture and store this extra CO₂. Under good growing conditions, perhaps with a light breeze for distribution, this extra CO₂ may be rapidly converted via photosynthesis into sugar.

Silage corn acres are on the increase on the Prairies, with around 100,000 silage corn acres in both Manitoba and Saskatchewan and more than 600,000 acres in Alberta making up for that province’s very modest grain corn acreage.

Corn, the world’s largest grain crop worldwide, amounts to about 1.2 billion tonnes. Of this amount some 360 million tonnes are produced in the U.S. for a 31 per cent world share. China is second with 260 million, for over 22 per cent of the total corn crop. Brazil, Argentina and Ukraine are major players accounting for a further 17 per cent. Very many other counties grow the remaining millions of tonnes of corn making up the annual total.

In high-production areas, corn is invariably grown as a hybrid. Seed corn is the offspring of two pure lines of corn referred to as inbred parents. Hybrid seed yields more grain than the parent inbred lines — and much better than open-pollinated varieties. Seed from the female (male sterile) parent is harvested for seed, whereas the male pollen rows are destroyed after pollination or harvested separately.

Enemies

Corn, like other Prairie-grown crops, suffers from many diseases and insect pests. The diseases run from the bacterial, such as Stewart’s wilt, to a variety of fungal diseases. Such diseases include common and head smuts, southern and northern leaf blights, stalk rots, ear rots, rusts, anthracnose and downy mildew. Quite the collection!

The most destructive disease of all in Canada is pink or red ear rot, or Gibberella mould. This fungus, Gibberella zeae, can destroy whole grain cobs and can only be stopped after harvest in the grain if it’s dried down to 15 per cent moisture or less, ASAP.

READ MORE: What to do with mouldy corn

One complaint I have is that my fellow plant disease specialists do an excellent job of confusing corn-growing farmers. Pink mould of corn, Gibberella zeae, is the exact same fungus as Fusarium graminearum. Gibberella zeae is just the sexual stage of Fusarium graminearum. So, put another way, pink mould in corn is the exact same fungus that causes fusarium head blight (FHB) in wheat, barley and other small grains.

Whether on corn or other small grains, like wheat, this fungus produces toxins in the grain, such as DON (deoxynivalenol) and a range of other toxins that are extremely destructive to pigs. Any DON, for example, of greater that 0.5 p.p.m. in feed grain is unacceptable as hog feed. Cattle can tolerate levels of up to eight p.p.m.

When I was a plant disease specialist in Ontario, many years ago, a couple of wet summers in Ontario corn acres resulted in major outbreaks of pink mould in the harvested corn. It became a feed disaster for the Ontario hog industry. So, consider that if you grow corn after wheat or vice versa and have a wet summer or fall, be prepared for possible outbreaks of this disease in either crop in such a rotation.

Final thought: “In the course of my life I have often had to eat my words and I must confess that I have always found it a wholesome diet.” – Winston Churchill

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That’s the message from Dan Undersander, forage agronomist and professor emeritus at the University of Wisconsin. He spoke during a three-day intensive forage workshop hosted by the Canadian Forage and Grassland Association at the University of Manitoba in March.

While many growers are aware of winterkill and stand thinning, they might not realize just how many diseases are chipping away at their yields — or when those issues can start.

“If you don’t know what you’re looking for, you won’t see it,” Undersander says. “And you’ll think that everything is just fine when it isn’t.”

Black stem

Black stem is caused by the fungus phoma medicaginis and is one of the most common alfalfa diseases across Canada’s Prairies. It tends to show up in cool, wet conditions and often appears early in the season.

According to the Manitoba Agriculture website, the disease can be identified in early spring by numerous dark spots on the lower leaves, petioles, and stems. These may expand into large black areas. Infected leaves often turn yellow and fall prematurely, and lesions that girdle the stem can cause wilting above the damage.

“If it causes complete girdling of the stem, then the stems will die,” Undersander says. “If you have enough of that, then your plant will die.”

Early cutting can help reduce losses, as can rotating with non-legumes for a few years before reseeding alfalfa.

