I continue to be impressed with the level of weed control in this year's Arkansas rice crop. It has been common for fields to go to flood with only Command and a little broadleaf clean-up. Most growers should have far less money in their weed control program than they did last year.
In addition, not much flushing had to be done in most areas once the rains started. This all adds up to good news in a year when farmers truly needed it.
I wish we could stop inventing new ways to kill a crop or a neighbor's crop. This would make my job much less stressful. However that is a topic for a different day.
In spite of having a clean crop, there will be escaped weeds. It got pretty dry just ahead of flooding in some areas. This can affect preflood herbicide performance.
Do not just assume everything is going to die when the flood goes on. Monitor some areas in the field you know to be problem areas and kill grass that comes through the water.
There are three main herbicides used for postflood grass control.
I usually recommend Ricestar HT if the postflood problem is primarily sprangletop. I have found it to be most consistent on the sprangletops. If the sprangletop is the loose-head species, a 17-ounce rate is usually sufficient unless you are tank-mixing it with something. If so, use 24 ounces.
If the sprangletop species is tight-head (Christmas tree grass), use 24 ounces and don't tank-mix it with anything.
For postflood situations where grasses include a combination of barnyardgrass, broadleaf signalgrass and sprangletop, I usually recommend Clincher or Clincher plus Facet.
In situations where the grasses will still be relatively small (for a postflood situation) and the population is not severe, I usually recommend Clincher alone. It works best when you apply a shallow flood and apply it as soon as the flood is stabilized and the grass is exposed. This is usually five to seven days after flooding.
Then raise the flood level. The flood must be maintained for it to work.
For situations where the grass is larger or the infestation is severe, adding 0.25 pound (per acre) Facet to the Clincher makes it a much better treatment.
A crop oil concentrate at 1 quart per acre should be added to all Clincher treatments.
Where sprangletop is not a problem, 0.5 pound of Facet plus crop oil is still a good postflood treatment. I often choose it over Clincher if the grower is not sure the flood can be maintained.
Where the escaped grass is barnyardgrass only, I continue to hear good things both from the field and from my University of Arkansas counterparts on Regiment with the new surfactant system. If Regiment is used, do not apply it after green ring or severe injury can result.
I will not go into details on postflood broadleaf control. Most will be done with either Grandstand or 2,4-D. With Grandstand, a quart of propanil per acre needs to be added if hemp sesbania is present. Where indigo is present, Grandstand is the treatment of choice because all formulations of 2,4-D can be weak on it.
The main thing with any Grandstand or 2,4-D treatment is timing. Please scout early and make arrangements to get these herbicides applied toward the front of the application window.
I never get any midseason broadleaf calls until the rice is past the 0.5-inch internode elongation cut-off. Everyone pretty much knows what to use. However, my calls are always along the lines of “the weeds slipped up on me and my joint is already 2 inches, is it sill OK to put it out?” Those questions are very difficult and can be headed off with careful scouting.
Flooded fields are more difficult to scout properly. Keep in mind, however, all rice fields look good from the road when the fertilizer and flood are first applied. If not carefully scouted they can start heading in late June and none of our rice varieties head that soon!
Ford Baldwin, Practical Weed Consultants. e-mail: [email protected].