Rice Farming

 - Specialists Speaking -


Section 18 targets rice water weevil larvae

DR. M.O. “Mo” WAY
Rice Extension Entomologist

The topic for March is weed management, but first I want to talk about some recent regulatory actions pertinent to this year’s crop. All of the southern rice-producing states submitted Section 18s for Dermacor X-100, which is a rice seed treatment for rice water weevil larvae control. The active ingredient in Dermacor X-100 is rynaxypyr or chlorantraniliprole. This new class of insecticide is called an anthranilic diamide and causes rapid cessation of target insect feeding and muscle paralysis leading to death.

Dermacor X-100 has a very good environmental profile, which state and federal regulatory agencies view favorably. At the time of preparing this article, Section 18s were approved for Texas and Louisiana. Our Texas data from the past three years are very positive – Dermacor X-100 at the labeled rates provided excellent control of rice water weevil larvae.

I am very pleased that this product is available to Texas rice farmers in 2008. Dermacor X-100 is a DuPont product. Dupont is aggressively seeking a full federal Section 3 label for Dermacor X-100. Only authorized seed dealers can treat seed with Dermacor X-100.

I want to thank Ed Gage, pesticide registration specialist with the Texas Department of Agriculture, for all his hard work preparing the Section 18 package for Texas. I also appreciate the support of DuPont scientists Drs. Eric Castner and Charlie Grymes. This is a good example of how universities, agrichemical companies and governmental regulatory agencies can work together to benefit both the farmers and the environment.

Now back to weed management. Drs. Garry McCauley and Mike Chandler are Texas’ rice weed scientists, so specific questions should be directed to them. Also, refer to the 2008 Texas Rice Production Guidelines for detailed information on current weed management recommendations.

You can access this publication on the Beaumont Center Web site at http://beaumont.tamu.edu.

In addition, the LSU Agcenter has just published a very helpful rice weed identification guide in the form of a laminated fold-out that is very convenient for field use. Weeds are identified using a modified key with excellent pictures of seedling and mature weeds. The authors of this useful publication are Dr. Eric Webster, LSU weed scientist; S. Bottoms; J. Hensley; Dr. Ron Levy, county Extension agent; and Bruce Schultz.
You can obtain this great tool from Dr. Johnny Saichuk, Eric or Ron. As you probably know, Johnny is the LSU Extension rice specialist. A nominal fee will be charged for the publication. I already ordered 500 copies for the Texas AgriLife Research and Extension Center at Beaumont, which is the new, official name of our center.

The first step in weed management is correct identification of your target weeds, so the above publication is important. Carry a 16x hand lens and a sharp pocket knife to assist in identifying weeds. Also, carry some plastic bags or a small bucket in which you can place unknown weeds for later expert identification. A little water in the bags or bucket will keep the weeds fresh. Be sure to get all parts of the weed, especially the flowers or seeds.

Make sure you walk your fields often and thoroughly to know your weed situation. Also, not all of your fields are going to have the same composition and abundance of weeds, meaning you must check all of your fields.

Although I am a bug scientist, I do know from my experience that early control of weed problems usually is crucial to a successful weed control program. In general, the longer you wait to control certain weeds, the bigger they are and the harder they are to control. Your weed control bill can skyrocket quickly if you don’t control your weeds in a timely manner.

As far as weed management, I think poor timing of herbicide applications is the biggest problem I have observed. During the planting season, small, easy-to-control weeds can become large, hard-to-control weeds in just a few days. Again, this points to the importance of scouting and timing.

Lastly, I want to thank the California rice folks for putting on a great Rice Technical Working Group meeting in San Diego in February. Lots of good information was shared to help rice farmers make a living and feed a hungry world.

Timing & moisture

Dr. Nathan Buehring

To maximize yields and returns in 2008, early season weed control will be necessary. Two things that make early season weed control successful are timing and soil moisture.

Grass that has two leaves is a whole lot easier to control than grass that has five leaves. Research has proven this time and again. Therefore, to achieve the most effective control of grasses, it will be imperative to make the herbicide application in a timely manner. Once the grass gets big, you will never catch up and get a good handle on it.

On these clay soils, on which we grow a majority of our rice in Mississippi, a two-shot herbicide program will generally be required. I would add something in the tank that has residual grass control each time an application is made if you are not going to flood up immediately. Don’t hesitate in making that second application by just saying, “We will get it in the flood,” especially if there is a high population of grasses present.

Soil moisture is a key component in making herbicides work. For preemergence herbicides, the soil moisture conditions after the application are the most critical. A preemergence herbicide needs to be activated by rainfall or flushing soon after an application. This will move the herbicide into the soil so that it can work. If the activation of the preemergence herbicide is delayed, weeds can germinate and emerge before the herbicide is activated, which will result in a failure.

