We have received multiple phone calls over the past week about rice water weevils (RWW). Based on our observation, this year is trending toward a bad RWW year, and most fields flooded in the last 10 days show major RWW leaf scarring.
While this scarring from adult RWW feeding is superficial and doesn’t cause yield loss, this is a sign that adults are present and active in the field.
Unfortunately, with the weather conditions we have had, planting has been delayed, along with flood timing. Based on planting date studies, we have observed much higher RWW pressure in rice planted after mid-May.
The bulk of the rice in Arkansas is either treated with NipsIt or CruiserMaxx insecticide seed treatment, which are excellent on grape colaspis. However, efficacy on RWW with these products decreases 28-35 days after planting.
Although RWW pressure is higher for later planted rice, these plantings typically grow rapidly and we can get to flood within 3 weeks of planting and still get sufficient control of RWW with NipsIt or CruiserMaxx.
For rice that is past the 28-35 day window going to flood, a foliar application of a pyrethroid like Mustang Maxx, Lambda-Cy, or Declare might be called for. Timing is critical on foliar applications for RWW. Applications must be made within 5-7 days of permanent flood establishment.
If it is later than that, our studies indicate you may as well keep the insecticide in the jug. To prevent weevil damage then, your only option is to drain the field until the soil cracks. Most growers aren’t crazy about doing that. It’s costly and may impact weed control and fertility.
Remember, late rice will have high populations of rice water weevil. Stay vigilant with scouting. Timely applications are critical.