By Nick Bateman, Gus Lorenz, and Ben Thrash, Extension Entomologists
We have received multiple phone calls over the past week about rice water weevils and based on our observations, it is trending towards a bad rice water weevil year. This should come as no surprise with the mild winter we had this year. Many fields that have been flooded in the last 10 days have major rice water weevil scarring, to the point in some instances where stand was reduced. This is not a common occurrence and shows how bad weevils are in some areas. Severe scarring has also been found in fields that have yet to be flooded and some has even been observed in the upper portions of row rice fields.
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 rice water weevil 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 rice water weevil decreases 28-35 days after planting. Although rice water weevil 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 rice water weevil with NipsIt or CruiserMaxx. If rice has been treated with Dermacor or Fortenza, it will still have protection from rice water weevil 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 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. 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 rice water weevil and staying vigilant with scouting and timely applications will be critical.