The tough time of the season for rice weed control has arrived. While there are a lot of very clean rice fields across Arkansas, consultants are struggling with late-emerging weeds in a lot of fields.
When extremes in environmental conditions occur, weed control is simply more difficult. We have hit the time of the season, just like last year, when herbicides just are not working as well as they did earlier.
Another factor making things difficult is many growers found themselves way off schedule planting both rice and soybeans. This has resulted in more difficulty getting some of the first or second choice herbicides applied due to adjacent susceptible crops.
In some cases things are further complicated by herbicide shortages.
Now, the theme of most calls is, “How late can I apply this herbicide or that herbicide?” When you start getting those calls, the weeds have “blown out the top” and it is probably past the time most herbicides should be applied.
The labeled cut-off on some of the commonly applied late-season herbicides are as follows: Clincher and Grasp, 60 days prior to harvest (PHI); Ricestar HT, 65 day PHI; Facet and Quinstar, 40 day PHI; Regiment, joint movement; 2,4-D and Grandstand, 0.5-inch internode elongation; and Beyond, 14 days past internode elongation.
On the Clearfield hybrids there remains an injury concern when Beyond is applied later than green ring. Herbicides that burn such as Blazer or Aim should not be applied after the flag leaf has emerged.
The late-season shortage of Facet has resulted in several calls about Quinstar herbicide. It is a generic equivalent to Facet and is available in a 75DF formulation like Facet and a 4-pound per gallon flowable formulation (4F). Quinstar has performed equal to Facet in efficacy studies conducted by University of Arkansas weed scientists, and also in the drift studies required by the Arkansas State Plant Board to register the herbicide in Arkansas.
The weed of the week is tighthead sprangletop, sometimes referred to as Christmas tree grass. This weed concerns me for several reasons. We are selecting for it because herbicides such as Command, Ricestar HT and Clincher are not as good on it as they are on loosehead sprangletop. We are also selecting for it because Newpath is weak on it in Clearfield rice.
I am also concerned because resistance to Clincher and Ricestar HT has been documented in Louisiana.
Most of my late-season calls have been on this weed. Some callers ask if I prefer Ricestar HT or Clincher to control it. Both can work and both can be erratic. My first choice treatment is 24 ounces of Ricestar HT (do not tank mix it with anything other than perhaps Facet or Quinstar).
However, I have recommended Clincher is a lot of situations this year as well.
I have had several calls where tighthead sprangletop has been missed by Ricestar HT or Clincher. Those do not concern me too much from a resistance standpoint because this weed is just hard to kill. However, I have had some calls where it has either been missed twice with Ricestar HT or Clincher or with one application of each herbicide. I suggest in those situations to harvest some seed to have Jason Norsworthy at the University of Arkansas test for resistance.
I am concerned over the rapid increase in this weed as we have a small number of herbicides with activity on it and in some cases even those are not working very well.
The weeds are talking, is anybody listening? We need new weed control technology in rice now.
I would also remind you that we have a lot of soybeans to be sprayed with rice in the reproductive stage of growth. We have had a lot of drift problems with a lot of different herbicides already this year. We do not need glyphosate on rice in the reproductive growth stage!
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