Weed Control in Rice Fields

Controlling Herbicide-Resistant Weeds in California Rice Fields

By Emily McKay Johnson, Associate Editor

Whitney Brim-DeForest, UC ANR Cooperative Extension rice farm advisor for Sutter, Yuba, Placer and Sacramento Counties in California, currently works in all rice production areas across the state to identify problematic weeds in rice fields.

Given her background in weed science, Brim-DeForest explained California rice growers flood their fields for weed suppression, as well as use herbicides for weed control and management. “I’d say that we do have quite a few herbicides right now. As we continue to get new herbicide resistant weeds every year,” said Brim-DeForest, “we are starting to run out of options, especially for some growers who encounter herbicide resistance.”

Brim-DeForest believes herbicide resistance was first discovered in the early 1990’s, but “has become significantly problematic for growers within the last 20 years. Because of the herbicides we use and the limited number that we have, we have ended up with an increasing number of weeds that are herbicide resistant every year. Since about 2000,  we’ve had a new species or herbicide that encounters resistance every year,” she stated.

Brim-DeForest treats a multitude of weed species in her line of work. “I would say the watergrass species is our biggest problem,” she noted. “We also have a weedy red rice that was discovered in the early 2000s. It is not widespread, but we do have a few fields with it,” she explained.

Featured Photo: Whitney Brim-DeForest, UC ANR Cooperative Extension rice farm advisor.

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Tips on Minimizing Herbicide Drift

Its critically important to minimize drift when applying crop protection materials.

Alan James is a Technical Services Agronomist with Mid Valley Agriculture Services, based in Linden, in Stanislaus County. James noted the usual drift issue.

“We get called out all the time by the growers themselves, ‘What are those spots on my leaves?’ and eight times out of ten, it’s drift from the herbicide application they put on, on their own. There is always a little bit, you can’t eliminated drift, you can minimize it,” said James.

James points out some practical strategies in minimizing drift, and not just the obvious of not spraying during heavy wind.

“They need to think about the type of nozzles, the 800 nozzle produce fewer finds than the 110 nozzles, and they came out a few years ago with an extended range, T-Jet extended range nozzle, which allowed you to work at lower pressure and still the coverage,” said James. “And since then there has been at least 2 types of air induction nozzle, where you draw air in, and produce droplets that are bigger because they are wrapped around a little bit of air, and they tend to settle quicker,” he added.

Low pressure is the key, says James.

“You get a good pattern with 15-20 PSI, which produces much fewer finds if you are up at 30-40 PSI. and sometimes they think the higher the pressure the better ill drive it down into the weed, and that has nothing to do with that, it just producing more finds.” said James.

James comments on the scenario of worn out or missing nozzles.

“Every year, you ought to start out with a new set of nozzles, and make sure they are all the same. That is the other thing, when they have weed sprayers got 8 nozzles across the boom, and one plugs up, they have to put in the that plugged one, whatever they got in their pocket. which may or may not be the right size.” said James.

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Ranchers Concerned About Invasion of Medusahead Weed on Foothill Rangeland

Source: Jeannette E. Warnert

One of the worst rangeland weeds in the West is aptly named after a monster in Greek mythology that has writhing snakes instead of hair.

Medusahead, an unwelcome transplant from Europe, is anathema to the cattle living off rangeland grass. The weed’s three-inch-long bristles poke and sometimes injure the animals’ mouths and eyes.

The weed is also low-quality forage for livestock. When medusahead takes over rangeland, it reduces the forage value by 80 percent.

When Fadzayi Mashiri, UC Cooperative Extension advisor in Mariposa, Merced and Madera counties, was appointed in 2013, she became the first natural resources and rangeland expert to hold the position since the retirement of Wain Johnson more than a decade before.

She polled local ranchers to determine their most pressing problems. They said weed management, and in particular, medusahead.

Medusahead is relatively easy to identify on the range. It has distinctive stiff awns and a seed head that does not break apart as seeds mature. Patches of medusahead are obvious when spring turns into summer.

“Medusahead stays green after most of the annual grasses have dried off,” Mashiri said.

Medusahead has high silica content, making it unpalatable to cattle. The silica also protects the plant from decomposition, so a thick thatch builds up on the rangeland, suppressing more desirable species, but not the germination of the next year’s medusahead seedlings.

Over the years, UC scientists have discovered a number of medusahead control strategies:

  •  Corral cows on medusahead before the plant heads out or employ sheep to graze medusahead patches. It’s not sheep’s favorite forage either, but they will eat if left with no other option.
  • Prescribed burning in late spring or early summer. However, this strategy poses air quality and liability issues.
  • Apply nitrogen fertilizer to medusahead to improve palatability before it flowers, which is showing promise for controlling the weed and boosting the value of infested rangeland.
  • Chemical control.

In spring 2014, Mashiri conducted a demonstration field trial in Mariposa County of medusahead control with the herbicide Milestone, which was developed by Dow AgroSciences mainly to control broadleaf weeds like yellow starthistle.

The trial followed rangeland weed control research done by scientists including Joe DiTomaso, UC Cooperative Extension specialist in the Department of Plant Sciences at UC Davis. DiTomaso found that the density of medusahead in treated areas declined and concluded that Milestone prevents medusahead seedlings from thriving.

Unfortunately, Milestone treatment of large rangeland areas is expensive.

“But if the value of forage declines, the productivity of livestock is compromised,” Mashiri said. “When you look at it that way, the chemical treatment might be useful.”

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