- Specialists Speaking -
KELLY V. TINDALL
In June 2007, a single specimen was brought to the Delta Research Center in Portageville for identification. The specimen was collected from a rice field near Bakerville. In late May 2008, I received a call about a 40-acre field, located near Catron, of water-seeded hybrid rice that had not emerged. The field was drained and hundreds of thousands of tadpole shrimp were in the remaining puddles. Not a single viable seed was found. The field had to be replanted.
Another call was received in June about a field north and west of Catron in Stoddard County that was infested with tadpole shrimp. At least 4,000 acres had tadpole shrimp present and of those infested, approximately 2,000 acres were economically impacted. Infestations also caused approximately 100 acres to be replanted.
Tadpole shrimp are pests in California. However, they have not been previously documented to occur in rice production systems outside California. Only water-seeded systems have problems with tadpole shrimp because eggs hatch once fields are flooded. Immatures initially are filter feeders until they are large enough to feed on plant material. The smaller the plant when tadpole shrimp begin to feed on rice, the more damage is likely to occur. However, once rice plants break the water, they can tolerate tadpole shrimp. Rice planted using drill-seeded and dry-seeded methods is large enough when fields are flooded. Therefore, tadpole shrimp are not pests in dry-seeded systems.
Hybrid varieties are planted at a lower seeding rate (30 lbs/A) than conventional varieties (100 lbs/A). Fields with hybrid varieties are more susceptible to damage. Plants are not more susceptible to tadpole shrimp damage, but the low seeding rate makes the losses more apparent than with a higher seeding rate. Losing 10 percent of a stand planted at 30 lbs/A is more detrimental than losing 10 percent of a stand planted at 100 lbs/A.
Once rice is no longer vulnerable, tadpole shrimp may be biological control agents for mosquitoes and weeds. Tadpole shrimp are predators of mosquitoes, and the damage they inflict on rice (eating and/or uprooting seedlings) can also occur to weed seedlings. We still do not know the extent of the distribution of tadpole shrimp in Missouri, but we are confident it will only be a problem for water-seeded systems. And, in fact, it may even be beneficial to farmers in drill-seeded systems and once plants have broken the surface in water-seeded systems.
Weed control timing
One of my predecessors said that growing rice is easy. You only have to do four things. “You gotta’ get a stand, you gotta’ control the grass, you gotta’ fertilize the crop and you gotta’ have water.” This all sounds easy, but timing is critical for each of these things. These key factors also require decisions that are made early in the season.
Early season decisions are critical to final yields and overall profit because they influence the crop for the entire season. This is no more evident than in weed management. Rule number one: Small grass is easier to kill than big grass. Rule number two: Flushing generally makes residual herbicides more effective. Rule number three: Post-flood herbicide applications are salvage applications. Rule number four: Resistance happens. While these “rules” are not new or earth-shattering, they still hold true. Timing is everything and often means the difference between $40-per-acre herbicide costs and $100-per-acre herbicide costs.
Newpath is a very effective grass herbicide, and most of the increase in Clearfield rice acres in Arkansas has resulted from excellent control and ease of use. However, Clearfield rice becomes even more effective when Command is applied to these fields pre-emergence than when Newpath is applied alone. Command provides grass control for a few weeks to allow red rice to emerge. With Command, the first Newpath application can be timed for the most effective red rice control (after it has emerged) rather than for the most effective grass control. This also adds a new mode of action and reduces the probability of developing Newpath-resistant barnyardgrass.
Now consider non-Clearfield rice acres. Timing is still critical. Command is by far the most widely used grass herbicide for early season grass control. However, Command must have moisture to be effective. If conditions are dry, and you are unwilling to flush, Command will not work. Now I have heard all of the excuses about flushing, and it is difficult to talk some guys into turning on the well. However, consider the cost of NOT flushing. Not getting effective grass control with Command means a good possibility of ending up with bigger grass than can be killed effectively.
