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Rice weed control may require creative approaches

We have a grape colaspis (lespedeza worm) epidemic in some rice areas of Arkansas — especially on the Grand Prairie. Consultants and University of Arkansas entomologist Gus Lorenz are telling me they have never seen larvae numbers so high in some fields (up to 11 larvae in 6 inches of row).

In high numbers they can take a stand out in a matter of a few days. Stay on top of the situation and get help if needed.

The University of Arkansas recommendation is to flush in 100 pounds per acre of ammonium sulfate. Some are also flushing in some Mustang Max, which can provide some level of control if flushed immediately.

Farmers in the wettest areas of the state have finally been able to get in fields and some are getting rice planted any way they can. This may make for some interesting weed situations later, but we will figure out some way to get most of them cleaned up.

Unlike most other years, there has been no consistent pattern to the telephone calls I have been getting. This is likely because the situation varies so greatly from one area to the next, and these areas often are in close proximity to each other.

In situations where farmers were able to get in fields and planted early, residual herbicides have worked fantastically and many of those fields are in excellent shape.

I am getting some calls where residual herbicides are beginning to break and treatments are needed to carry the field to flood.

First, my rule of thumb is not to flood up on any existing grass. You can often control small broadleaf signalgrass or crabgrass with the flood, but you must hold the water over it. If you have one hiccup in water management, you will have escapes.

If the grass complex includes barnyardgrass, sprangletop or fall panicum, it will come through the flood regardless of how small it may have been when you covered it with water.

The herbicide treatment you need to go to flood with will obviously depend on the situation. With the grasses, just make sure there is nothing there but rice and soil when you flood.

I recommend a lot of propanil plus quinclorac (Facet or Quinstar) and Ricestar HT plus quinclorac for preflood treatments.

Regiment can also have a fit when the only grass is barnyardgrass.

Judging from the telephone calls I am receiving, this seems to be a nutsedge year, which usually requires some Permit in the mix. With broadleaf weeds, you can sometimes decide whether to clean them up preflood or wait until midseason. As a general rule, you never mess up taking out a stand of weeds.

With weeds such as groundcherry or smartweed, you have to kill them while they are small or not at all.

With coffeebean, indigo and morningglories, I sometimes recommend flooding up on them if a midseason application is going to be automatic anyway. I get a lot of calls, especially on indigo, where Grandstand will not or can not be used at midseason. In those cases you have to take them out with the preflood treatment.

If you are using quinclorac preflood and you want to get residual control on coffeebean and indigo, my favorite rate is 0.5 pound per acre. This is often higher than you may need just to get you to flood on grasses.

I have written in several articles that Permit obviously has more residual activity than we have given it credit for in the past. In some of the fields, especially where you have nutsedge anyway, for residual control of coffeebean and/or indigo, try some Permit at 1 ounce per acre on a trial basis. Again, this is a higher rate than sometimes needed for nutsedge control, but I would be interested in any feedback you can provide on whether or not a midseason treatment was needed for coffeebean or indigo following a 1 ounce rate preflood.

Weed control in some of this “plant it any way you can” rice that is going on now will be a throw-the-book-out deal. Call if I can help.


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