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
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:
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.
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
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.