Don’t Let Them Up

Don’t Let Them Up

The best weed control recommendation out there continues to be “don’t let them come up.” Overlapping residuals is the consistent theme of weed control recommendations in rice, especially for grasses.

We certainly want to properly utilize burndown herbicides to begin with a clean slate, but from there, our residual herbicide chemistry needs to be the focus. When evaluating herbicide costs and various programs, those that lean on using our available herbicides that provide pre-emergence control make the budgets look the best.

Command continues to be a foundational herbicide, but we need to look closely at how we incorporate Prowl, Bolero, and Facet for grass control as well. Prowl and Bolero have the wrinkle of being delayed pre-emergence products but are an excellent fit shortly after planting to mid-post to continue our weed control.

Facet has a wide window of use, and while some of it’s post-emergence, grass control may not be as effective anymore. However, it still has a significant role to play as a pre-emergence herbicide even on many of our barnyardgrass populations that are resistant to it as a post-emergence product.

Other products such as Sharpen, Gambit, and League can also serve us well as pre-emergence herbicides but vary depending on weeds we need to control.

Clearfield and FullPage systems can utilize additional residual activity from Newpath or Preface. Remember if you utilized those products last year, you cannot plant conventional rice or Provisia / MaxAce rice this year, or carryover will give us issues.

Speaking of Provisia and MaxAce, these products do not offer residual weed control. But note that we now recommend a Provisia program of 10 ounces early POST followed by 10 ounces mid-POST, followed by 11 ounces post-flood. Our recommendations for MaxAce remain the same with 15.5 ounces Highcard early POST followed by 15.5 ounces Highcard mid-POST and flood immediately. If you grew Provisia or MaxAce last year, rotate to soybean this year to avoid outcrossing.

Remember that planting into a stale seedbed environment helps to improve our overall rice stands but also minimizes weed emergence. Get the ground slick and leave it alone to limit weed emergence in the first place.

Rice budgets, and other crop budgets, continue to get tighter. Focusing on early season weed control and our residual herbicides will help us limit the more costly post-emergence herbicide applications later, which may be a key in skimming by this year. At a certain point, we just need to let weeds go, save the money, and live to farm another day.

Early Season Weed Control is Where it Matters Most

Weed competition has been studied extensively throughout history and most of that research has suggested early season weed management is where it matters most regardless of crop. Early season weeds tend to be more competitive with crops, especially rice, meaning this is the most important time to be aggressive with herbicides. As a matter of fact, this rice weed scientist turned specialist will tell you there’s never a time to not be aggressive with herbicides prior to flooding.

When we talk early season weed management in rice, we’re typically talking about grasses like barnyardgrass, Amazon sprangletop, and broadleaf signalgrass. Like all the other rice-growing states, barnyardgrass remains the No. 1 herbicide issue in Texas rice.

Unfortunately, in 2024, we were able to confirm more barnyardgrass resistance to multiple modes of action across the Texas rice belt. It’s nothing new, especially with regards to propanil, but the issue is growing, and we are losing additional modes of action like Newpath, Regiment, and Facet at a rapid pace.

Clearfield rice has long been the gold standard for weed control in rice, with the ability to use Newpath and Beyond in addition to all the other herbicides labeled in rice. Historically, Clearfield rice has been a three-shot system, with two applications of Newpath early and one application of Beyond later in the season.

In addition, Newpath has excellent residual activity. That being said, Clearfield rice just isn’t cutting it in some areas of Texas these days. As a proud Louisiana State University alumnus, it hurts my heart to say that, but the system has been fantastic for 20 years and really has changed the way we grow rice, especially in Louisiana.

I am encouraging growers to utilize Provisia or MaxAce varieties and apply quizalofop where their barnyardgrass issues are the worst or where the Clearfield system is starting to slip. The quizalofop-resistant systems provide some of the best grass control I have ever seen in rice when used correctly.

Unlike the products used in Clearfield rice, quizalofop only works on grasses, has no residual, and calls for a two-shot program instead of three. Additionally, quizalofop is highly susceptible to herbicide antagonism. One of my favorite rice projects I have done thus far was my master’s, where we looked at most of the tank-mix options available in Provisia rice, as well as timings of applications with antagonistic mix partners.

