One question I get this time of year is how to kill volunteer rice from last year before planting. Several have asked about using high rates of 2,4-D as an early preplant residual treatment. My concern is the potential for rice injury and I question how effective it would be.
With normal burndown rates of 2,4-D, the plant-back wording on the labels vary. The rule of thumb has been to wait 30 days, although there have been some labels with intervals as short as 14 days. What little research I have seen shows that 14 days is usually sufficient.
However, that can depend on the time of year the studies were conducted. The warmer the soil is, the faster the herbicide will degrade. We are planting rice earlier and earlier, which can affect the intervals. While I know you can sometimes plant sooner and see no injury, I stick to the 30-day interval to be sure. If you plant too soon, it can be ugly.
The questions I have received about using 2,4-D for volunteer control have been at much higher-than-normal burndown rates, and this could extend the plant-back interval. I would not guess at what it should be. The common sense conclusion to me would be by the time the 2,4-D degraded enough to allow the safe planting of rice, it would allow the germination of volunteers as well.
My recommendation for controlling volunteer rice is glyphosate, and use 3 to 4 pints of the 4 pounds-per-gallon formulation or equivalent. Spray it far enough ahead to see the result at planting. If there is any green left in the plants at all, spray them again before rice emergence. From that point, you just have to live with what is left.
Ford’s philosophy of barnyardgrass control is to “load up before it comes up.” While it may be hard to keep spending money on grass you can not see, my experience the past few years is if you wait until you see it, you will spend twice that amount, or more, and still may cut a grassy rice crop.
Most weed control programs will begin with Command. There is a new formulation of clomazone entering the market this year from Cheminova called Alert. I am told it will be available in limited quantities pending federal registration. It has passed the Arkansas State Plant Board requirements for aerial application when the federal label is approved.
University of Arkansas and independent testing data I have seen comparing Alert to Command have shown comparable results. Until it is available, I will refer to clomazone as Command.
While Command is the primary residual herbicide to begin a program, I wish we had a comparable substitute with a different mode of action for resistance management purposes. A couple of possibilities in specific situations are Prowl plus quinclorac (we now have Facet, Quinstar and Ryzon as products containing quinclorac alone) or Bolero plus quinclorac. Both can provide excellent grass control as delayed pre-emergence treatments, which means the rice seed must have imbibed its germination water before they can be applied. This usually means a rain or flush is needed before application followed by a rain or flush after treatment to make them work.
The simplicity of the Command program and also the much cheaper cost at the time of its introduction resulted in Command being used on most of the rice acreage in Arkansas. The Command price has increased considerably while the quinclorac price has decreased, so the price difference is not as great as it once was. However, the Command programs are still simpler and have a much lower water requirement for activation.
If you can make the delayed pre-emergence treatments work on your farm they offer a herbicide rotation alternative to Command. If not, my recommendation is to begin the conventional and Clearfield program with Command at planting.