Friday, April 12, 2024

Specialist Speaking

ss-wayDr. M.O. “MO” Way
Rice Research Entomologist

Control 6-legged pests

When I discuss topics other than insects, I get a little nervous, but, finally, this month, I get to talk about six-legged critters! For starters, let me emphasize the importance of scouting and explicitly following pesticide label instructions. If you do not hire a crop consultant, you must inspect your rice carefully and frequently to make effective, affordable and safe pest management decisions. If you can’t identify an insect or you want more information about a particular insect, contact your local rice scientist or contact me at (409) 658-2186 or In Texas, we have a complex of insect pests that attack rice from planting to maturity. The Insect Management section of the 2014 Texas Rice Production Guidelines describes these pests/damage and provides control options. The website link is: Guidelines.pdf.

However, I want to make you aware of a relatively new pest management tool (not listed/described in the above bulletin) now available for Southern rice farmers. Fastac EC is a pyrethroid insecticide containing the active ingredient alpha-cypermethrin. Like other pyrethroids, Fastac EC has broad-spectrum activity to control pests with chewing and piercing-sucking mouthparts. Thus, the label includes aphids, chinch bug, fall armyworm, grasshoppers, rice water weevil and rice stink bug. Some Texas rice farmers tankmix a pyrethroid with their preflood herbicide to control rice water weevil. This is a very effective and economical practice. We have found pyrethroids give excellent control of rice water weevil when applied close to the flood – preferably just prior to flood.

Rice water weevil is our numero uno rice pest across the U.S. The treatment threshold for this pest is very low – about three larvae per core (4-inch diameter by 4-inch deep plug of mud containing rice plants). I can walk into virtually any untreated rice field two to three weeks after flood in Texas and find rice water weevils. This is why insecticidal seed treatments can be a good option for control. My project’s research consistently shows significant yield increases when this root-feeding insect is managed. We also have data to show that when this critter is controlled in the main crop, increased yields are produced in both main and ratoon crops. Sometimes, the yield increase is greater in the ratoon compared to the main crop. You can access my project’s 2014 Entomology Research Report via the following link: This report describes all my project’s experiments conducted in 2014. From these reports, you can readily see the excellent benefits of controlling rice water weevil, as well as other pests.

Speaking of other pests, this year my project involves revising treatment thresholds for rice stink bug. Instead of employing cages, we plan to work in growers’ fields. We want farmers to optimize insecticide applications to “get the most bang for the buck.” Don’t overuse and don’t underuse, which means insecticide applications must be based on scouting, field history and other agronomic factors.

ss-atwellSam Atwell
Agronomy Specialist

Maintain field surface

High-yielding, high-quality rice production revolves around good water management. An abundant supply of good quality irrigation water is needed for optimum rice production, and the Missouri Bootheel is blessed with an abundant supply of good, clean water. Thirty acre-inches of irrigation water pumped per year is average for Missouri rice fields. Although our water supply is very good, close to the surface and relatively inexpensive to lift, it does cost money and fuel to do so. Most Missouri rice fields are precisiongraded. Our rice is normally flooded at the fifth leaf or first tiller and a two- to four-inch flood is held the entire season.

Prepare your fields now for uniform shallow floods: Yearly preplant field leveling or smoothing is essential for seedbed preparation, surface drainage and maintaining optimum flood depths. A landplane or float should be used to remove reverse grades, fill “potholes” and smooth out old levees, rows or ruts in a field. Rice can germinate under either soil or water, but not both. Therefore, maintaining a field surface that provides good drainage is important for stand establishment; controlling weeds, diseases and insects; maintaining desired flood depths; and providing a dry field for harvesting.

A water supply is adequate for a given field if you can flush in two to four days, flood in three to five days and maintain uniform flood for the entire season.

It’s rare, but we can have isolated water quality and quantity problems in our Missouri rice fields. However, it is common for old and not-so-old irrigation wells to be performing poorly, which could leave the appearance of an aquifer water supply problem rather than a clogged well. Knowledge of the quality and quantity of irrigation water is required for proper water management and high-quality, high-yielding rice. My water quantity information comes from the Missouri State Geologists with the Missouri Dept. of Ag at Jefferson City. They list nine wells across southeast Missouri (SEMO) counties with real-time monitors that allow you to see the aquifer water levels any time. We irrigate about 85 percent of the alluvial plain farm land in SEMO and about 95 percent is pumped from the ground.

