Rice Farming

Sock It To ’Em

Alternating rice systems can help control
problem weeds in California

By Brenda Carol

Weeds can cost a California rice producer anywhere from $75 to $150 an acre, and that figure can skyrocket if resistance becomes an issue. With limited herbicides available to solve weed problems, researchers have been conducting trials for the past four years to see how effective cultural practices, such as rotating rice establishment systems, will work.

Traditionally, in California, growers have used conventional water seeding for stand establishment. However, studies have shown that alternating to drill seeding or other production systems periodically can help control problematic and even herbicide-resistant weeds.

“Research has been going on at the Rice Experiment Station since 2004 to evaluate the use of stale seedbeds in water- and drill-seeded rice systems,” says Albert Fischer, weed scientist at UC Davis.

Several different production scenarios have been studied as part of the Alternative Cropping Systems Project at the Rice Experiment Station and are still ongoing. They include:

1. Conventional water-seeded
2. Conventional drill-seeded
3. Water-seeded with stale seedbed
4. Water-seeded, minimum-till, stale seedbed
5. Drill-seeded, minimum-till, stale seedbed

One of the issues researchers have been evaluating from switching among various production systems is the effect on yield potential.

“Four years of research have shown that the yield potential of each of these five systems is similar,” Fischer says. “Stale seedbed systems have demonstrated potential for good yields while drastically altering the weed species that emerge with rice.”

Alternating systems helps shift weed spectrums
The majority of California’s rice production is some form of a water-seeded system that favors aquatic weeds. By alternating a traditional water-seeded system with a drill-seeded system, growers can shift the weed spectrum toward non-aquatic weeds. In water-seeded (anaerobic) systems, aquatic species, such as sedges and broadleaf weeds, quickly take over.

“In a continuous-flood rice system, weeds such as barnyardgrass and sprangletop are suppressed,” Fischer says. “Drill-seeded rice, on the other hand, is less favorable to aquatic species and helps growers manage those weeds that have become problematic in the anaerobic systems.”

In the stale seedbed system, weeds are allowed to germinate in the top inch of the soil where they can be controlled with broad-spectrum herbicides, such as glyphosate or pendimethalin.

Dealing with herbicide-resistant weed populations
Alternating stand establishment systems also enables growers to combat herbicide-resistant weeds that have become a significant problem in California’s rice monoculture. Approximately 80 percent of California’s rice acreage remains in rice year after year simply because there are no other rotational options, according to Chris Greer, Sutter and Yuba County Farm Advisor.

Managing weeds in continuous rice can be quite tricky when resistance becomes a problem. “You get into a fairly extensive weed control program trying to kill resistant weeds,” Greer says. “You may have to make multiple applications and may not even kill the weeds. You’ll just knock them back. In some cases, the resistance is so bad that the herbicides don’t work very much at all anymore.”

Herbicide resistance has been documented in a number of different broadleaf and grass weed species that infest rice fields, but it is not consistent across the entire acreage.

“There could be different populations of weeds that are resistant to different herbicides depending on what the grower has used in the past,” Greer says. “The problem is that sometimes they may find that one herbicide works really well – perhaps on watergrass – so they continue to use that herbicide year after year. Ultimately, of course, they will end up with resistance and not even have that herbicide option anymore.”

How does this approach pencil out?
The economics of alternating among different systems can get complicated and depends largely on what a grower chooses. Going from a conventional water-seeded program to a drill-seeded program does not really require much additional investment, and some of the costs are offset just because operations can be piggybacked, according to Greer.

The only additional investment is a drill, which may range somewhere from about $40,000 for a used one up to $100,000 or more for one with all the bells and whistles. Even so, it’s relatively inexpensive considering the enhanced ability to control tough weeds over the long haul.

“Say, for example, you go with a no-till program, you will do the groundwork in the fall to get everything level,” he says. “Then, in the spring, you don’t have any groundwork, so you can actually save money. Let’s say you’re doing a no-till-in-the-spring, water-seeded system, the only thing you’re going to do in the spring is flush when it’s warm enough to get the weeds to come up, hold the water for 10 days, drain the field and spray the weeds with glyphosate. Then in a couple of days, you can reseed and flood. With a drill-seeded system, you are going to have the cost of a drill, but you’re not paying the airplane for seeding.”

Depending on the rig and how it’s set up, costs can further be reduced by applying starter fertilizer at the same time. “Economically, I don’t think there are any real issues there,” Greer says.

Be aware of benefits as well as potential problems
Only about one or two percent of California rice is drill-seeded at this point.

“We see more guys going to drill-seeded systems, but it’s slow,” he says. “Those are the type of systems that favor things like red rice, which we definitely don’t want. I think there are some benefits to the system, but there are also some potential problems that we could run into.”

It’s a given that alternating production systems requires a better understanding of herbicides and how they are used in the different systems. Level fields and timely, well managed irrigation is critical. Alternative rice systems may be one of the answers the industry has been looking for to combat resistance and retain the efficacy of its limited herbicide arsenal.

Brenda Carol is a freelance writer based in California. Contact her at (805) 226-9896 or brenda@brendacarol.net.

New herbicide for dry or drill-seeded rice in California

Because California rice culture has historically been largely water-seeded, the use of pendimethalin (the same active ingredient in Prowl herbicide) on rice in California has been limited at best. Because pendimethalin is a pre-emergent root inhibitor, its use on pre-germinated, surface water-seeded rice is phytotoxic.

Therefore, the use of pendimethalin on rice in California must be on dry or drill-seeded rice. A new adhesive formulation of pendimethalin (Harbinger) allows the herbicide to be applied before the initial flush. Harbinger was registered in 2008, and at this time, is only registered in California. Dave Sills with Crop Production Services (formerly Western Farm Service) holds the patent on the formulation.

In addition to being a broad spectrum soil-active herbicide, Harbinger will control junglerice and sprangletop in rice, according to the label. For more information, call (800) 829-7671.

Source: Crop Production Services


California Rice Research Board

UC Cooperative Extension Rice Project