An investment of $12 to 13/acre to flush sounds cheap compared to $25 to 40/acre for a salvage application. If the grass is not controlled prior to flooding, it will compete enough to reduce yields. Yield loss has already occurred if you are trying to control a large amount of grass after flooding.
Although not currently in the same population, resistance has been developed to most of the rice herbicides used for grass control in Arkansas. Resistant barnyardgrass has been found to propanil, Facet, Command and the ALS family (Newpath, Grasp, Regiment). Dr. Bob Scott and Dr. Jason Norsworthy have suggested that resistance to Ricestar HT and Clincher is likely to occur soon because of the nature of these herbicides.
When you look at this list, options are reduced to Prowl and Bolero (thiobencarb). Both of these products are much more effective pre-emerge, and the options for post-emergent control of grass are becoming precarious. Growers should not only use different herbicides, but also make sure different modes of action are used. Mixing Grasp or Regiment with Newpath does not provide any additional modes of action and will not reduce the probability of resistance development.
I realize that resistance to all of these herbicides is not present in the same field, but the fact that resistance is developing should increase growers’ awareness. We need to get effective control on small grass so that we are not as dependent on salvage operations to control grass. Use multiple modes of action and flush if necessary.
In 2009, there will be another increase in the amount of rice grown in a Clearfield cultivar. The Clearfield technology was first adopted for the control of red rice. Now, more acres are being planted into a Clearfield cultivar because of the simplicity of the weed control system and protection from Newpath drift.
Dr. Nathan Buehring
The immediate threat to the technology is barnyardgrass resistance to Newpath. There has already been one documented case of Newpath-resistant barnyardgrass in Arkansas. As this technology expands to more acres, I would expect resistance issues to expand to more acres.
Using herbicides with multiple modes of action will be one of the most effective ways to prevent or slow the progression of resistance. Adding pre-emergence herbicides such as Command, Prowl, Bolero and Facet (which all have different modes of action) into a weed control program will help prevent or slow the progression of Newpath-resistant barnyardgrass.
Crop rotation will be equally as important in resistance management. Soybeans need to be consistently grown behind Clearfield rice. Also, use multiple modes of action for weed control in soybeans. A good addition to glyphosate would be Dual or Outlook for pre-emergence control of grasses in soybeans.
It is highly important to consider resistance management because the herbicide development pipeline is essentially empty with no new developments. Therefore, the herbicides that we have today in rice could potentially be the same herbicides that we will have 10 years from now. Preserving herbicides and herbicide technologies will be key in being successful now and in the future.
Herbicides & water
Dr. John Saichuk
Back in the mid-1980s, about all we had to control weeds in over-the-top applications in soybeans were Blazer and Basagran. Most growers wanted to “wait for all of the weeds to come up, so they only had to spray once.” By that point, the drilled beans had closed the canopy, and weeds like morningglory and large grasses were growing under it; they eventually came through the canopy. I then told the farmers they needed to spray the field twice; once to defoliate the beans to expose the weeds and a second time to spray the weeds. They didn’t see the humor in it.
At producer meetings this winter, I emphasized that I cannot think of a single rice herbicide that does not perform better when used in association with proper water management. Allowing fields to dry after herbicide application is an invitation to poor herbicide performance. This problem has been most prevalent in Clearfield rice production. The success of this system has lulled farmers into believing they can save water, eliminate a rice water weevil control measure and prevent other disorders, such as localized decline and straighthead, by holding off permanent flood. That is a real misconception.
When we take on a new verification field, the first thing I ask the farmer is, “Do you have a history of sprangletop or fall Panicum?” Those two grasses (actually more than two because there are several species of sprangletop) have become more difficult to control as we transition from predominantly water-seeded, pinpoint flood management to water seeding and using a delayed flood or drill seeding. Also, producers have moved away from using propanil in overall weed management programs.