Because of the above-mentioned differences in Clearfield and Provisia, growers should be ready to make some pretty significant changes to their herbicide programs and be ready to part with some products they have grown accustomed to using. In my master’s project, we learned that many of the products we love today might not be a good fit in quizalofop-resistant rice. The “big three” to avoid are Regiment, Grasp (and Grasp Xtra), and propanil. For what it’s worth, you can throw 2,4-D in that mix as well. I think the pictures below tell the story much better than I can.

If utilizing Provisia rice, I would encourage growers to overlap residuals like Sharpen, Gambit, or League for broadleaf or sedge control; that way, we don’t have too many things going in the tank when quizalofop application time arrives. Most important, it is extremely beneficial to include one of these products in the pre-emergence application with Command, potentially eliminating a broadleaf tank-mix partner from the first quizalofop application. Use Sharpen where pigweeds are present.

If a tank-mix is necessary in the first application, Permit at no more than an ounce has proven to be a solid mix partner with quizalofop. We also saw good results and little to no antagonism when we mixed it with Loyant, Basagran, Aim. In addition, Bolero or Prowl are also good options for growers who are wisely wanting to overlay residuals with their first post-emergence quizalofop application. The second shot should always be applied alone, and both the first and second applications have looked great for me with a high-quality crop oil like concentrate like Agri-Dex at 1% volume/volume.

If you are in a situation where an antagonistic mix partner needs to be used, our work suggested the quizalofop should go out first and at least 24 hours prior to the broadleaf product. I prefer several days before the broadleaf application just to be on the safe side, but any time up to 24 hours before should be fine.

In addition, growers should be aware that applying quizalofop in cloudy weather can lead to significant injury issues. For those who aren’t utilizing quizalofop-resistant technology, always remember overlapping residuals prior to flooding is a great enhancement or alternative to the postemergence products we are using, especially those post-emergence grass products that don’t work too well without a permanent flood on the field.

Get a Head Start on Weed Control

California rice farmers are facing greater problems each year in controlling watergrass species. This is in part due to the spread of a new species (coast cockspur) but also due to the increasing number of fields with resistant biotypes of all watergrass species (barnyardgrass, late watergrass, and early watergrass). New products are coming down the pipeline, but in the meantime, the best way to combat these grasses is to have a plan going into the season, instead of trying to deal with grass control late in the season.

In the worst fields, a stale seedbed can be a good option. The purpose of a stale seedbed is to bring up weeds prior to rice planting, which can then enable the use of a non-selective herbicide such as glyphosate or capric/caprylic acid. A stale seedbed can also work in a year when it rains late or after tillage. A flush of water, whether from rain or irrigation, and a week of warm weather can bring up a large number of watergrass plants.

Past research has shown that as much as 90% of a population can emerge in about 10 days (this varies somewhat according to temperature). Many growers do not like using a stale seedbed as it can delay planting, but it can be a good option for rotation on one field at a time, to try to clean up a field. Work with your local Farm Advisor for the best timing and for guidance on application rates.

If a stale seedbed is not a possibility, it is important to use multiple modes of action at the beginning of the season. Many watergrass biotypes have widespread resistance to granular herbicides, particularly those containing thiobencarb, benzobicyclon, and penoxsulam. Some fields may also have clomazone resistance, but it is less widespread. The best solution is to combine modes of action to attempt to overcome resistance. Resistance in watergrass species in California is metabolic, meaning that the plant can break down, or “metabolize” or “eat” the products, detoxifying them within the plant system, rendering the herbicides ineffective. 

The positive part of having metabolic resistance is that unlike target-site resistance, it can be overcome, usually through increased rates and/or combinations of products either applied in close succession or at the same time. Some combinations that are popular and work fairly well for watergrass control are: pyraclonil and benzobicyclon, clomazone and benzobicyclon, and clomazone and thiobencarb (not an exhaustive list). These tend to work best when applied at the highest labeled rates, and either at the same time (if the label allows), or in close succession.

Be mindful of phytotoxicity, particularly on red soils on the east side of the Sacramento Valley, especially when applying the highest labeled rates. Not all these combinations will be effective in all fields or checks, depending on the watergrass species and biotypes present. Trying one of these combinations on a small amount of acreage, or different combinations on different fields, can be helpful to determine what will work best on your acreage.

Although not helpful for the current year, sending in watergrass samples for resistance testing to the University of California Weed Science Program can be an effective means to determine what products are working best on a particular field or check. Please reach out to your local Farm Advisor for assistance in collection.