Crown rot, root rots

A wide range of fungi — including fusarium, rhizoctonia, and phoma — cause crown and root rot, especially in older stands or those affected by winter injury. Symptoms include stunted growth, yellowing, and poor vigour.

“If crown rot is less than 50 per cent of the crown’s diameter, it’s probably worth keeping the stand,” Undersander says. “But if it exceeds 50 per cent, you should think about turning it over, because there’s a good chance it won’t survive.”

Winter crown rot, also known as snow mould, is another threat to alfalfa and other legumes. It’s caused by several soil-borne fungi that are most active during late fall and early spring when plants are dormant and soil temperatures are near freezing. Once the soil warms above 0 C, these fungi become inactive, and alfalfa is no longer at risk for this disease.

Aphanomyces

Aphanomyces is another type of root rot, caused by the oomycete aphanomyces euteiches, and has become a significant disease in alfalfa production, particularly in wet or poorly drained soils.

“If the seedlings are coming up and the cotyledon dies, but the seedling stays erect — that’s probably aphanomyces,” Undersander says.

It often appears on slopes rather than in low-lying areas, and its biggest effect is on root development. Undersander explained that aphanomyces causes root pruning, which weakens the alfalfa’s root system. As a result, the plants become less competitive, creating opportunities for weeds to invade the field.

Verticillium wilt

This cold-weather vascular disease was introduced from Europe and has been causing problems in British Columbia since the 1970s. It was first detected on the Prairies in 1998, in Manitoba, but has since spread to Saskatchewan and Alberta.

Undersander says it can be identified by what he calls a “thumbprint” on the leaf — irregular, pale or yellowish patches that appear on the leaves, which can resemble the shape or impression of a thumb.

“This is a disease that causes dead leaves on a green stem,” he says. “It causes problems because it’s attacking the vascular system.”

Symptoms are worst in spring and fall. Infected stands may die out in a few years, especially under irrigation. Rotating with cereals or grasses — and avoiding potatoes, sunflowers and sweet clover — is recommended.

Common leaf spot

Caused by the fungus pseudopeziza trifolii, this disease shows up as tiny black or brown circular spots on leaflets, with a lighter brown raised disc in the centre. As the infection spreads, leaves will yellow and drop early, reducing yield potential. It thrives in moist weather and overwinters in crop residue.

Manitoba Agriculture recommends cutting before leaves begin to fall, and using resistant varieties such as Rambler.

Downy mildew

This foliar disease shows up as pale blotches on the top of leaves and a violet, downy growth underneath. Plants may appear bunched or twisted at the top. It’s most active in spring and fall under wet, humid conditions but usually doesn’t cause serious damage.

Undersander points out that downy mildew can be a concern in both spring and fall. “Depending on the time of year, different organisms can be a problem,” he says.

According to Manitoba Agriculture, resistant cultivars such as Algonquin can be used for control, and rotating with cereals or grasses can help reduce infection.

Phytophthora

Phytophthora root rot is especially problematic in poorly drained areas and spreads through standing water in warm weather.

Even if phytophthora doesn’t kill the plant right away, Undersander says, it can severely damage the root. The plant may appear healthy for a while, but when dry conditions hit, it often can’t access enough moisture and will die as a result. He advises digging about six inches to check root health.

“You might keep the alfalfa for the current season,” he says, “but if the root is rotted off, you should plan on turning it over.”

Anthracnose

Though it’s often associated with lentils and dry beans, anthracnose can also be a yield thief in alfalfa — and it frequently goes unnoticed, Undersander says. The disease is identifiable by diamond-shaped lesions on the stem and sudden dieback at the top of the plant.

“There has been good resistance to it,” he says. “And we should think about taking advantage of that, because it will cause as much as a 20 or 30 per cent yield loss if you’re not paying attention.”

Timing matters

The appearance and impact of alfalfa diseases often depend on both the age of the stand and the time of year. Diseases such as phytophthora, pythium and black stem typically show up in new seedings, while bacterial wilt, fusarium wilt, crown rot and verticillium wilt are more common in older stands.

“You wouldn’t expect to see them in the first year or two, but you would maybe see them in the third or fourth year,” Undersander says.