Correct diagnosis of problems concerning irrigation water quality and quantity is critical for effective management. Water quality testing is an important step in diagnosing existing problems and identifying potential problems. Samples can be taken and tested at the University of Missouri Soils Lab at The University of Missouri Delta Center at Portageville. Several values are helpful in evaluating the quality of a particular water source. These include calcium concentration, bicarbonate concentration, chloride concentration, electrical conductivity (EC) and sodium absorption ratio (SAR). These can be found in (Table 9-7) in the UAR Rice Production Handbook. Also, iron and magnesium can be a problem.

For further information on taking a well sample, call Dr. David Dunn, University of Missouri Soil Lab, at (573) 379-5431, or Sam Atwell, Agronomy Specialist, at (573) 429-9141.


Dr. Jason Bond
Weed Science Specialist

Unique Challenges

As the weather attempts to warm up and fields are starting to dry up, rice planting will begin fairly soon. At this point, varieties have been chosen and seed treatment decisions have been made. Planting date has been shown to impact rice yield, with rice early planting dates generally producing the greatest yields.

The earliest planted rice also faces some unique challenges. The greatest challenge is establishing an acceptable stand, especially when rice is planted at reduced seeding rates. In early planting situations, an insecticidal seed treatment is very important. Dr. Jeff Gore’s program has evaluated multiple seed treatments for use in rice, and his data suggests the following.

Insecticidal seed treatments, such as Cruiser or NipsIt INSIDE, provide good control of early season insect pests in rice that can influence stand establishment. Chinch bug is one insect pest that can be devastating during the seedling stage, especially in fields adjacent to turnrows and fallow areas with dense infestations of Italian ryegrass. Chinch bugs are only an occasional pest, but they can cause severe problems in fields where they occur. Both Cruiser and NipsIt INSIDE provide good control of this pest.

We must also keep in mind that seed treatments face unique challenges on the earliest planted rice. The clock starts ticking on how well a seed treatment will perform as soon as the seed is put in the ground. The earliest planted rice generally takes longer to emerge with seedling growth usually progressing slower early in the season because of cooler temperatures. For the most part, both of the seed treatments mentioned above will perform better for rice water weevil control if the permanent flood is established four to five weeks after planting compared to six to eight weeks after planting. When seedling emergence and growth are delayed, rice water weevil control from these seed treatments will not be optimized.

Rainfall is another factor that can impact the performance of insecticide seed treatments. If we experience a weather pattern like we have observed in the last couple of weeks and receive heavy rainfall over an extended period of time, the performance of these seed treatments for rice water weevil control will be reduced.

Dermacor is an additional seed treatment that is labeled in rice. Dermacor is a different class of chemistry that provides longer residual control under adverse conditions. Dermacor will usually provide good control of rice water weevil even when seedling growth is slow and heavy rainfall occurs. The downfall is that Dermacor provides little, if any, control of other early season pests that can reduce stand.

In conclusion, insecticide seed treatments are an important tool to establish optimum plant density and get the crop off to a good start. Use of a seed treatment to help alleviate multiple stresses on early season rice generally will pay off in the long run.

DustinHarrellDr. Justin Harrell
Extension Rice Specialist

Water Management

The ability of a rice producer to effectively manage water is one of the most important keys to a successful rice crop. Early in the season, we must monitor soil moisture to determine the optimum time to drill-seed rice. The field must be firm enough to hold the farm equipment, have adequate soil moisture to germinate the seed, but it also must be dry enough to allow for the drill row to be closed with the press wheels.

This year in southwest Louisiana, early March rainfall events delayed drill-planting. The mid-March rainfall events that were forecast did hit much of the Texas, Arkansas and Mississippi rice production areas. These events delayed planting in those areas but somehow dissipated over southwest Louisiana as it tracked north and west. Only sporadic events hit the area and an estimated 40 percent of the rice acreage was able to be planted from March 22-28. The following week allowed for even more acres to be planted, and the season seems to be off to a great start in Louisiana so far.

Once the rice is in the ground, we need to determine if and when we need to flush irrigate the rice. In order for this to happen, the producer must make sure that his levees are pulled. Depending on his situation, this can be done before or soon after planting. The first flush could be triggered due to lack of soil moisture needed to germinate the rice to produce an even stand. Or, it could be triggered due to the necessity to activate a herbicide. Ideally, we would like to be able to flush a rice field in two to four days.

Sometimes, in order to save a flush, producers often watch the weather reports and, if a significant rainfall event is predicted, he may wait for the rainfall event. If the rain does not come as predicted, the flush event will be triggered the next day. This can sometimes be a gamble and could lead to uneven stands of rice and poor control of weeds.

