Growers planting Roundup Ready alfalfa for the first time this year can reduce their seeding rates, say two Extension forage agronomists who have worked with the biotech crop.
Putting down fewer pounds of seed will help lower the cost of the system that Dan Undersander, University of Wisconsin, and Dan Putnam, University of California, say delivers simple and effective control of most weeds, including species that escape other herbicides.
They expect fairly wide adoption of the technology in their states, especially among growers dissatisfied with their current weed-control programs.
The cost of Roundup Ready seed is the primary deterrent. But glyphosate is less expensive than other herbicides used on alfalfa, and it doesn’t set the crop back like some do. So Roundup Ready growers may harvest slightly higher first-year yields, say the two agronomists.
Their lower-seeding-rate recommendation may be an equally meaningful cost cutter. Wisconsin studies have shown that, due to glyphosate’s better weed control, 10-12 lbs of Roundup Ready alfalfa seed per acre is adequate, Undersander reports.
“So one of the options is to buy the higher-priced seed and keep your costs down by getting four acres per bag instead of three,” he says.
With conventional alfalfa, Undersander recommends 12-15 lbs/acre, a rate Putnam says should suffice for Roundup Ready growers with good management in California, where much higher rates are the norm.
“There’s no question that a grower who’s currently putting 30 lbs of alfalfa seed down in his fields, which a lot of our growers do, can back that seeding rate off pretty significantly,” says Putnam.
“A lot of times, growers use high seeding rates to make up for sloppy stand establishment methods,” he adds.
To get thick stands with lower seeding rates, they’ll need to plant at the right time for optimum germination; prepare smooth, firm seedbeds; and adjust seeders to place seed at the right depth with good seed-soil contact.
“If they pay more attention to those three things, they can back down on their seeding rates pretty successfully,” says Putnam.
Properly timing the glyphosate application is the next critical step. Strictly a contact herbicide, it should be applied after most weeds have emerged but when they’re small. The label says to spray when alfalfa’s at the three- to four-leaf stage, and both agronomists say that’s about right.
“I would even go with the three-leaf stage to try to get the weeds at a small stage,” says Undersander.
A single properly timed glyphosate application will kill most weeds plus the 5-10% of alfalfa plants that don’t have the Roundup Ready trait. It’s important to remove those plants, as well as the weeds, during the establishment period, say the agronomists.
In Wisconsin, most Roundup Ready alfalfa fields likely will be sprayed just that one time. Undersander says weed control more than 60 days after seeding doesn’t increase yield, so it doesn’t pay, except for commercial hay growers who get premiums for pure alfalfa.
“For the dairyman, it’s probably not going to be worthwhile ever to apply herbicide after the establishment period,” he says.
Growers who prefer alfalfa-grass mixes aren’t out of luck with the Roundup Ready system, he adds. They can seed pure alfalfa, use glyphosate to get a clean stand, then add a grass. The second seeding can be done shortly after the glyphosate application, if soil moisture is adequate, or that fall.
Roundup Ready alfalfa can be established with a nurse crop, too, if one is needed to prevent soil erosion, dry out wet soils or shield alfalfa seedlings from wind. The grass companion crop would be removed early by the glyphosate application.
That system was tested in Minnesota several years ago, with Poast Plus as the herbicide, Undersander reports.
“One of the reasons that didn’t take very well is because at times, particularly under dry conditions, broadleaf weeds came in and Poast Plus wouldn’t control them. Now if we plant Roundup Ready alfalfa, we can use a short-term cover crop, either oats at 1 bu/acre or Italian ryegrass at 2 lbs/acre.”
The scenario is different in California, where growers typically direct-seed pure alfalfa on flat land and often use herbicides on established stands as well as during establishment. Putnam says glyphosate’s crop safety and wide application window give growers more weed-control flexibility.
“You can apply two treatments, if needed, if you have a particularly severe infestation either during that early growth period or another period,” says Putnam.
He says Roundup Ready alfalfa may not make sense for growers whose current weed-control strategies are working well. But those with troublesome weeds like nutsedge, dodder, common groundsel or fiddleneck will have better luck controlling them with glyphosate than with the other weed killers currently available.
“We have some really tough weeds here, and Roundup Ready is a pretty exciting technology for some of them. However, we have to remember that it doesn’t control all weeds, and weed resistance could occur, which is why growers need to use an integrated approach, rotating herbicides with Roundup.”
If weeds are controlled early, the need for future herbicide applications may be reduced, he adds.
“The most effective weed-control strategy is a very good, vigorous stand of alfalfa,” says Putnam. “Any weed scientist will tell you that. So the key issue is what happens during that stand establishment period.”