Weed Control

ss-hardkeClean Early, Clean Late

Rice Extension Agronomist
University of Arkansas,
Cooperative Extension Service

Good season-long weed control begins with good early season weed control. A good burndown application or tillage practice prior to planting sets the tone for the year. As we begin to get rice in the ground and it’s time for pre-emergence herbicides, it’s all about activation, activation, activation. We try to emphasize the importance of “finishing the field” at planting. Once the rice is in the ground, we need to get the levees up and the gates in so we can flush if we don’t get a rain to fully activate our residual herbicides. I know flushing isn’t that popular, but it should be less popular to waste an herbicide application and put money down the drain.

Unfortunately, some fields just aren’t set up to be able to flush. The answer for those fields is probably to do the best we can to get that field to a flood as fast as possible. If we can’t get the residual activated, the answer may be to focus on contact herbicides. Maybe apply some ammonium sulfate to get the crop growing faster so we can get to flood. Just don’t expect a yield bump from that ammonium sulfate application. It won’t be there, but it can help us get the crop where we need it to be. Favorable weather and use of multiple herbicide modes of action are ultimately the keys to good weed management. We can get it done if we stay after them.

Keep in mind that there is no such thing as a “salvage” treatment – it’s nothing more than a “revenge” treatment. Once weeds are large they have already done most of their damage and we don’t usually get enough efficacy to prevent them from going to seed. Spend money wisely to get them while they’re small; don’t use up your budget with a revenge application.

ss-atwellTechnology & MOA

Agronomy Specialist

At our annual Missouri Rice Producers Conference recently, we addressed topics on weeds, diseases, insects, fertility and marketing. Our producers are telling us that Missouri rice acres will be up in 2014. And they are focusing on a good early start for the 2014 season. Their attention is on selection of varieties, early control of resistant and other weeds along with early insect and disease control in rice.

ss-atwell-larve-01We confirmed the value of early and frequent flushing in dry springs for herbicide activation, which resulted in good early season weed control. During dry periods, we are forced to flush early and often for rice seed germination. With conventional and Clearfield rice, we recommend starting clean with tillage or a burndown, followed with a pre/delayed pre, early post herbicide program.

We estimate that Missouri growers plant about 50 percent Clearfield technology. We suggest matching these technologies and mode of action to your specific weed problems. And, we must pay attention and plan now not only for what your neighbor is planting in the field next to yours but to all applicators in the area throughout the season. My work on drift and misapplications shows me how complicated it is. That’s why I’m emphasizing to all producers to plan carefully and fully now. Also, it’s a good idea to mark your fields with the standard color coded flags for conventional, Clearfield, glyphosate and LibertyLink technology.

For early insect control, we are following the insecticide and fungicide seed treatment recommendations of the University of Arkansas’ Dr. Gus Lorenz. Due to the low seeding rates and cost of seed, it’s very important to control seedling diseases and insects. And, the best way to get seedlings off to a healthy start is seed treatments that are matched to your insect and disease situation. Missouri producers ended the 2013 season with a good yielding rice crop. The quality was good, and our pumping cost was low. But, 2014 is another year, and everyone knows it will not be like the past two.

We suggest identifying specific problems for each field, studying options for solutions and building a plan to match the technology to get positive results. In addition, we recommend hiring a consultant, along with your retailer and University of Missouri personnel, to help you.

I know it’s not simple. That’s why God made a farmer.

Don’t forget about herbicide plant-back interval (PBI) restrictions for rice. A few examples: 2,4-D – 21 day PBI; Beyond – 9 months; Newpath, Clearpath – 18 months; Flexstar, Prefix, Reflex – 10 months; Dicamba – 15 days; and Clarity – 21 days. There are others! Think about what you sprayed on last year’s crop in that field and then plan accordingly.

Treat the seed! That’s the answer for early season insect control. CruiserMaxx Rice, NipsIt INSIDE and Dermacor X-100 are our currently available insecticide seed treatments. While the greatest return on the use of these products is usually seen when early season conditions are difficult, the benefits are still there under better conditions. Trying to decide which of the three to use? CruiserMaxx contains an insecticide and fungicides. NipsIt and Dermacor are both insecticides only. Choose the one that you can get for the best price, but make sure you’re comparing apples and apples – price them based on insecticide plus fungicide seed treatments, which have to be added in for NipsIt and Dermacor.

CruiserMaxx and NipsIt provide good control of grape colaspis and rice water weevil as well as other early season pests (e.g. aphids, chinch bugs). Dermacor is a little better against rice water weevil but not quite as good against grape colaspis, and don’t expect the control of those other pests. In Arkansas, Dermacor is labeled for use in water-seeded rice, where rice water weevil is worst and grape colaspis is less of a concern (CruiserMaxx and NipsIt cannot be used in water-seeded rice).

