- Specialists Speaking -
Since the loss of fipronil (Icon) as a seed treatment for insect control in rice, the search for a replacement has been slow, but diligent. Three new products are currently being evaluated for control of lespedeza worm (grape colapsis), rice water weevil and other insect pests of rice. However, understand that obtaining registration of these products by the EPA is a process, and, as it has been said, “the wheels of government turn slowly.”
Dermacor received a Section 18 emergency exemption label for use in the southern United States during the 2008 growing season. While the acreage was limited, it allowed us to see the performance of this product in several environments.
Based on work conducted by Dr. Gus Lorenz, we now know that Dermacor is very effective against rice water weevils but is not as effective as we need for controlling lespedeza worms. Averaged across several large-block field trials, Dr. Lorenz measured about 40 percent control of lespedeza worms with Dermacor. This, however, is still better than no control.
A positive characteristic of Dermacor is the enhancement of seedling vigor and the influence this seedling health has on grain yield. Dr. Lorenz applied for a Section 18 emergency exemption to use Dermacor in 2009, but the request was denied by the EPA. With persistence, we were able to obtain a state crisis exemption in 2009. The company expects to receive full registration of this product in 2010.
Cruiser is another product that has been evaluated, and preliminary work indicates that it provides excellent control of lespedeza worm. The company has expressed strong interest in labeling this product. As with Dermacor, Arkansas was denied a Section 18 emergency exemption, but Dr. Lorenz was able to convince the EPA that the lespedeza worms were enough of an economic threat to justify a state crisis exemption. In Dr. Lorenz’s small-plot studies, Cruiser has provided excellent control of lespedeza worms and rice water weevils and has resulted in increased grain yields.
The third rice insecticide seed treatment that is currently being tested and hoped to be labeled soon is Nipsit. This product has excellent activity against both lespedeza worm and rice water weevil. However, it is probably the farthest away from receiving full registration. Dr. Lorenz applied for a Section 18 for this product as well but was denied by EPA.
The good news is that several products will soon be available for Arkansas rice farmers to control the most important rice insects. Insecticide seed treatments have the opportunity to give growers peace of mind knowing that the rice is protected, and that they are obtaining the best control possible for their specific situations.
Dr. John Saichuk
What does Clearfield technology have to do with insect management? Because Newpath herbicide controls red rice, it eliminates the need to use water as a means of suppressing red rice. This makes it possible for farmers to use delayed flood water management instead of continuous or pinpoint flood water management systems. In dry years, herbicide application can be done with ground rigs; fertilizer can be applied to dry soil by trucks; and pumping costs can be reduced with delayed flood water management. Just as changing herbicides causes weed shifts, changing the environment affects the insect profile and insect management.
Prior to the advent of Clearfield technology, most of the rice in the southwestern part of the state was water-seeded to suppress red rice. Because water management was often the pinpoint flood system, or a modification of it, water was typically on the fields prior to planting and remained there until harvest. This practice provided an ideal habitat for the rice water weevil (RWW).
When insecticides could not or were not used to control RWW, the only option was to drain the field about 10 days prior to internode elongation (green ring) and allow it to dry thoroughly. Much discussion has surrounded this practice and its merits versus penalties to the rice crop. From an agronomic standpoint, it is not a desirable practice, but in some cases, it is the only option.
The practice of draining near mid-season requires that the field be dried thoroughly to be of real benefit. In wet years, it has been less than effective simply because the field does not dry out enough to affect larvae. There has been considerable debate about whether larvae (root maggots) are actually killed or simply slowed down to the point that rice plants can grow new roots. Most of the times when we have had to resort to this method in our verification program, the number of larvae per core return to the levels at which they were prior to draining very quickly. This leads us to believe very small larvae may be killed, but the larger ones survive and are just not able to feed as well as when the soil is flooded.
Research conducted by Dr. Mike Stout indicates delaying flood will delay RWW infestation, thereby reducing the injury they cause. This response not only is because weevils cannot lay eggs until there is standing water present but also because rice plants are larger by the time the infestation occurs. Larger plants can tolerate more feeding than young plants because they have a more extensive root system.
Last year, a few growers decided to take this practice to an extreme and delayed establishment of permanent flood until nearly mid-season. It was a mistake. In one case, it caused severe blast in a field of CL151. In Dr. Don Groth’s disease nursery, he encourages blast development by growing rice without a flood. In essence, the farmer created a “blast nursery” on his farm. Where CL151 was grown in a normal water management system, blast was not a problem. Based on observations in our verification fields, the sooner we can establish a flood, the sooner the crop will mature. Those who harvested rice both prior to and after the hurricanes last year can testify to the value of an early harvest.
