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Multiple strategies for weed control

Most of the time when the subject of weed control in rice – or any crop for that matter – comes up, the first thoughts are of herbicides; what to use, rate, how much will it cost and so on. At a field demonstration recently, Dr. Eric Webster told producers the first step in good weed control is a good stand. As an agronomist, I agree 100 percent. In these days of technology, we often forget the lessons we learned about the value of good cultural practices in weed control.

At the recent Rice Technical Working Group meetings, Dr. Steve Linscombe, in discussing the changes in varietal development from the early 1900s to the present, referred to the introduction of semi-dwarf varieties. He pointed out that the tallness of early varieties was necessary because there were no herbicides. Weeds were controlled by deep water, and, to have deep water, you had to have tall varieties. That also accounts for the old figure of 3.5 acre-feet of water used to produce a rice crop in those days of deep flooding. Studies we have conducted in association with our verification fields show we now use from 20 to 25 acre-inches on the silt loam soils and 25 to 30 acre-inches on the clay soils.

It was, Dr. Linscombe said, the introduction of propanil herbicide that made possible the development of semi-dwarf varieties because we could control barnyardgrass without a deep flood, so we could grow shorter stature varieties. The introduction of semi-dwarf varieties dramatically increased yields because they could be fertilized more without the fear of excessive lodging that once limited how much nitrogen that could be applied to the tall varieties.

The development of chemicals that could selectively control weeds in a crop without damaging the crop was a huge step forward in agriculture. However, reliance on herbicides alone can set a trap for the farmer. Witness the problems we have begun to experience with out-crossing of Clearfield varieties to red rice and weed resistance problems to several herbicides and chemistries. This year I am hearing more growers talk about switching back to conventional varieties and water seeding to relieve pressure on current technology and possibly avoid some of the resistance problems others have encountered in the past few years. A wet spring is making that decision easier for some who might have planned to drill seed.

Dr. Webster pointed out several key ingredients to a good weed control program. I know you have heard them before, but repeating them sure cannot hurt. In addition to the good stand and good water management discussed in the preceding paragraphs, timely application of herbicides, proper herbicide rates and rotation of herbicide chemistries are key ingredients in any effective weed control program. The philosophy of waiting until all of the weeds have emerged so it only takes one trip over the field almost always results in unsatisfactory weed control and costs more than applying herbicides to young, actively growing weeds even if it means it might take two trips to do the job correctly. I cannot think of a single herbicide label that states, “Wait until all of the weeds are big and difficult to control before spraying.”

Following are a few specific comments from Dr. Webster about herbicide use in rice this year. His work with combinations of Newpath with propanil or propanil plus thiobencarb (Bolero, RiceBeaux) has shown an increased activity on red rice when compared to Newpath alone. He also said experience with the product Permit Plus indicates the rates should not be reduced because that will result in too low a rate of the active ingredient thifensuluron – the Plus part of the herbicide. League, another of the newer herbicides, Dr. Webster prefers in the postemergence application timing rather than preemergence. For a complete listing of all of the recommended herbicides for Louisiana, refer to the publication Rice Varieties and Management Tips 2012. It is available in hard copy through your local county agent or through the LSU AgCenter’s rice Web page at: lsuagcenter.com/en/crops_livestock/crops/rice/Publications/.


Barnyardgrass

The main culprit in weed resistance in rice is barnyardgrass. It has been one of the most troublesome and costly weeds in rice for years now. With a large genetically diverse population, barnyardgrass has an increased ability for resistance issues. Through extensive barnyardgrass resistancescreening programs in Mississippi and Arkansas, barnyardgrass resistance has been documented to propanil, Facet (quinclorac), Command (clomazone), and ALS herbicides (Newpath, Beyond, Regiment and Grasp). Therefore, it will be imperative to implement a weed resistance management plan before it becomes a more widespread problem.

A weed resistance management plan starts with rotation – crops and herbicides. With a possible reduction in rice acres again this year, it would be good time to manage weeds with different herbicide chemistries that are not available in rice. Good herbicides for residual barnyardgrass control and resistance management in soybean include Dual, Outlook and Warrant. These preemergence herbicides, along with glyphosate, will help tremendously in trying to prolong our existing herbicides in rice. Also, try to keep fields clean well past harvest. As combines roll through the field, barnyardgrass gets left behind and is allowed to produce viable seed that goes back into the soil. If this occurs, it is just adding more to the overall grass problem, which ultimately costs more money later, especially in rice.

Effective weed control in rice can still be achieved, even with the limited amount of herbicides available. To keep Clearfield rice and ALS herbicides an effective program for barnyardgrass control, other herbicide MOAs will need to be included in the overall program. Including other MOAs such as Command, Prowl, Facet or Bolero in a Clearfield system will be necessary. In conventional herbicide programs, preemergence herbicides such as the ones mentioned will need to be utilized as well. Apply a residual at planting and another at the early to mid-postemergence timing. As with all herbicide programs, timing is everything.

The best plans can be made, and Mother Nature has a way of disrupting them. Never be scared to spray early if given a good opportunity. You don’t get calls on spraying weeds too early, but the phone always rings about weeds sprayed too late.