Once it is time to establish the permanent flood, it is ideal to have the pumping capacity to establish the flood in three to five days. However, many fields may take twice this long to establish the flood. One of the things that makes establishing the flood in a timely manner is nitrogen (N) fertilizer management. Typically, we would like to apply N fertilizer as urea or ammonium sulfate on dry ground and incorporate the N with the flood. The flood water stabilizes the ammonium form of N. If a flood takes more than three to four days to be established, gaseous losses from ammonia volatilization can occur. In this situation we recommend treating the urea with a urease inhibitor that contains the active ingredient NBPT. This will temporarily stabilize the N and reduce volatilization losses.

After the initial flood is established, water management decisions are continually made on a daily basis – when to start and stop irrigation to maintain the flood and whether to drain the field because of zinc deficiency, straighthead management or even rice water weevil control in a situation where an insecticide seed treatment was not used. Once the call has been made to drain a field during midseason, this usually causes a domino effect where other management decisions have to be made. Like how dry should I let it get? How much N fertilizer should I apply when I re-establish the flood? How will this affect weed control? All are valid concerns when management decisions mandate releasing a flood.

Poor water management during the season can also lead to other problems during the season. The disease Blast is a prime example. If a field is allowed to dry, this often leads to a higher infection rate of the fungus. This is why we often see this disease show up first along the edges of fields an on high spots in the field.

One of the final water management decisions we make every year is when to drain for harvest. Hopefully, you will have an even stand of rice of similar maturity to make this decision! Typically, we recommend draining when one-half of the rice panicle is straw-colored on a silt loam soil and when one-third of the panicle is straw colored on a clay soil.

Once the rice is harvested, water management decisions are still not complete here in Louisiana and Texas. The next decision is whether to flush or immediately establish the flood for the ratoon crop, but we will save that discussion for another time.

Dr. Luis Espino
Rice Farming Systems Advisor

Arthropod Management

We are lucky that in California we don’t have as many insect pests as in other parts of the country or the world. Rice seed midge, rice water weevil and tadpole shrimp (not an insect but a crustacean) can infest rice early after planting. Later on, armyworms may infest rice fields mid-season. Following are a few updates on arthropod management in California rice.

The rice water weevil infests fields soon after flooding. Larvae feed on the roots and cause symptoms similar to N deficiency. Usually, infestations are limited to the first 20 to 30 feet next to field borders or levees, and this is where damage occurs. Recent research indicates that the variety M- 206, planted in roughly half the acreage, is more tolerant to rice water weevil injury than older varieties, even though weevils tend to prefer it. This may explain why the relative importance of rice water weevil as a pest has decreased. At the same time, M-202, an older, more susceptible variety, is on its way out; it is only planted in 10 percent of acreage. Another recent research find indicates that seeding rate does not have an effect on weevil infestation or damage, meaning that in areas where weevil is a problem, increasing the seeding rate will not reduce infestations or compensate for weevil injury.

Tadpole shrimp seems to be a re-emerging pest in rice. This was an important pest during the 1980s. Back then, organophosphate insecticides were used intensively to control several pests in rice, including tadpole shrimp, and, as a result, tadpole shrimp developed resistance. Currently, tadpole shrimp management relies on pyrethroid insecticides. The acreage treated with pyrethroids has increased from 11 percent in 2005 to more than 30 percent in 2013. Although some of these applications are also directed at rice water weevil, the increase is most likely due to tadpole shrimp. The use of a single insecticide mode of action against this pest raises the risk of resistance development, as experienced before. Recently, a suspect pyrethroid resistant population had been causing problems for several years in one field in Colusa County; fortunately, this population was confirmed as not resistant last year.

In the past decade or so, there have been several instances in which growers reported their grain quality being reduced from Grade 1 to Grade 2 because of an increase in proportion of damaged kernels. Lodged rice or early fall rains, common causes of damaged kernels, were not the issue. Larry Godfrey, UC Davis Extension Entomologist, and I conducted a survey of one of these fields to determine if an insect may be causing the problem. We found a redshouldered stink bug. I had collected this stink bug from rice fields in Colusa and Yolo counties in the past, but thought they were just “visiting.”

After a valley-wide search, we found this stink bug at low densities in several fields, especially weedy ones. In going through some historical documents, I found a handout in my office from 1965 that referred to an outbreak of this stink bug injuring rice kernels in 1939. We have conducted experiments in which we caged redshouldered stink bugs in rice plants and found that their feeding can damage kernels causing “peck,” a discoloration of the kernel. Pecky kernels are considered damaged kernels, and, therefore, can cause the reduction of the grade. Pecky grains also are more prone to break during milling and can result in lower head rice yield.

We are asking producers and pest control advisers to be aware of this insect and report any finds in rice fields (635-6234 or We’re not sure if the redshouldered stink bug is the cause of downgraded rice, but we will continue to investigate.

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