With all of the current tools in the box to control the RWW, it seems to me that it is more risky to prolong flooding much beyond first tiller than to keep it dry to suppress weevils. Delaying flood to first tiller is in itself beneficial in reducing RWW damage, but beyond that point, the costs outweigh the benefits.
The point I am trying to make is that we readily accept changes in the weed spectrum when we change cultural practices or become too dependent on one herbicide. Changing cultural practices can influence insects, too. Some practices will reduce one pest while enabling another to build up. This is certainly true for the rice water weevil. Unfortunately, I do not think anything short of an atomic blast is going to slow down stink bugs, so it probably does not matter what we do, they will be here.
Water and insect
Dr. M.O. “MO” WAY
Good rice integrated pest management (IPM) is tied to water management. For instance, in Texas, chinch bugs and fall armyworms are often controlled by a timely flush, which effectively drowns many of the insects or forces them up on the plants where they are more vulnerable to predator, parasite and chemical attack. Predators of fall armyworms include birds (cattle egrets), wasps, lacewing larvae and assassin bugs.
Parasites include various species of small wasps, which lay eggs in fall armyworm larvae. The eggs hatch and devour the host caterpillar.
Chinch bugs do more damage when they feed near and below ground level. We did experiments to prove this, so if the bugs are moved up the plant by a flush, damage is not as severe. When checking for chinch bugs, wiggle the plant from side to side, and often you will see the bugs feeding below ground level on the roots of the rice. A real bad sign is if you see the adults and the orange nymphs. This means the bugs are multiplying in your field, and control is probably needed. The economic threshold is only one adult chinch bug per two seedling rice plants.
Other seedling pests include thrips and various species of aphids. The worst of the aphids is the yellow sugarcane aphid, which is a bright lemon color and can be found on young rice leaves either on the top or bottom sides. This aphid injects a toxin into the seedling, which causes the leaves to turn an orange to red color. Plants are stunted and tend to rosette – produce more side tillers and leaves. All of the above pests can cause significant stand loss. I know I sound like a broken record, but as soon as your rice emerges, begin scouting and do so frequently. These seedling pests can do a lot of damage in a short time period, which is largely due to the small size of the plants.
Water management also can eliminate certain insect pests. Rice seed midges are aquatic insects whose larval stages feed underwater on germinating rice seeds. Tadpole shrimp, which do not occur in southeast Texas, but are common in California and were recently found in Missouri rice fields, also are aquatic. These pests dislodge rice seedlings and cause them to float. Thus, dry seeding and delayed flooding will eliminate these pest problems. If you water-seed, using a pinpoint rather than a continuous flood will help minimize problems caused by these pests.
In addition, my ex-graduate student, Becky Pearson, recently found a common aquatic beetle called a water scavenger beetle that can uproot rice seedlings through foraging and egg-laying activities. This damage can be eliminated by switching to dry seeding and delayed flooding. Speaking of delayed flooding, the rice water weevil is more problematic when the time from rice emergence to application of the flood is shortened. Our research has shown delaying the flood five weeks and longer can reduce rice water weevil damage.
But, in general, I believe the benefits of applying an early flood in relation to emergence outweigh the benefits of delaying the flood to reduce rice water weevil damage. I don’t recommend draining fields mid-season to control this pest. However, we do have many effective tools to control this pest.
As you probably know, one of these tools is the seed treatment Dermacor X-100, which received a Section 18 in Texas for this year. I thank Ed Gage with TDA and Tony Britten and his colleagues with EPA for their hard work on this registration. Recent research from my project shows only two to three rice water weevil larvae per core justify a control measure. Most untreated fields I sample have at least this larval density. In other words, the economic injury levels for this insect are very low. Our data show typical yield increases due to controlling rice water weevil average between 300 and 500 lb/acre. Our data also show Dermacor X-100 will control stalk borers and South American rice miner, but not chinch bug and other insects with piercing-sucking mouthparts.
