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Grassy weed control essential for small grain yields

Who would have thought small grains would jump to near the head of the class of economically attractive field crops in the rarified world of ag today when just about everything is hitting a home run?

Strong prices have made small grains the second largest acreage field crop in the state with an estimated 750,000 acres seeded this season.

Not only are prices appealing to growers, but small grains carry less risk than many other field crops.

“Durum wheat has taken the lead right now,” says Steve Wright, Tulare County UC farm advisor at the recent California Weed Science Society annual meeting in Monterey.

“Triticale acreage has also picked up quite a bit as well. Right now growers are getting about $300 a ton for Durum wheat and $280 a ton for small grains. They’re getting up to $42 a ton for small grain silage, so there is a lot of interest and opportunity to make money with small grains right now.”

Taking full advantage of that profit potential, however, requires some attention to competition from yield and quality-robbing weeds.

“When wheat was running about $132 a ton, you had to make at least three tons to the acre to make money,” Wright says. “Now that it’s approaching $300 a ton, you can make money at almost any yield.”

For an investment of only $15-$25 an acre for weed control, including aerial application costs, growers can gain a substantial return. That’s particularly true in irrigated wheat where weed control costs represent only about 5 percent of the total production costs. In dryland wheat, weed control can account for as much as 10 percent to 20 percent of production costs, making it a little more difficult to justify if it does not rain to produce yield and a return on the weed control investment.

The primary weeds of concern in small grains include wild oats, Italian ryegrass and canarygrass. Wild oats is the predominant weed problem in the Southern San Joaquin Valley. Canarygrass, based on a survey of acreage, is the overall No. 1 small grains weed problem in California, particularly in the Imperial Valley. Other problematic weeds in small grains include annual bluegrass which is increasing. Ripgut brome and foxtail are also a concern, particularly in situations where growers are converting old pasturelands to wheat production.

“Much of our weed problem in the San Joaquin Valley is attributed to the dairy situation and spreading un-composted manure on fields,” Wright says. “There are a lot of weeds that come through these manures when they are spread at a rate of 5 to 15 tons per acre.”

The seed bank from using manures as fertilizer has led to an exponential increase in weed problems in many areas. It can be staggering. One wild oats plant per foot equals 43,500 plants per acre.

“If each plant produces 200 seeds and 60 percent of them shatter and reach the soil, you’ve got a potential reseeding rate of 5.2 million seeds per acre,” Wright says. “If you have 10 wild oats plants per foot, it’s not only going to reduce your yields significantly, it’s also going to reduce your bushel weight.”

That yield loss could be as much as 20 percent or 600 pounds per acre, according to Wright. Additionally, dockage penalties on top of that can translate into another 5 percent loss.

Competition studies conducted in 1977 by Jim Hill, UC Davis weed scientist, have shown that even one wild oats plant per foot can reduce yields enough to make a herbicide treatment cost effective in irrigated wheat.

Wheat density can affect the impact of weeds on production. “The most common wheat density we like to shoot for is 35-38 plants per foot,” Wright says. “Lower density wheat stands will be more impacted by wild oats.”

Additionally, the timing of wild oats emergence greatly influences the impact, according to Wright. Wild oats that emerge before or with the wheat will have a much greater impact than wild oats that come after the stand is established.

“Anything you can do to get a jump on weeds will help,” Wright says. “If it’s possible to plant into rain moisture or a pre-irrigated fields, that will help reduce the impact of weeds that compete with the wheat.”

Monitoring fields early is important to stay ahead in controlling weeds. There are opportunities this season for growers to take advantage of a new herbicide, Prowl H2O, which should be registered shortly, according to Wright.

“Wild oats have a primary and secondary dormancy,” he says. “If you go in there too early, you’re going to miss that second flush.”

That’s an important consideration when dealing with heavy wild oats pressure.

Timing is very critical for wild oats control because even if control is 95 percent, 15 plants per foot will result in a tremendous seed bank that can come back to bite you.

“Puma does a great job of controlling wild oats and canarygrass from the two-leaf all the way to the two-tiller stage,” Wright says. “In general we get the best control by going on the late side. We’re looking at adding Prowl H2O to that mix to pick up some of those late emerging weeds.”

Although Shark offers good control of grasses, it cannot be tank mixed with most other grass herbicides. Achieve does a good job on canarygrass, according to Wright. Axial is another grass herbicide with a promising fit (not yet registered), while Treflan is an old standby as a preplant incorporated material for suppression of wild oats and canarygrass.

“Prowl H2O will help complement some of our programs,” he says. “It’s been very successful in Arizona, particularly where they can plant into moisture and then apply the product. Eventually it needs to be incorporated by rainfall or irrigation.”

Other options offer a wider spectrum of control that may be desirable depending on the weeds present.

“Osprey is another broad-spectrum material that picks up annual ryegrass, canarygrass, wild oats, annual bluegrass, and ripgut and has some good broadleaf suppression,” Wright says. “It does have a plant back issue that still needs to be worked out, and it does cause more yellowing than the other herbicides. Osprey also picks up cheeseweed and does a great job on chickweed, a growing problem in the San Joaquin Valley.”

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