In drill-seeded rice, the best options to control sprangletop and fall Panicum have been either Prowl applied delayed pre-emergence or Command applied as a true pre-emergence. But in water-seeded rice, Command is the only pre-emergence tool in the box. Both work well if you follow the label guidelines and follow the herbicide application with water. Another option being revisited is the combination of propanil and Bolero early post-emergence.
Post-emergence options are also limited, especially on larger grass weeds later in the season. Dr. Webster says he leans more toward Ricestar if the problem is predominantly sprangletop and toward Clincher if it is fall Panicum. I agree with this approach. We have been advised by the local Ricestar representative to avoid the use of Rice-star on medium-grain varieties, especially in a water-seeded system. The label specifically states it should not be used on aromatic varieties.
In Clearfield rice systems, Beyond is rated seven by Dr. Webster on both species. Newpath and Clearpath do not provide satisfactory control. Other important grass weeds in rice include barnyardgrass, jungle-rice, broadleaf signalgrass and, occasionally, large crabgrass. Fortunately, we have not had the problems with herbicide resistance in barnyardgrass that other states have, so we still have several options for its control.
Dr. Webster and his group of graduate students have developed a computer program to key out rice weeds. It should be posted on the Web soon and be very helpful. Remember, rice herbicides work better with water.
Early insect control
Dr. M.O. “MO” WAY
Another problem is delaying the flush or flood after a soil-applied herbicide application. Most herbicides are activated by water, so delaying flushes or floods after application of soil-applied herbicides can dramatically reduce efficacy. Another potential problem is not following the stewardship guides for Clearfield rice. These guidelines are designed to delay the development of resistance. Evidence already indicates some resistance is developing in selected weeds and regions.
As far as early insect management is concerned, chinch bug, aphids, thrips, South American rice miner, fall armyworm and rice water weevil are potential culprits in Texas. All of these pests can be effectively controlled with current pest management methods and tools, but SCOUTING is essential to determine if these pests are present and damaging. For chinch bug, an average of one adult per two seedlings justifies a control measure. In checking for chinch bug, wiggle the seedling from side to side and watch the soil area around the culm. Often, chinch bugs will be below the soil surface, particularly during the heat of the day, where they feed on the plant.
For fall armyworm, simply inspect foliage for larvae that are quite small when young, but quickly grow to about 3/4 inch before they pupate. Rice can withstand a lot of defoliation, but when seedlings are small, even a little defoliation can retard plant development. A general rule is to apply a control measure when 20 percent defoliation occurs and larvae are present.
Aphids and thrips have piercing-sucking and rasping mouthparts, respectively, so these pests remove fluids from the plant. Yellowish, stunted plants often harbor these insects. You may confuse this injury with herbicide phytotoxicity, salt problems or nutrient imbalances. Again, only scouting will determine the real cause.
The vast majority of rice water weevil eggs are laid under the water, but adults are present in fields before the flood. Thus, you can see adult feeding scars on rice foliage before the flood. If you see lots of scars before flood, look out – you probably need to treat for this insect pest. Dermacor X-100 rice seed treatment received a Section 18 in Texas for 2009. This product is highly effective against the rice water weevil, as are the pyrethroids when applied at the proper time. Recent research conducted by my project shows only two to three larvae per core justifies an insecticide treatment. I routinely find at least this many larvae in the majority of fields that I inspect.
The trend towards lower seeding rates and more expensive seed means farmers need to protect their initial investment. Last year in Texas, rice water weevil was severe in many low-seeding-rate fields. I estimate some fields lost over 1,000 lb/A in yield.
Finally, I want to thank Valent USA Corporation, in particular Drs. Greg Rich and Frank Carey, for hosting a very productive, informative meeting for U.S. rice scientists last month in San Antonio. Greg recently retired and will be sorely missed, but he has other full time jobs now – grandkid sitter, cook and Harley mechanic. Remember, just press the “Easy Button,” Greg!