• By Nick Bateman, Gus Lorenz and Ben Thrash •
Our rice water weevil plots went to flood two weeks ago, and RWW activity has been extremely low. These plots are located in Stuttgart, where RWW pressure is low to moderate in most years.
Looking at these plots this week, the weevil scarring has increased quite a bit, with a lot of RWW adults present in the field. We have also observed this for multiple fields around RREC that we have been monitoring for the past few weeks. It is still early to make a prediction on how bad RWW will be this year, but this has been the trend we have observed over past two to three years.
While this scarring from adult weevil feeding is usually 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 rice planted in Arkansas is either treated with NipsIt or CruiserMaxx seed treatment, which are excellent on grape colaspis. However, efficacy of these products on RWW decreases 28-35 days after planting.
Although RWW pressure is higher for later planted rice, these plantings typically experience rapid growth allowing us to flood within 3 weeks of planting. In these situations, we still get sufficient control of RWW with NipsIt or CruiserMaxx.
If rice has been treated with Dermacor or Fortenza, it will still have protection from RWW at least 60 days after planting. Also, it is important to note that NipsIt and Cruiser within the 28-35 days after planting will reduce scarring observed. However, Dermacor and Fortenza will not affect scarring but will maintain better control of larvae.
For rice that is going to flood past the 28-35 day window with CruiserMaxx Rice or NipsIt, a foliar application of a pyrethroid like Mustang Max, Lambda-Cy, or Declare might be called for. However, Dermacor and Fortenza will NOT need a foliar application.
Timing is critical on foliar applications for rice water weevil. Applications must be made within five-seven days of permanent flood establishment, as long as adults are present.
If it is later than that, our studies indicate you may as well keep the insecticide in the jug.
Your only option then is to drain the field until the soil cracks to prevent weevil damage.
Most growers aren’t crazy about doing that as it is costly and may impact weed control and fertility. Remember, late rice will have high populations of RWW, and staying vigilant with scouting and timely applications will be critical.
Drs. Nick Bateman, Gus Lorenz and Ben Thrash are University of Arkansas Extension entomologists.