If you have questions or want more information, call me at (409) 658-7394 or email firstname.lastname@example.org. In the meantime, put on your rubber boots, get out your hand lens (if you want a hand lens, let me know), sharpen your pocket knife to dissect plants, get a digital camera (does not have to be expensive), make sure you have a sweep net, carry some plastic sandwich bags and a bucket, secure your cell phone (if you are like me, your cell phone may take an occasional swim) and vow to do a better job of scouting your rice this year. It will pay off in money, less disruption to the environment and reduced stress on you! Have a successful 2009 rice crop!
Early season pests
Dr. LARRY GODFREY
“Out of sight, out of mind.” We have all heard this expression. While it may apply to some situations, it should not be practiced in terms of management of early season insect pests in rice.
These pests can rob rice growers of yield even though they are “out of sight” during most of the season. Management plans should be carefully developed.
In California, early season pests include seed midge, crayfish and tadpole shrimp (these latter two pests are not actually insects but are related organisms called invertebrates). These pests reduce rice stands at, or soon after, seeding.
Rice water weevil is the most important insect pest of rice in California, and management plans for this pest should also be designed and conducted within the first three weeks after seeding. The damage from rice water weevil occurs from the larvae feeding on the roots during the mid-season period, but the current management approach for this pest in California is targeted at the adult stage. Thus, you need to consider this pest when developing early season management plans. Unfortunately, all of these pests are difficult to see, which makes management challenging.
How can infestations be determined?
Past history of the field, field symptoms, environmental conditions and observations can all be used to evaluate “populations.” Seed midge and tadpole shrimp infestations develop very fast and occur at the soil surface of the flooded fields. Delayed germination, poor stand establishment, floating seedlings and abnormally muddy water could be indications of infestations. Weather conditions that hinder early season seedling formation could also be a “clue.” Quick determination of these infestations and rapid management actions can save a stand.
The reason rice water weevil management is directed at the adult stage (corresponding to the two- to three-leaf rice stage) is because there are no insecticides registered in California with activity on the damaging larval stage.
Visual monitoring of adult water weevil infestations is very difficult. To aid in making the treatment decision, a floating barrier trap was developed at the University of Arkansas and adapted to California conditions. Use of this trap during the first seven to 10 days after flooding can help classify fields as needing treatment or not. In addition, certain areas and fields historically have rice water weevil infestations; weedy levees and neighboring natural vegetation areas also can promote infestations.
Therefore, plan now for early season insect pest management. Insecticide application windows are narrow and must be made under the proper environmental conditions and with consideration of water-holding requirements, so good planning is critical.
As questions arise, contact specialists and county advisors at http://www.ipm.ucdavis.edu/PMG/selectnewpest.rice.html.
Dr. Nathan Buehring
Water management is very critical in maximizing rice yields. Being efficient and effective with water is necessary for weed control, preventing nitrogen loss and maximizing grain fill. Therefore, it is a highly effective input that is used throughout the season to help rice growth and development, while also increasing the effectiveness of herbicides and efficiency of nitrogen fertilizer.
Flushing is a key component in making herbicides work if no rainfall is received after the application. Command, Facet and Newpath are some of the herbicides that have to be activated by moisture to work. To keep these herbicides active in the soil, moisture is also required. As a result, deciding not to spend another $5/A on flushing and waiting on a rain can add another $30/A in herbicide cost that will only result in mediocre grass control.
Getting the flood established in a timely manor is another critical component to getting the most out of expensive nitrogen. To reduce the amount of nitrogen lost to volatilization, the flood needs to be established within five days after the application. Allowing the urea to sit on the ground for any time after that will prevent you from maximizing your rice yields.
Using Agrotain will protect your urea up to 10 days after applications. If you know up front that it will be five to 10 days before you can get the flood established, I would strongly encourage you to use Agrotain. It is a small input that will help protect a big investment.
Once the flood is established, I would focus on maintaining a two- to four-inch flood during the rest of the growing season. This is very critical the first two to three weeks after flood initiation because this will prevent any weeds from emerging and nitrogen loss. If the flood is not maintained for some reason, nitrogen volatilization will not begin until the soil begins to crack. As long as it is still muddy, you are fine, but I would begin pumping it back up immediately.
Our recommendation still calls for draining at 1/2 of the panicle straw color on clay soils and 3/4 of the panicle straw color on silt loam soils. On clay soils that do not drain and dry quickly, you may drain those a few days earlier than recommended so that you will not be rutting up the field at harvest.
Water is a necessary and costly input for rice production. Therefore, I would look at the most efficient way to manage water to get the most out of your production dollar.