For postemergence herbicides, the soil moisture conditions at the time of application are the most critical. If weeds are drought-stressed, they are harder to control due to less of the herbicide being taken up by the weeds since they are not actively growing. As a result, it may be better to flush before an application to get the most effective control if a rain is not in the eminent future.

Although we often face them, salvage situations are not always the result of poor management. In a salvage situation, a two-shot program may be necessary, especially under heavy grass pressure. Therefore, I generally try to start cleaning up grasses before the flood. This will allow for reduced competition between the grasses and rice at flooding. Also, if there is less grass at flooding, not as much costly nitrogen will be lost to grasses.

In the last couple of years, I had good results with Regiment plus their new recommended adjuvant system for large barnyardgrass control. RiceStar is another good option if multiple grass species are present. On the second shot, I will go with 15 fl oz/A of Clincher in the flood. Also, in a salvage situation, it is always best to use 10 gallons per acre (GPA) by air and 15 to 20 GPA by ground.

If needed, don’t be afraid to spray twice

Dr. John Saichuk

Last year, the issue of weed control in rice was overshadowed by the discovery of the adventitious presence of LL601 in conventional rice. The collective efforts of the rice industry have accomplished in one year what even the most optimistic among us thought would be next to impossible. It is a great example of what can be accomplished when everyone works toward the same goal.

We will still be a little short of seed on some of the Clearfield varieties, but, for the most part, growers will have adequate seed to plant. In Louisiana, we are expecting an increase in both hybrid acreage and Clearfield acreage from last year. For those producers who plant Clearfield varieties, weed control options are much simpler than those planting conventional varieties, especially if they are farming land with red rice problems.

At all of the grower meetings this past winter, Dr. Eric Webster stressed several key weed control strategies. Some of these are things we have been hammering on for years, and they have not changed. One of the most important concepts is to apply herbicides to small, actively growing weeds. This is an old story that warrants repeating because we still encounter growers who try to wait “until every weed emerges” so they only have to spray once. It never works. While they are waiting for weeds to come up, other weeds are becoming too large to be controlled.

Dr. Webster also pointed out the need to choose the best herbicide for the job. My personal philosophy is a step-wise process. First, I select what I think is the best herbicide for the job. Second, if there are two or more herbicides that will work equally well, I select the one where I get the best product support. Choosing the lowest cost herbicide is the last step.

Another caution listed by Dr. Webster is to be careful when using reduced rates of herbicides. I’ve said before that reduced rates work best when the weeds are small, conditions are perfect, and you are lucky. I’m not against reducing rates when I am confident we can control the weed in question, conditions are ideal and the herbicide is going to be applied immediately.

When over-the-top herbicides were introduced in soybeans many years ago, we learned quickly that many of the grass control materials and broadleaf control materials could not be mixed without a loss in control. We are experiencing similar antagonism problems with some of the rice herbicides we use today. I am reluctant to mix anything if the weed spectrum contains any difficult-to-control weeds.

I think nothing is saved by trying to spray only once if another application is required to come back to clean up a sloppy job. Two applications may be more economical than one if both work well.

The emphasis on reduced tillage over the past several years has been good in most instances. However, one of the consequences of reduced tillage is the encouragement of the development of perennial weeds.

Because these weeds usually are poor seed producers, and their seeds often have low viability, they survive by producing rhizomes or stolons or other modified plant parts from which new plants can originate. Tillage is especially effective in destroying these vegetative plant parts.

One of our most difficult-to-control weeds is Creeping Rivergrass (Echinochloa polystachya) also known as Habetz grass, perennial barnyardgrass and a host of unprintable names. In one area where Dr. Webster has been conducting research on a producer’s farm, the farmer took his advice and has used the combination of tillage and herbicides to slowly reduce the problem to the point that the area is no longer suitable for research.

There are a few label changes anticipated for 2008.

Grasp herbicide has added some broadleaf weeds. Strada, a herbicide similar to Permit with activity on broadleaf weeds and sedges will be more available this year. Dr. Webster is looking into the pre-emergent activity of Permit, but it is too soon to make a recommendation for its use in that manner. He is also taking a good look at a Valent numbered compound.

Something new for this year is a weed control publication by Dr. Webster and his group that has color plates of a number of weeds on one side and a key to their identification on the other side. This publication is available on line at: www.lsuagcenter.com/en/crops_livestock/crops/rice/Publications. It is also available in limited quantities through your county agent.

As herbicides become more specific in their control spectrum, it is important to know the weed you are trying to control. This is a simple, easy-to-use tool that should help in that regard.

Use residual first

Extension Weed Specialist

I did not learn rice weed control back when the program was propanil every Monday until it is clean, then flood. By the time I came along, most program weed control approaches in rice included some kind of residual component. These included: Bolero, Prowl and Facet for the most part. Today we have more options, and still have these, too.

