| [Image: rww lifecycle] |
| [Image: rww damage to rice crop] |
|
RWW biology and management
The rice water weevil is the most important early-season insect pest of rice in Louisiana. Adults of this insect emerge from overwintering sites beginning in early April in southern Louisiana (later in northern Louisiana) and fly to rice fields, where they feed on young rice leaves. This form of injury is not economically important except under unusually heavy infestations or prolonged cold periods when rice grows at a slow rate.
Egg-laying commences when standing water is present in a field that is infested with adults. This condition is usually met immediately after a permanent flood is applied to a field. Young rice is preferred for oviposition. After eclosing from eggs, larvae feed under water on rice roots and pass through four larval instars and a pupal stage in approximately 30 to 40 days. The rice water weevil is the most injurious insect pest in Louisiana rice production. Yield losses in excess of 25% can occur from severe infestations.
More information about rice water weevil biology and management can be found at this link
How does the rice water weevil damage the rice crop?
Rice water weevil adults feed on rice leaves, causing longitudinal scars. Some people describe the white stripes on plants as “painted” rice. If the weevil population is large enough on small seedlings, this can result in death of the plant. Immediately after the application of flood water to the rice field, adults will begin laying eggs just below the surface of the water. If you did not treat your rice with Dermacor X-100, you need to use an insecticide that will kill adults before they have the chance to lay eggs.
Complications with crawfish production
Remember that if your field is located near a crawfish pond you need to use extreme caution when applying insecticides by plane or ground rig for RWW control. Pyrethroid insecticides (Karate and Mustang) are extremely toxic to crawfish. Trebon 3G is also toxic to crawfish, but it is a granule and is less likely to drift into nearby ponds. Do not apply insecticides to a rice field that will be used for crawfish cultivation. Be sure to read and obey any label restrictions for any insecticide applied to your rice field.
Scouting rice for rice water weevil adults
If you treated with Dermacor X-100, there is no need to scout for adult RWW. You may want to pull core samples and check roots for presence of larvae 2-3 weeks after establishment of permanent flood. If you will need to apply an insecticide for RWW management, then check 10 locations in the field every 3-4 days. Treat when adults are present or feeding scars are observed and when conditions are favorable for egg laying (water is present or will be present soon). Scout again beginning 5-7 days after insecticide application. More than one insecticide application will be necessary.
More information on RWW scouting can be found here
Insecticide options for RWW management in Louisiana rice production
This test will compare the larvacide and adulticide treatments, as well as evaluate the timing of treatment. The larvicide, Dermacor X-100, is a seed treatment that is registered under a Section 18 registration in Louisiana. The use of this insecticide is restricted to rice planted into a dry seedbed -- either drill seeded or dry broadcast. The adulticides that are labeled for use in Louisiana rice include Trebon 3G, Karate Z, Mustang MaxEW, Prolex, Silencer and Proaxis. The adulticides can be used at different timings, depending on grower preference. Pyrethroids can be applied as a foliar spray (Karate Z, Mustang Max EW, Prolex, Proaxis, Silencer), impregnated on fertilizer (Mustang MaxEW) or as granules mixed with fertilizer (Trebon 3G). An ovicide, Dimilin 2L, can also be used for RWW management in Louisiana.
Table 1. Insecticides that are currently labeled for use to control RWW in Louisiana rice.
|
Treatment |
Rate |
Application Timing |
|
Dermacor X-100 |
Seeding rate dependent |
At planting |
|
Trebon 3G |
6 - 9 lb./acre |
Immediately before or after permanent flood |
|
Karate Z |
1.6 - 2.56 fl. oz./acre |
Immediately before or after permanent flood |
|
Mustang MaxEW |
3.2 - 4.0 fl. oz./acre – applied as foliar spray or impregnated on fertilizer |
Immediately before or after permanent flood |
|
Prolex |
1.28 – 2.05 fl. oz./acre |
Immediately before or after permanent flood |
|
Proaxis |
3.2 – 5.12 fl. oz./acre |
Immediately before or after permanent flood |
|
Dimilin 2L |
Depends on water or drill-seeded use |
See Louisiana Insect Pest Management Guide |
The 2009 Louisiana Insect Pest Management Guide can be found here
Treatments included in 2009 RWW demonstration test
This test will compare the larvicide and adulticide treatments, as well as evaluate the timing of treatment. The larvicide, Dermacor X-100, is a seed treatment that is registered under a Section 18 registration in Louisiana. The use of this insecticide is restricted to rice planted into a dry seedbed -- either drill seeded or dry broadcast. The adulticides that are used in this test include Trebon 3G, Karate Z, and Mustang MaxEW. The adulticides can be used at different timings, depending on grower preference. Pyrethroids can be applied as a foliar spray (Karate Z, Mustang Max EW), impregnated on fertilizer (Mustang MaxEW) or as granules mixed with fertilizer (Trebon 3G). Our test was designed to compare a single pyrethroid application either before or after permanent flood to two consecutive pyrethroid applications.
Table 2. Insecticide treatments and application timing in 2009 RWW demonstration trial
|
Treatment |
Rate |
Application Timing |
|
Dermacor X-1001 |
Seeding rate dependent |
At planting |
|
Trebon 3G2 |
9 lb./acre |
Immediately before permanent flood |
|
Karate Z |
2.56 fl. oz./acre |
Immediately before permanent flood |
|
Karate Z followed by Mustang MaxEW3 |
2.56 fl. oz./acre & 4.0 fl. oz./acre |
Immediately before permanent flood & 7-10 days post-flood |
|
Mustang MaxEW |
4.0 fl. oz./acre |
2-3 days post-flood |
|
Untreated Check |
No insecticide |
Not applicable |
1Applied to seed by certified treater, rate depends on seeding rate. 2Mixed with fertilizer and applied before permanent flood. 3Impregnated on fertilizer.
The most important thing to keep in mind when making your decision about RWW management is that you need to consider what you are trying to control. To prevent egg laying, you need to control adults. If your treatment is delayed until after RWW adults have laid eggs, then you will not be able to control the larvae. If you miss the window of treatment and begin to see root pruning, then your only option is the drain the field. We are not sure why draining is sometimes effective, but it may be that drying up the soil around the roots stops weevil larvae from damaging roots. The removal of water from the field also stops further oviposition.
Table 3. Location of 2009 RWW demonstration fields
|
Location |
Cooperator |
RWW Treatments |
|
Rayne, La -- Acadia |
Darryl Hoffpauir |
All 6 |
|
Gueydan, La -- Vermillion |
Richard Hardee |
All 6 |
|
Ville Platte, La -- Evangeline |
Kenneth LaHaye |
All 6 |
|
Monterrey, La – Concordia |
Dale Denais |
All 6 |
|
St. Joseph -- Tensas |
Rusty Ratcliffe |
All 6 |
|
Rice Station -- Acadia |
Larry White |
Dermacor X-100 & check |
|
Lake Providence – East Carroll |
Terry Palmer |
Dermacor X-100 & Pyrethroid |
|
North of Crowley – Acadia |
Fred Cramer |
Dermacor X-100 Strip Trial & check |
|
North of Crowley – Acadia |
Fred Cramer |
Dermacor X-100 & check |
|
Welsh – Jeff Davis |
Mark Pousson |
Dermacor X-100, pyrethroid & drain |