April 11 2011- Rice water weevils and colaspis in Louisiana rice

5/26/2011 11:16:54 PM

Picture 1: Rice water weevil adult on a rice leaf.

Picture 2: Rice water weevil adult feeding scars. If these are present, then weevils are or were in the field.

Rice water weevils and colaspis in Louisiana rice

 Originally posted April 11, 2011, by Natalie Hummel on Louisiana Rice Insects

On Friday I headed out to scout rice in Jeff Davis Parish with County Agent Barrett Courville and consultant Rustin Gilder. We scouted a field where Rustin had found a single colaspis larva. After much time spent digging, we were not able to locate any additional larvae. Unfortunately with this pest, that is not confirmation that it was/is not in the field. The larvae may have pupated and emerged as adults, or we may have simply been searching in the wrong area in the field.

A video on how to scout for colaspis in rice can be accessed by clicking here.

The farmer planned to bring permanent flood soon. No insecticide seed treatments had been applied to the seed. Thus, due to the reduced stand from a combination of factors (poor germination, dry conditions and probably colaspis injury), we advised using a pyrethroid to prevent further injury from rice water weevils. Rice water weevils were already active in the field, as indicated by feeding scars on the leaves. To further complicate matters, there are crawfish ponds nearby. To avoid pesticide drift on the crawfish ponds, we suggested using Mustang impregnated on fertilizer both before and after application of permanent flood (based on scouting for adults after permanent flood). A strategy to control rice water weevils is particularly important in this situation, where the stand will be thin at the time of permanent flood and weevils are already actively feeding in the field. When the stand is thin, there tends to be a more severe infestation of rice water weevils.

During my discussions with the consultants and producers we met in the field, it sounds like a lot of rice is at or near permanent flood in southwest Louisiana. Many of the consultants also reported that rice water weevils were present in most of the fields. If you used a seed treatment (CruiserMaxx, Dermacor X-100 or NipsitInside), your rice should be protected from injury due to rice water weevil larvae feeding on the roots.

Keep in mind that if you plan to use a pyrethroid to control rice water weevils, it is important that the timing of the application is correct. The pyrethroid chemistries have a window of activity of about two to three days under ideal conditions. We recommend scouting for the presence of adults (Picture 1) and/or feeding scars (Picture 2).

A video on how to scout for rice water weevils in rice can be accessed by clicking here.

If adults and/or feeding scars are present in the field, you may consider using a pyrethroid to control the adults before they have a chance to lay eggs. Adult rice water weevils mate on the plants, and then the females swim below the surface of the water to lay their eggs in the leaf sheath below the water line. This is why it is important to kill the adults before they have a chance to lay eggs. Once the larvae hatch from the egg mass and swim down to the soil level to attack the rice roots, they can no longer be effectively controlled by a pyrethroid insecticide spray. Rice water weevils impact yield by feeding directly on the roots of the rice plants, causing pruning and negatively impacting the ability of the plant to take up soil nutients and produce an optimal yield.

Please contact your local county agent for more information about rice water weevil management in Louisiana.

As a final note, please send me an email if you find aphids or armyworms in rice in Louisiana. We need specimens for our laboratory colonies in Baton Rouge.

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