Recipe for early season success: use burndown and residual herbicides (activate!), flush if needed, use multiple herbicide modes of action, and use insecticide and fungicide seed treatments.

ss-saichukHerbicide Chemistry


Writing about weed control issues in rice is a lot more interesting than writing about it in other crops where the article is about glyphosate resistance. This is what can be expected when one herbicide chemistry so dominates the market that the others slowly disappear leaving us open to exactly what has happened. Yes, we do have herbicide-resistant weeds in Louisiana rice, but the cases are more localized and involve more than one herbicide chemistry.

The issue of herbicide chemistry has become so prominent that the industry has developed a system of classifying herbicides according to their mode of action. For example, Group 1 includes the ACCase inhibitors. These herbicides affect acetyl CoA carboxylase. Group 2 includes the ALS herbicides, which affect acetolactate synthase. Now you know why even scientists use the abbreviations. Group 9 includes glyphosate. The idea is to try to avoid the use of herbicides within the same group number or mode of action to try to curtail the development of herbicide resistance.

Clearfield rice varieties are tolerant to the ALS herbicides Newpath and Beyond and mixtures containing their active ingredients. There should be a large No. 2 on containers of these herbicides. Most of our ALS resistance in rice surrounds either outcrosses of Clearfield varieties to red rice or volunteers and segregates from Clearfield hybrids and their progeny. Since the introduction of Clearfield technology, stewardship has been as much a part of the program as herbicide rates and timing. Farmers who have practiced good stewardship are still using the technology like they did when it was first released. Others who adopted the attitude that they would use the technology until they could not because they were confident something else would come along are now forced to revert to water seeding to suppress red rice on their farms.

The good news is that their wish will come true. The bad news is that it will be a few years before the technology is available. BASF recently announced the introduction of Provisia rice. Through mutation breeding, THIS IS NOT A GMO. They discovered a single mutation gene that provides resistance to ACCase inhibitor herbicides. The active ingredient in the herbicide to be used with the system is quizalofop-p-ethyl. These herbicides are often called “Fops,” which is much easier to say and spell. They are in Group 1. If you have a good chemistry background, you may recognize that the active ingredient is the active ingredient in Assure II herbicide. Prior to Roundup Ready soybeans, a number of grass herbicides or graminicides were on the market. Poast, Fusilade, Select and Assure were the front runners in this group. You may also remember that these herbicides only controlled grasses – not broadleaf weeds and not sedges – only grasses. Their other peculiarity was that they could not be tank mixed with many of the broadleaf herbicides because the broadleaf herbicides antagonized the grass herbicides making them ineffective. It made for a hectic herbicide application schedule. If grasses were large, we used the graminicide first then waited a week and applied the broadleaf controlling material. If the broadleaf weeds were the primary target, we reversed the sequence and could apply the grass material a little closer to the broadleaf material application. It was a mess.

Unlike Newpath, this herbicide will not provide any residual control, will not control broadleaf weeds and will not have any impact on sedges. It is an excellent red rice material. It will be a little more difficult to use than Newpath, but it may help save the Clearfield technology. In some crops, genes for resistance to two or more herbicides have been incorporated into the same variety. Often, this is referred to as “stacked gene” technology. This new rice herbicide tolerance gene will NOT be stacked onto Newpath resistant genes.

We will always deal with the potential for outcrossing in rice. Stacking the genes would be very unwise because when outcrossing occurs, the outcross plant will be resistant to both technologies. By keeping the genes separate, growers will be able to switch between technologies using Assure to control undesirable weedy rice forms resistant to Newpath and control weedy rice forms resistant to Assure with Newpath. I referred to Assure here, but I am not sure if the herbicide label will use that name or a new name to keep it separate. A new non-GMO technology is truly good news even if it is a few years away.

ss-wayCorrectly Identify Insect Pests

Rice Research Entomologist

This month’s topic is insect management, which is right up my alley. I remember back in the early 1990s we only had 3G Furadan to control the rice water weevil in Texas; now we have three seed treatments, an insect growth regulator and six foliar applied insecticides! All of these tools provide excellent control of this root-feeding pest when applied at the proper rates and times. We recently published the 2014 Texas Rice Production Guidelines, which you can access via the following link: https://beaumont.tamu.edu/-eLibrary/Bulletins/ 2014_Rice_Production_Guidelines.pdf. In the Insect Management Section, you can obtain more information on the proper use of the above insecticides.

ss-way-nymphs-01I do want to mention we left out Fastac in our Guidelines because of time constraints in trying to get this bulletin to you. I apologize for this omission. The active ingredient in Fastac is alpha-cypermethrin, which is a pyrethroid insecticide. Go to this link to read more about Fastac  http://pdf.tirmsdev.com/Web/17/82421/17_82421_LABEL_ English_.pdf?download=true.

