We have received multiple phone calls over the past week about rice water weevils (RWW), and based on our observations, it is trending towards a bad RWW year. This should come as no surprise with this year’s mild winter.
Many fields that have been flooded in the last 10 days have major RWW scarring, to the point in some instances where stand was reduced. This is not a common occurrence but it does underscore how bad weevils are in some areas.
People have found severe scarring in fields that have yet to be flooded, and some of this has even turned up in the upper portion of row rice fields.
While this scarring from adult RWW feeding is usually superficial with no yield loss, it indicates that adults are present and active in the field. Unfortunately, weather conditions have delayed planting along with flood timing. Based on planting date studies, we have observed much higher RWW pressure in rice planted after mid-May.
Most rice planted in Arkansas is either treated with NipsIt or CruiserMaxx seed treatments, which are excellent on grape colaspis. However, efficacy of these products on RWW decreases 28-35 days after planting.
Although RWW pressure is higher in later planted rice, these plantings typically experience rapid growth, allowing us to flood within 3 weeks of planting, and 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 CruiserMaxx within 28-35 days after planting will reduce observed scarring. However, Dermacor and Fortenza will not affect scarring but will maintain better control of larvae.
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For rice going to flood past the 28-35 day window with CruiserMaxx Rice or NipsIt, a foliar application of a pyrethroid like Mustang Maxx, 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 to 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 RWW and staying vigilant with scouting and timely applications will be critical.
