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Sprangletop increasing in rice fields

Look for ways to get more than one soil residual herbicide applied and activated in rice before any barnyardgrass emerges.

I have mentioned tighthead sprangletop in a couple of articles. That weed is increasing and is one you need to stay on top of. Most of the herbicides we are using are somewhat weaker on this sprangletop than on loosehead sprangletop. Therefore we are pushing a species shift toward the tighthead species.

As continuous rice is grown, especially in zero-grade fields, sprangletop is becoming more prevalent and more difficult to control than barnyardgrass in some of those fields.

Ronnie Helms recently related a story about his rice situation. He grows all zero grade continuous rice and was looking to rotate from Clearfield back to a conventional variety on the farm. He had applied only one Newpath application last year in hopes he could get by with planting conventional rice with no carryover injury.

To be on the safe side, he pulled samples and sent them for analysis. I had told him when he pulled the samples, “if they test high that is good information. However, if they test low you still may not know what will happen until you plant the rice.” They tested through the roof so he simply can not risk planting the farm in a conventional variety.

Newpath breaks down by photodegradation and by microbial degradation. It goes against conventional thinking that it could possible last longer in the soil in a rice field environment than when used in soybeans as Pursuit. However, anaerobic soils have little microbial activity going on. Therefore, the wetter the soil stays, the more slowly the herbicide degrades.

Zero grade fields tend to stay wet and we had a wet winter. Last year was also a year with a lot of cloudy weather. Ronnie’s example does not mean the same thing has occurred in every other field. It is a red flag that should not go unnoticed if you happen to be thinking about trying a field of conventional rice behind Clearfield. It is a crapshoot anyway and we could have just had a fall and winter that would make it an even greater risk.

Getting back to sprangletop, I suggest using the split application of Command in the problems fields. The problem fields would also be a good place to apply Command as a pre-emergence treatment and then follow with Bolero, Bolero plus Command, or Bolero plus Prowl as a delayed pre-emergence treatment.

It is scary to have to over-depend on Command and/or Ricestar HT or Clincher for tighthead sprangletop control. The university guys have tested some sprangletop populations with unreal resistance to Ricestar HT and Clincher.

Get a good residual program out up front so you do not have to continuously go to these two herbicides to bail the field out.

With the cold, wet spring last year, the situation was tailor-made for Ricestar HT for early postemergence grass control. It has been interesting to watch that product from near death to one of the primary “go to” herbicides. The class of chemistry with Ricestar HT and Clincher is another that must be protected.

We are more dependent upon them each year, but that class of chemistry has shown that, like the ALS inhibitors, it can blow up quickly. When the grass breaks early and you go to Ricestar HT, always have another mode of action in the tank with it.

The second application of Command in a split works well with it — especially if sprangletop is an issue. For barnyardgrass, quinclorac or the quinclorac/Aim herbicide (Broadhead) make nice mixes with Ricestar HT.


TAGS: Rice
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