Moisture is the enemy when it comes to forage diseases.
For any farmer who has watched dark splotches appear on their low-laying alfalfa leaves or opened a bale only to find it spoiled, that will come as no surprise.
Fungi are the culprits for most forage diseases, Linda Jewell, AAFC plant pathologist said during the most recent Beef Cattle Research Council webinar on identifying and managing forage diseases.
Baling or ensiling wet plant matter can make problems worse, she said. The confined, wet environment creates a breeding ground for fungi, some of which may produce dangerous chemicals for livestock eating the feed.
“When you’re talking about, for example, ensiling, you’re expecting a natural fermentation process to happen,” she said. “However, if there is more moisture there than there should be, the organisms that are responsible for the actual fermentation won’t necessarily end up being the major species that ends up being there. First of all, you might not get proper fermentation, so you might not get proper preservation of the plant, but you can also get spoilage happening.
“That can be kind of an insidious problem, especially if you’re feeding from, say, a bunker or a siled bale,” she added. “That’s because it can be really difficult to examine the entire face surface and you might not realize that there’s a centre of rot that’s taken hold.”
The problem can crop up after samples are taken to verify nutrient value, webinar attendees heard.
Stop the spoil
In general, Jewell advised reducing surface leaf moisture (for example, timing irrigation so that moisture burns off in the hottest part of the day) and proper drainage in the field.
Farmers should choose resistant varieties according to local disease threats, while rotated annuals will help avoid building disease reservoirs, webinar viewers heard.
Resistance is only beneficial if there is a clear threat of that disease in a farmer’s region, Jewell added.
“If a plant is resistant to a disease, it’s resistant because it’s likely making something extra,” she said. “So, for example, it might be making a defensive enzyme that’s going to allow it to attack that pathogen when that pathogen tries to attack it, but there’s a cost to making that extra enzyme. So, if the plant is always sort of on high alert, looking out for this pathogen, it’s kind of stressing itself out, and if that stress is never there, you’re actually going to get a lower yield than if you planted a susceptible cultivar.”
The fight against fungi may also mean stepping away from the fertilizer tank. Beyond poor application timing — a late fertilization may keep plants growing when they should be getting ready to go dormant, at the expense of the first cut the following year — Jewell noted the fungi also need nitrogen and may get more food from fertilized fields.
“You may be thinking that you’re fertilizing to encourage the plant to grow and fight back, but what may be going on, depending on the specific pathogen that’s there, is you’re just giving that fungus a delicious, healthy green salad to munch on,” she said.
Local disease issues
Manitoba producers are likely familiar with rust’s orange, powdery spores or the dicolouration heralding snow mould.
Alfalfa may face black stem (marked by expanding dark spots on a plant’s lower leaves), leaf spot and downy mildew or verticillium wilt (causing yellowed and wilting foliage and dry tissue in the root), according to Manitoba Agriculture’s forage disease fact sheet.
Ergot, noted for dark structures in the seed head and infamous for its dangerous toxins, has been known to crop up in the province’s cereal crops, including any grown as part of a forage mix, Manitoba Agriculture says.
Purple spot, commonly found in Timothy grass and named for its bull’s-eye pattern, is less dangerous, although it has been linked to light sensitivity in animals, Jewell said.
Glen Friesen, forage specialist with Manitoba Agriculture, named root rots as one of his top disease risks.
“Aphanomyces is one that I think we’re seeing,” he said. “People just generally think that stands sort of time out — they age and they time out… the crown dies due to age — but more often than not it’s a disease in the crown that is causing the problem.”
The “water mould,” so named for its actively swimming spores, draws more attention during the wet conditions that allow it to spread.
Dave Koslowsky, chair of the Manitoba Forage and Grassland Association, says most Manitoba farmers are more concerned with insects like alfalfa weevil than fungi.
“That varies from year to year,” he said. “Conditions have to be just right for it.”
There are a “sprinkling” of other diseases on the association’s radar, although there were few threats this year with the dry season, he said.
Cutting out disease
Most hay stands are cut before a disease can really take hold, Friesen said, and an early cut is among the most common forage disease management advice given to producers.
“If you were planning to cut in a week from now and you’re looking out over your beautiful alfalfa field and you see that there’s a disease outbreak on the go and there’s a high chance that you’re going to start seeing defoliation soon, the reduction in yield and nutrient value that you’re going to see from cutting a little bit earlier than you would have liked to is going to be worth it if you cut it before the disease becomes very severe,” she said.
Disease is a greater threat for forage seed growers, Friesen added, since plants reach full-season growth before harvest.
Roger Burak, research manager for the Manitoba Forage Seed Association, singled out three main disease threats, the sclerotinia-like blossom blight, leaf spot and black stem.
Winterkill and snow moulds, which would affect a regular forage stand, would also cross over into seed, he said. Aphanomyces, however, is not a major concern for the Manitoba Forage Seed Association.
The association hopes to see forages added to more fungicide labels, something Burak says is an ongoing challenge for producers who do face disease pressures.
“Because forage and forage seed is kind of a minor crop, a lot of the herbicide companies don’t put them on their label,” he said. “They put the major crops on their label, so really, even for us to combat a lot of diseases, there’s not a lot of registered products available to us.”
The Manitoba Forage Seed Association hopes its own research will inspire further testing.