I believe in starting off with a residual grass material first and foremost for most Arkansas fields. For the money, Command applied PRE provides the widest spectrum of grass control available in one product. However, it is primarily a grass herbicide at the rates used in rice. Know the rate for your soil type, typically 0.8 pt/A on a silt loam and 1.6 pt/A on heavy clay. Do not use Command on cut fields. Command will miss most broadleaf weeds, including hemp sesbania (coffee bean) and northern jointvetch (indigo). It will release sedges and smartweed, so be ready to come back for those in a Command program. If your field has a heavy infestation of these broadleaf weeds, then another option that includes some early broadleaf material might suit your field. This could be a tank mix with Facet or even Permit. (There is a possibility that Arkansas will get a 24C label for Permit applied PRE-plant and PRE in rice for 2008).

At our location near Lonoke, Ark., my primary weeds are barnyardgrass, broadleaf signalgrass, hemp sesbania, northern jointvetch and nutsedge. When we have a trial that we want to keep weed-free, my program is 0.5 lb of Facet + 1.0 lb of Prowl per acre applied as early delayed-PRE as possible, just after the rice swells. We typically will follow that with 1.0 oz/A of Permit for sedges and any escaped broadleaf weeds that we might have. This is a pretty good program. You can also tankmix Command with Facet, although this increases the cost.

Last year the price of Facet went down a bit, and there is now a generic formulation in the marketplace called Quinstar. If the price comes down anymore, I think there will be a large increase in Facet or Quinstar use as a PRE. Advantages to using Facet PRE include fewer problems with Facet-resistant barnyardgrass, broadleaf control (sesbania, jointvetch and others), and keeping fields weed-free rather than cleaning them up.

Like all residual programs, a disadvantage of using Facet PRE is that you must have rainfall or a flush for activation. If you cannot or will not flush, then it is hard for me to recommend that you start off with a residual herbicide. The difference is night and day. If you are in this situation, then you are probably better off to go with an early-POST tank mix of one of these residual products with propanil or RiceStar and take a different approach.

The Clearfield system with Newpath herbicide continues to stand out. These are really the only fields that are truly “clean” at harvest. Last year, the cheapest Facet you could find was in the pre-mix product ClearPath (Newpath + Facet). It is just plain hard to go wrong with one ClearPath and one Newpath application in Clearfield rice. We have tried PRE followed by POST, POST followed by POST and switched up the ClearPath and Newpath timings, and plots were clean either way. Some growers prefer to use Command up front PRE in Clearfield rice and then come back with Newpath. These fields look good too, and the Command lets you focus the Newpath on the proper timing for red rice. If you go with any PRE application in Clearfield rice, a flush is absolutely critical. If you cannot flush it in case of dry weather, then go with the sequential POST.

There are some weeds that current residual herbicides, with the exception of Newpath, just are not that good on, such as smartweed, nutsedges and ducksalad.

Herbicides & water


Weeds can be a rice grower’s nightmare. No wonder. They cause more yield losses than any other pest in California rice. Part of the problem has been weed resistance. California rice has the dubious distinction of having more herbicide-resistant weed species than any other crop in North America.

The good news is that in recent years, a number of new herbicides have been registered for use in rice. The bad news is that most of them are knowledge intensive when it comes to water management. The space in this column is not adequate to cover how water should be managed for each and every herbicide. The primary point here is that if farmers do not have the ability to move water around with some speed and precision, it will be almost impossible to get the highest performance out of any herbicide, and they are all too expensive to get anything less.

So let’s take a few examples. Abolish is a good example of why water management can be extremely important. Rice needs to be approximately at the two-leaf stage, and the grasses and sedges no more than two-leaf. So that’s about five to seven days after flooding. If it takes seven days to flood the field, your goose is already cooked. You will have weeds barely germinated where the water hit last, and weeds just right where the water hit first.

For foliar active herbicides that require contact with the weed, such as Clincher, the water must be off to get good coverage but back on the field as rapidly as possible to suppress subsequent weed germination And so it goes, with every herbicide. So it’s critical that water be managed properly.

Field leveling is important for complete flooding and for draining with no standing water. However, flooding time is often limited by the amount of available water or by the size of large fields. Consider breaking the field into smaller units with individual inlets and outlets. Each small unit of one or two checks can be treated as a small field when necessary, moving water in and out with speed.

The shorter the flooding time, the more uniform the weeds will be for treatment. The faster the drain, the more the field can be treated at exactly the right stage for best control. The faster the reflooding, the quicker new weed seed germination can be suppressed.residual component. These included: Bolero, Prowl and Facet for the most part. Today we have more options, and still have these, too.