Let Oats Control Weeds

“Research shows if you have three wild oat plants per square foot and seed at about 50 pounds of seed per acre, you

can expect a 22 per cent yield loss. If

you increase the seeding rate to 120 pounds of seed per acre, your yield loss will be reduced to 11 per cent.”

—STEVE SHIRTLIFFE

Don’t underestimate the potential of proper cultural practices in controlling weeds in oats, says a University of Saskatchewan researcher. Get the crop seeded fairly early, use a proper seeding rate, and get the crop growing before the weeds emerge, says Steve Shirtliffe, an associate professor of field crop agronomy and weed ecology.

“Producers tend to think if they don’t have a herbicide for a particular situation, there isn’t much they can do,” he says. “But proper cultural practices like timing of preseeding burnoff, seeding rate, and selecting for large seed size can produce a large cumulative benefit.”

Oats, generally, are quite a competitive crop. They fall somewhere between wheat and barley for weed competitiveness, Shirtliffe says. The key, he says, is to get the crop growing even two or three days ahead of weeds such as wild oats.

Timing of the pre-seeding burn off is important. “Seed as soon after the pre-seeding treatment as possible,” he says. “If you let a week or more go by you can have weeds beginning to emerge. If there are three wild oat plants per square foot, a farmer would consider that a fairly dirty field. And it can have a significant impact on yield.” Shirtliffe says he has seen wild oat infestations range from 10 to even 100 weed plants per square foot.

SEED EARLY, NOT LATE

You want to seed oats fairly early, particularly if you’re after the high quality milling oat market. “There is general belief you can seed oats almost anytime, or in some cases some growers feel that later is even better,” he says. “But if you want high quality milling oats, seed early. Get the crop growing and maturing before that critical period in first or second week of July when you are going to see more rust developing or run the risk of high heat, which can really affect seed quality.

“If you are just growing oats for green feed it is not an issue, but if you hope to have milling oats, earlier is better.”

Some farmers think seeding later it is better because they miss the competition of wild oats. Wild oats tend to have their first flush earlier in May and will go dormant later on. But with timely seeding you’ll get the crop growing ahead of the weeds, and wild oats won’t be an issue.

PLUMP SEEDS EMERGE FASTER

Seed size is an important factor, too, says Shirtliffe. “Select seed with big plump seeds or have your seed cleaned so you are seeding with big plump seeds,” he says. “With those plumper seeds, you get faster emergence and just have a much more healthy vigorous crop that not only competes better with weeds, but is more likely to produce high quality seed for the milling or pony oats market.”

If a producer is using thinner seed, increasing the seeding rate does help, but he says plants from smaller seeds just don’t have the competitive strength as seedlings produced from plump seeds.

UP YOUR SEEDING RATE

Seeding rate is critical for getting enough plants in the ground. “A lot of farmers seed according to so many bushels per acre, but that practice can have real limitations,” he says. “Some of the older oat varieties weighed about 30 pounds per bushel, while some of the newer ones are 40 pounds per bushel or more. If you follow a standard 1.5 bushel per acre seeding rate, you could be seeding anywhere from 34 pounds to 50 pounds of seed per acre, depending on the variety.”

Shirtliffe recommends that producers do a square-foot seed count to see what is actually going in the ground. With good quality plump seed, and moderate wild oat numbers, he says producers should aim for about 25 seeds per square foot. That’s roughly 80 pounds per acre.

If there’s a risk of a higher level of wild oat numbers, increase the seeding rate to achieve about 37 seeds per square foot, which represents about 120 pounds of seed per acre.

“Research shows if you have three wild oat plants per square foot and seed at about 50 pounds of seed per acre, you can expect a 22 per cent yield loss,” he says. “However, if you increase the seeding rate to 120 pounds of seed per acre, your yield loss will be reduced to 11 per cent.”

Shirtliffe says on average 60 to 80 percent of seeds planted survive.

Seed early, with good quality plump seed and get the seeding rate up, he says. “Oats are very good at competing against wild oats, but the key is to get the crop growing ahead of the weeds,” he says. “If the crop has a head start and has a good density it will keep weeds controlled, but on the other hand if the weeds have a head start they will have an effect on yield.”

Shirtliffe says, in a worse case scenario, if producers do end up with an oat stand with high wild oat numbers, one last option for keeping weed seeds out of oat samples is to combine the crop later. Wild oat seeds will shell out in early fall, so if the producer can wait a couple weeks to swath or straight combine, most of the wild oat seeds will be on the ground.

CONSIDER CROWN RUST CONTROL

Depending on the growing season, growing region and variety, Shirtliffe says most oat producers should be prepared to treat crops with a fungicide to control crown rust.

A Saskatchewan Agriculture fact sheets says the highest risk areas for crown rust is in Manitoba and southeast Saskachewan. Late planting of oats followed by humid warm weather are the most favourable conditions for disease development. Some oat cultivars bred for resistance to crown rust are no longer effective at warding off infection. That’s because the rust population has developed new races that have overcome the resistance. Because of this breakdown in varietal resistance, growers in high-risk areas will need to switch to newer resistant varieties or incorporate other management practices to reduce disease risk. Do both for even more protection.

The rust pathogen is not seed or soil borne. The primary means of infection is from rust spores moving up on air currents from the southern part of the United States. Onset and severity of rust infection in the eastern Prairies depends on what happens on southern crops.

Within the rust fungal population, there are a number of different “races” that developed and are specific to oat varieties carrying certain rust resistant genes. Most oat varieties currently grown on the Prairies rely on a single gene for resistance: Pc68. The outbreak of oat rust in 2005 proves this gene is no longer effective.

As of 2009, three varieties offer some resistance to crown rust. Leggett and HiFi are rated as very good resistance. Triactor is rated as good resistance. Breeding for crown rust resistant varieties is ongoing.

Other than using resistant varieties, one of the key ways to avoid severe infection is to plant oat crops early. The premise for planting early is that the crop should be advanced enough by the time rust spores arrive on the eastern Prairies. These crops will not suffer significant yield or quality loss.

Foliar fungicides are another tool. Fungicides registered for crown rust on oats include the propiconazole products Tilt 250E, Bumper 418EC and Pivot 418EC. Stratego 250EC (propiconazole and trifloxystrobin) is also registered.

The ideal timing for application is to spray at flag leaf emergence. Rust can develop very quickly, so earlier application may be necessary if conditions are conducive to rapid spreading of the rust. Once the flag leaf is covered with spots, it is too late to apply fungicide. The decision whether to apply fungicide must take into the account the availability of rust spores moving up from the south, and weather conditions. Spraying fungicide will not be necessary in all years or locations.

—Lee Hart is a field editor for Grainews in Calgary, Contact him at 403-592-1964 or by email at [email protected]

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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