Seasonal conditions also influence disease expression. Some pathogens thrive in cool, wet weather: downy mildew and verticillium wilt, for example, are often seen in spring and fall. Others, such as spring black stem and pythium, emerge early in the season, while summer black stem appears later.

Understanding when a disease is likely to appear can help with diagnosis and inform decisions about cutting, rotation and stand management.

Management tips

Undersander offers several general tips for alfalfa growers aiming to manage disease risk.

He recommends starting with good-quality seed and avoiding planting alfalfa after another legume. Where possible, he says, farmers should stick to planting in well-drained fields to help prevent root rot diseases and avoid wet spots that can foster pathogen growth. Maintaining good pH and nutrient levels is important, he adds, because vigorous plants are more disease-resistant. He suggests controlling insects, since they also introduce pathogens to a crop.

READ MORE: Alfalfa aptitude: five things to consider when selecting varieties

Farmers should also mow new seedlings before old stands, and try to mow clean fields before infected ones, to reduce disease spread.

“Wait till the dew is off before mowing,” Undersander advises. “I don’t recommend expecting all the dew to be gone, but at least a high portion of it.”

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A: The anthracnose pathogen in lentils has been a problem for producers in southern Saskatchewan and other lentil-producing areas. Even with the dry growing conditions in regions of southern Saskatchewan, the disease seems to appear after only minimal rainfall. 

Anthracnose is a fungal disease caused by the pathogen, Colletotrichum lentis. The foliar disease can affect all plant parts, resulting in premature leaf drop, yield loss and plant death. The symptoms usually start at the 10-12 node stage or early flower and first appear on lower leaflets and stems. The disease appears as sunken-in grey- to cream-colored lesions with pin-shaped black microsclerotia present on stem lesions. The lesions progress up the plant canopy infecting large areas of the crop. When infection is severe, stem girdling will restrict nutrient and moisture movement up the stem, causing plant death. Anthracnose is a polycyclic disease, meaning it can have multiple life cycles in one year, which makes it hard to control and allows the disease to spread quickly in the field. 

While anthracnose has been a problem, there are actions you can take to help prevent it. The anthracnose pathogen will overwinter in fields as microsclerotia on infected crop residue. From there it will reinfect the crop mainly through rain splash or wind. Therefore, having a strong crop rotation that gives at least three years in between lentil crops is one of the best methods to combat anthracnose. Rotating out of pulses into non-host crops such as cereals and oilseeds is the preferred option to reduce the inoculum present in the field. 

Additionally, scouting and monitoring fields are important practices producers should implement to prevent the infection and spread of anthracnose. The anthracnose pathogen, like other foliar diseases, favours wet and humid conditions. Producers need to take note of long-range weather forecasts as well as the crop’s microclimate conditions.

If the crop is staying wet in the canopy and there is rain and high humidity in the forecast, the risk of anthracnose is high and a fungicide application may be necessary. 

Producers can turn to fungicides to help prevent and control the spread of anthracnose in their fields. This is a great option, but farmers need to be aware of the resistance risk anthracnose poses to some fungicide groups. Research and surveys done in many lentil-producing areas, especially southern Saskatchewan, have shown anthracnose resistance to Group 11 strobilurin fungicides.

When choosing fungicides, producers must select products with multiple modes of action. Using only Group 11 products may not work to control the disease and can lead to further resistance development. Using combination products that have Group 11 combined with a Group 3 or Group 7 mode of action will provide much better control and mitigate the risk of resistance development.

– Lane Blanke, B.Sc., PAg, CCA, is a manager of agronomic services for Nutrien Ag Solutions in Swift Current, Sask. 

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As of mid-2021, the Pest Management Regulatory Agency (PMRA) expanded the label of a well-established fungicide — Proline Gold — to include anthracnose control in lentils. At the same time, the Proline fungicide label was also expanded to include suppression of the disease.

Last year wasn’t a particularly bad year for the spread of any crop disease, but the expanded label registration will give Prairie farmers another option for controlling the disease, says Rory Cranston, cereal and pulse technical manager at Bayer Crop Science Canada.