Avoid resistance

As we approach the 2012 rice production season, growers need to be aware of the increasing problem of weed resistance that we are facing as a whole in the rice industry. We currently have documented many populations of barnyardgrass that are resistant to propanil and Facet herbicides. In addition, several populations have been found that are resistant to Newpath. A few of these populations are resistant to propanil, Facet and Newpath. These trends are starting to show up in other rice-producing states as well.

For many years now, we have relied on Command and Newpath as our backbone rice herbicides. In fact, at least two-thirds of the rice being grown in Arkansas is Clearfield rice. According to a recent survey, as much as 40 percent of this rice only receives Newpath for barnyardgrass control. In addition, at least 10 percent of Clearfield rice has not been rotated out of Clearfield rice since 2006. This is all a recipe for promoting the occurrence of ALS-resistant barnyardgrass and increasing the possibility of developing an ALS-resistant red rice, which would render the Clearfield system useless in terms of controlling red rice. It is more important now than ever that growers recognize the value of crop rotation to prevent the build-up of resistant grass species in rice.

Currently, there are no new herbicide modes of action being developed for rice, and the development of genetically modified rice has also been put on hold due to the lack of acceptance of GMO rice nationwide and worldwide. With all of this in mind, growers should be aware as they develop their rice weed control programs that the best approach for managing herbicide-resistant weeds is to develop a sound weed control program that incorporates at least two herbicide modes of action against barnyardgrass. Also, growers should be aware that the continuous use of Clearfield rice without soybean rotation in the program will eventually result in the development of ALS-resistant red rice.

In Arkansas, we have placed herbicide mode of action and the prevention of the further development of resistant barnyardgrass and red rice at the top of our priority list. For more information on herbicide mode of action and how you can develop a sound rice weed control program for your farm, please consult the Arkansas publication MP44, which can be found at your county office if you live in Arkansas. It’s also available on the Web at
www.uaex.edu
.


Rice Research Entomologist

I hope this year is not a repeat of last year – insect-wise and weather-wise. The drought in Texas is starting to ease, but we still need more rain to fill Lakes Travis and Buchanan, which are northwest of Austin and supply our farmers in Colorado, Wharton and Matagorda Counties with precious surface water. Anyway, I will address the water issue in more detail in a later article.

However, 2011 was a weird year for insect problems, mainly related to the drought. We experienced late rice water weevil problems, high stalk borer populations in certain areas, chinch bug damage in Liberty and Chambers Counties and high fall armyworm and rice stink bug populations on ratoon rice, which is very odd. As far as this year, we have some excellent insect management tools available. Three seed treatments – CruiserMaxx Rice, Dermacor X-100 and NipsIt INSIDE – have all given excellent results in our trials.

In Texas, NipsIt INSIDE has an Experimental Use Permit this year and can be applied to seed for planting on no more than 10,000 acres. If all goes as expected, NipsIt INSIDE will have a full federal label (Section 3) next year. Last year, in a hybrid seeding rate experiment, my project found that all three seed treatments performed very well against the rice water weevil; in fact, the average yield increase compared to the untreated for all seed treatments was more than 1,100 lb/acre. My project’s results consistently show an economic return on investment for all three seed treatments.

CruiserMaxx Rice and NipsIt INSIDE control a similar spectrum of insects including rice water weevil, chinch bug, thrips, aphids and grape colaspis, while Dermacor X-100 controls rice water weevil, fall armyworm and stalk borers. CruiserMaxx Rice also has three fungicides to control seedling diseases.

In multiple experiments over the past several years, my project has found Dermacor X-100 not only controls stalk borers on the main crop but also on the ratoon crop. In Texas, Dermacor X-100 recently received a 2(ee) label for use of a reduced rate for hybrid plantings (20-30 lb/acre seeding rate). The 2(ee) allows a rate of 4-5 fl oz/cwt seed instead of 6 fl oz/cwt seed.

In addition to the seed treatments, Texas farmers may be able to use Tenchu 20SG against the rice stink bug and grasshoppers in 2012. Texas rice farmers were able to use Tenchu 20SG last year under a Section 18 Emergency Exemption. We applied for another Section 18 for this year and expect approval before the use season, which typically begins the first of June.

If you want to access the 2012 Texas Rice Production Guidelines, please go to this link: http://beaumont.tamu.edu/eLibrary/ExtensionBulletins_default.htm. If you want access to my project’s annual report of research for 2011, go to the following link: http://beaumont.tamu.edu/eLibrary/Reports_default.htm?lastname=WayAnnualReport11.

I want to thank all the good folks in Arkansas for hosting the 34th Rice Technical Working Group Meeting (RTWG) in Hot Springs. I’m writing this article during the meeting between sessions. It’s been a very productive meeting for me. I’ve made some good contacts for future research and have enjoyed visiting with my university and USDA colleagues, industry cooperators and farmers. This meeting is held in even-numbered years. The next meeting will be in 2014 in the great state of Louisiana. I encourage you to attend the RTWG – the premiere rice research and Extension meeting in the United States.

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