Arkansas Rice: Delayed Phytotoxicity Syndrome; Water Weevil Activity Is Booming

    Rice water weevil

    We’re having a heat wave, a tropical heat wave.  Close the door, you’re letting the bought air out.

    So we talked last week about wanting to go fast, but maybe we could slow down just a little there, Ricky Bobby.  The heat is now into overdrive, and while the rice is moving fast, it’s now impossible to stay caught up to it.

    A minor cooldown is expected on Sunday (88!), so you get that while you’re working on Father’s Day, but the majority of next week is full of 99-101 depending on where you’re standing.  But let’s be honest, at that point what’s a degree here or there?

    We are still two weeks away from the 4th of July, but this heat has me already looking toward that date for particular reason.  We have long considered getting a “4th of July rain” – really meaning a rain somewhere in that timeframe – as being make or break for getting us through the season.

    Given this early heat and dry conditions, getting an upcoming rain sometime in the next couple of weeks will be extremely critical – both for keeping up with rice water and for having water for our other crops.

    A bit of good news is that so far, we’re not really hearing anything on disease pressure.  So we’ve got that going for us.  Stay hydrated out there and take plenty of breaks – nothing will get done if you overheat, it’s not worth it.  Work through the morning, take a break during the hottest part of the day, then do some more in the evening.  We all know this, but reminders never hurt.

    Let us know if we can help.

    New on Arkansas Row Crops Radio this week: Weeds AR Wild Series, S2 Ep 17:  Optimizing Rogue Activity in Rice

    NOAA 7-day precipitation forecast

    Fig. 1.  NOAA 7-day precipitation forecast. Click Image to Enlarge

    Delayed Phytotoxicity Syndrome (DPS)

    A common theme over the past couple of weeks has been calls about delayed phytotoxicity syndrome (DPS) – sometimes called delayed phytotoxic shock.  Ultimately the rice is sick, and its from our herbicides that are usually safe.

    Rice News on AgFax

    The symptoms of DPS are patchy areas of rice that are dark and stunted with twisted and/or rolled leaves (onion-leaf).  You may also see “fish-hooking” of tillers near the base of the plant and affected tissue will be very rigid.  When conditions get very severe, the plants feel “crunchy” or stiff and brittle – you can feel it when you step on them.

    Common herbicides such as Bolero, Facet, and Propanil are the main culprits, but others can be involved.  Why?  After flooding, when the soil goes anaerobic, fungi alter the normally safe herbicides and make them toxic to the rice.

    The only real solution to getting these areas to recover is to drop the flood.  Getting oxygen back into the soil and to the plant roots is what will alleviate the problem and allow rice to grow out of it.  The more severe the injury, the more you will have to dry the field up.

    There has been nothing to suggest that this affects particular cultivars.  While we don’t do any screening for it – we’ve observed it on hybrids and varieties alike.  Management, soil conditions, and environmental conditions play a role in whether it shows up and how severely.

    Delayed phytotoxicity syndrome (DPS) from herbicides applied to rice

    Fig. 2.  Delayed phytotoxicity syndrome (DPS) from herbicides applied to rice.

    Rice Water Weevil Activity is Booming

    Over the past two weeks we have received multiple phone calls on rice water weevil (RWW) showing up in large numbers in rice that has just gone to flood.  We are seeing the same thing in our plots at Stuttgart, however not near to level of some the fields we have walked in the north part of the prairie or in northeast Arkansas this week.

    Keep in mind if you have a diamide seed treatment (Fortenza or Dermacor) I would not spray for weevils; however, if your seed treatment is a noenicitinoid (CruiserMaxx Rice or NipsIt), odds are you are outside of the 28-35 days after planting window to get good control of RWW.

    When scouting for RWW and trying to decide if an insecticide application is warranted, there are a few things we need to keep in mind.  These are:  1) how long have I been flooded, 2) is there scarring on the newest leaf material, and 3) are adults present.

    How long the permanent flood has been established before RWW move into the field can determine if we need to spray.  From what we have seen the past few years is that if we have been flooded for 15-21 days or longer before RWW move into the field, then the yield loss is far less than if they move into the field immediately after flooding.

    Leaf scarring from adult RWW does not cause yield loss but is rather an indicator that we have adult weevils in the field.  When scouting for RWW we need to look at the newest leaf material to determine how recent the feeding occurred.  Keep in mind that leaf scarring does not always correlate with the number of larvae present in the field.  This is why we prefer to look at leaf scars and adults to make a treatment determination.

    RWW adults are going to typically move into a rice field as soon as the flood is established.  Once in the field, it only takes the adults 3-7 days to mate and lay eggs.  Once eggs are laid, there aren’t many options left for control.  If we see scarring but no adults present, then an insecticide application at that point will not be beneficial.  If adults are present and easy to find this may warrant a foliar application.

    As far as control goes, you only have a few options.  If an insecticide is needed, lambda (Lambda-Cy) is about your only option.  As far as a preflood vs postflood timing, we have seen better control from a preflood standpoint.  With that being said, these are small plot tests that we can flood up in a matter of hours versus days.

    I would bet on a field that is going to take multiple days to flood, that most of the insecticide if not all will be broken down before the flood can be established.  As a last resort, but a very effective treatment for RWW (however not the most economical), fields can be drained to soil cracking.  This will kill the larvae and help protect yield.

    If you have any questions feel free to reach out to us.

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