I had a much higher number of calls this season on tighthead or Amazon sprangletop in rice. A lot of callers commented that they had never seen it in those fields before.
In many cases the sprangletop broke through late in the season. When it blew out the top, a common comment was “where did it all come from?”
We have two primary species of sprangletop in Arkansas rice fields. Until now the more common species has been loosehead or bearded sprangletop. It is easily identified by its long wispy leaves that are pale green with a distinct white midrib and very distinct long ligule in the collar region of the leaf.
Upon emergence, loosehead sprangletop may be 3 to 4 inches tall yet still in the two-leaf stage. When it heads, the panicle is very loose and has no discernable shape to it.
This sprangletop species is also relatively easy to control with pre-emergence applications of Command or postemergence applications of Ricestar HT or Clincher.
The second sprangletop species and the one that gave everyone fits this year is tighthead or Amazon sprangletop. The leaves of this species are wider and brighter green than the leaves of loose-head sprangletop.
Like loosehead, it also has a distinct, long membranous ligule.
The growth habit and general leaf and plant shape of tighthead sprangletop resembles that of barnyardgrass much more than that of the other sprangletop species. When I am trying to do “over-the-phone” weed identification (which seldom works) and suspect tighthead sprangletop, I ask, “Does it look like barnyardgrass with a ligule?”
When this species heads, the panicle is much more compact than the loosehead.
Some must think it resembles a Christmas tree because Christmas tree grass is a commonly used name out in the countryside.
While we have always had this species in rice and while it has been the common species in a few areas of Arkansas, I certainly saw a lot more state-wide this year than before.
Where did it all come from? I do not know that I have all of the answers, but I will offer a couple.
First, sprangletop species are saturated-soil germinators. It was a frustrating experience as a weed researcher trying to do sprangletop control work. If I collected seeds and planted them in plots, they wouldn't germinate.
A typical farmer's response was “come get some of mine!” Even when we went to a farmer's field that had a sprangletop problem the previous year, we could almost count on getting no sprangletop up in the test, because sprangletop seeds germinate only when the soil moisture situation suits them.
If it is extremely wet early in the season, sprangletop may germinate and emerge with the rice. If it isn't wet but the field gets wet or you flush later, the seed may germinate later in the season and catch you off guard.
Sometimes you may have had a problem the last time the field was in rice, but you get no sprangletop up the next time.
It was extremely wet early this year, and that is one reason we likely had so much more pressure. I suspect that is why we had more sprangletop in general and could even be a reason we had more of the tighthead species.
Another reason we may have had more tighthead sprangletop is it is more difficult to control with most rice herbicides. Command is the most effective pre-emergence herbicide for sprangletop and it is rated equal on both species. However, there sure seemed to be more breakthrough of tighthead than loosehead with Command this year.
Newpath, Clincher and Ricestar HT are all rated as being weaker on tighthead than loosehead. For this reason we may simply be shifting the predominant species to tighthead with the herbicide programs available.
Next week I will offer my ideas for better sprangletop control. Just because this year was a “sprangletop year” does not mean next year will be. However, we sure put plenty of seed in the soil bank this year.