This spring is shaping up to be another challenge. Some farms have received timely rains, but many have not. Much of the Arkansas rice has been flushed, and I am receiving a lot of the normal questions about the “reach back” potential of Command.
The first grass that normally breaks through Command is broadleaf signalgrass. In some fields where only sparse showers have occurred since planting, Command has been active enough to control barnyardgrass but has let some signalgrass slip through. In other cases, a crop of grass emerged before the Command received a rain or flush.
On early-planted rice, the emerged grass is signalgrass because it germinates in cooler soil temperatures than barnyardgrass does.
Once you get activating moisture on grasses that have emerged, the grass will tell you what is going to happen rather quickly. If it turns completely white and the new growth (if it makes any) remains white, the chances are good it will die.
If the new growth is green, even though the older leaves are white, watch closely. If it begins to grow, you will have to kill it. What I typically see in those situations is a lot of the grass will die, but enough survives to require treatment.
Broadleaf signalgrass is easier than barnyardgrass to control postemergence. Propanil alone is excellent up to the four-leaf stage. Both Ricestar and Clincher have excellent activity to that stage — perhaps a little larger. Facet alone can provide excellent control of one- to two-leaf signalgrass if you flush it in.
Many of the fields I walked in May last year had been through a similar environmental pattern and had one flush of tillering signalgrass along with scattered sedges and broadleaf weeds. In that situation I recommended a lot of Duet with 0.25 lb/A Facet. If yellow nutsedge was bad, I added Permit.
There are a lot of fields with emerged grass and uneven rice stands because some seeds were in moisture and some were in clods. That is a good place to add a reduced rate of Facet to an early postemergence treatment because you will likely need an extended residual period.
Another question I'm asked a lot is, “How long will Command wait on a rain?” It can be in the field a long time and still be active once moisture is received, but as the soil temperature warms, grasses emerge quickly. Anything that emerges before activation puts you back in the above scenario.
A lot of growers say, “I know you say flush, but I would rather spray if I have to.” Many wind up wishing they had flushed, or it doesn't rain and they wind up flushing anyway but too late to save the cost of additional herbicides.
That is a management decision for each individual and a lot of factors enter in. If you do not flush soon enough, then stay on top of the emerged grass and kill it before you get into a mess.
Ford Baldwin, Practical Weed Consultants. e-mail: email@example.com.