As anthracnose favours warm and wet growing conditions, 2021 wasn’t a runaway year for any type of disease pressure, but Cranston says that doesn’t mean the disease disappears completely. “There is a good chance that fields might have passed the drive-by test (last) year,” he says. “They weren’t seriously affected by the disease, but often with a closer look at plants there was still some infection there.” Cranston says under more ideal conditions, anthracnose can be a very “robust” disease with multiple life cycles infecting crops.

“With the label now including Proline Gold for use in controlling anthracnose in lentils, Prairie producers have an effective fungicide with a different mode of action,” says Cranston, describing it as one more tool in the crop protection toolbox.

Pathogen insensitivity

In recent years, lentil growers and researchers have found that after repeat use of fungicide products based on Group 11 (strobilurin) chemistry, the disease is showing increased “insensitivity” to those products.

Proline Gold has two active ingredients effective against anthracnose, and neither is a Group 11.

“Proline Gold provides effective control with Group 7 (fluopyram) and Group 3 (prothioconazole) chemistries,” says Cranston. It is a good product to use as a follow-up to a Group 11 to control any disease pathogen that may be showing resistance.

He recommends herbicide layering with application of two different products to provide the most effective control against several pulse crop diseases.

For example, he recommends an early application of Delaro 325 SC (Groups 3 and 11 chemistries), which is effective against ascochyta blight, grey mould, white mould (sclerotinia) as well as anthracnose. That treatment can then be followed with a second application of Proline Gold (Groups 3 and 7). It provides sort of that one-two punch against anthracnose including pathogens that may have Group 11 insensitivity.

Along with anthracnose, Bayer also received the registration of Proline for suppression of Botrytis in both lentils and chickpeas. This expansion is complementary to Bayer’s complete pulse fungicide lineup, including Delaro and Proline, offering growers solutions across crops, disease pressure and resistance concerns.

Widespread disease most years

Sarah Anderson, Saskatchewan Pulse Growers (SPG) agronomy manager, says recent disease surveys have shown that anthracnose is the most prevalent disease in lentils across Saskatchewan. Surveys in 2018 and 2019 showed the disease was found in 74 and 92 of surveyed lentil fields, respectively. In 2020, field survey crews inspected more than 1,000 fields, including 68 lentil fields and 41 pea fields in Saskatchewan. Anthracnose was found in 84 per cent of lentil fields inspected.

In 2019, high levels of insensitivity of the anthracnose pathogen to Group 11 fungicides was confirmed in Saskatchewan lentil fields. Testing to confirm this insensitivity revealed a mutation (G143A) that enables the pathogen to have cross-resistance to all Group 11 fungicides. This means that no fungicide active ingredient within Group 11 will provide effective disease control in fields with high levels of insensitivity. (Although the words “insensitivity” and “resistance” are sometimes used interchangeably, plant pathologists prefer to use the term insensitivity to refer to the resistance of the pathogen to a fungicide since the term resistance is typically used to describe the resistance of a host plant to a particular pathogen.)

Anderson says with light to medium disease infection levels, usually showing up at early flowering, the first sign of the disease is usually white spots appearing on lower leaves and stems. The leaflets will wither and fall to the ground, which is premature leaf drop.

“If you start to see lesions on stems and leaves, then the disease has progressed considerably,” she says. And, as with many or most diseases, by the time you see disease symptoms in the crop, it is too late to apply any effective treatment. With anthracnose, the lesions grow and girdle the stem, affecting nutrient supply to the plant. Eventually the disease chokes the plant completely and it dies and falls over.

Anderson says anthracnose is a pathogen that lives on crop residue and can flare up if crop and environmental conditions are favourable. Anthracnose favours frequent rain, high humidity, dense canopy, warm temperatures of 20 to 24 C and a lot of leaf wetness. And, again, depending on conditions, the degree of infection can range from light to severe. With some of the more severe field infections, yield losses can be as high as 50 per cent.

While it is great to have fungicides available, SPG urges farmers to use an integrated approach to prevent or reduce the severity of anthracnose.

The SPG strategies for integrated anthracnose disease management can be found in this document at saskpulse.com.

Additional information on anthracnose in lentils can be found at the SPG website.

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