We entomologists argue about seed treatments and Integrated Pest Management (IPM). Some of my colleagues believe seed treatments are not part of IPM because seed treatments are preventive – you must apply them before you know what pests and densities you will eventually have. These folks believe pesticides must only be applied after scouting fields and determining pest population levels. If populations exceed the treatment threshold, then spray.

Personally, I do not agree with this viewpoint. First, the vast majority of rice fields in Texas, if left untreated, will produce above thresholds of rice water weevil larvae (the treatment threshold is only three larvae per 4-inch diameter core). Second, seeding rates are low (e. g. hybrids), which means you must protect your investment (seed costs have dramatically increased). Third, seed treatments do not have an application cost. Fourth, seed treatments minimize or eliminate drift of pesticide. Fifth, seed treatments reduce management costs associated with scouting fields. Sixth, seed treatments provide “peace of mind’ for farmers. Thus, I believe seed treatments are a valid component of IPM – they are cost effective.

I know we will be planting very soon, so scout your fields for pest infestations from emergence onwards. Early seedling pests in Texas are chinch bug, aphids, thrips, leafhoppers and fall armyworm. Specific seed treatments and foliar-applied insecticides are labeled for these pests. If you scout your fields regularly and carefully, you will be able to detect these pest infestations before significant damage has occurred.

If you are not sure of the identity of a pest, contact your local rice CEA or research scientist. I remember a few years ago a rice farmer called me to inspect a “stale seedbed” field for what he thought were chinch bugs. This part of the Texas Rice Belt has a history of severe chinch bug damage to young seedling rice. The farmer reported that infestations were really high – the ground was literally crawling with these insects. Well, the farmer was right – under the dead vegetation from the stale seedbed technique was a virtual swarm of these “chinch bugs.” They looked like chinch bugs but were actually false chinch bugs, which feed primarily on decaying vegetation – not on seedling rice.

So, the moral of the story: inspect your fields for insects and get the correct identification. It may save you a spraying!

ss-linquistTadpole Shrimp

UCCE Rice Specialist

It seems in recent years the tadpole shrimp has become more widespread and abundant in California rice fields. Fortunately, it is not difficult to manage this pest with current registered treatments. However, tadpole shrimp develop fast. Eggs hatch two days after flood, and adults start laying eggs seven to 10 days after flood. Sometimes, they can go undetected before damage occurs.

The tadpole shrimp lays its eggs in the soil. These eggs are very hardy and can stay in the soil for years until the right conditions for hatching are present. They need a period of desiccation before they can hatch. This explains why we see more severe tadpole shrimp infestations in years with dry springs. As the soil profile dries out, more eggs get primed for hatching. Tillage brings these eggs to the soil surface, and as soon as fields are flooded, they hatch. Another factor that may play here is that fields may take longer to flood after a dry spring, giving tadpole shrimp more time to grow before seeding.

You can also notice the effect of desiccation in fields that are drained during the season. In a continuously flooded field, once you control the tadpole shrimp, they disappear. Eggs that were laid before control do not hatch because they have not gone through desiccation. However, if you control tadpole shrimp and later drain the field (for example, for a herbicide application) so that the soil surface cracks, you will probably see another tadpole shrimp infestation after you reflood. At this point, rice seedlings are large and will not be affected by the tadpole shrimp, but they will leave eggs in the soil.

Most applications for control of early pests in California rice are limited to borders and levees (and sometimes middle strips). This is based on the fact that the rice water weevil infests only borders and levees. However, tadpole shrimp don’t appear to follow this pattern. Last year I sampled two large fields from flooding to propanil timing and noticed that tadpole shrimp were present across the field in similar numbers. Border and levee treatments seem to do a good job of controlling the tadpole shrimp across the field.

All the conditions that favor good rice seedling growth and development also favor tadpole shrimp. This makes managing tadpole shrimp with non-chemical methods very difficult. Following recommended IPM practices such as reducing the time from flood to seeding, using vigorous seed and monitoring is the best way to ensure damage doesn’t occur. A potential way to reduce the egg bank in the soil is to time treatments so that they happen before eggs are laid. However, this may be challenging because of the eggs small size and the variability in tadpole shrimp growth rate due to temperature. I’m currently looking at the possibility of using degree days to predict when most eggs will be laid. If this approach works, it can be combined with the previously mentioned IPM tactics to reduce the buildup of eggs in the soil over time.

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