Shattered Clearfield rice fields
Apr 22, 2009 10:05 AM,
By Bob Scott
Extension Weed Specialist
University of Arkansas
Last year two hurricanes caused many rice fields to shatter across the Mid-South, a problem we have faced before. Typically it makes for poor yields and a good duck season. This past year event has caused a little more concerned than normal due to the fact that much of the downed rice was Clearfield rice or, worse, hybrid Clearfield rice.
When a field of Wells goes down or shatters, the rice that emerges the following year is Wells. Cultivated rice is not very weedy. It tends to try and germinate whenever possible; it does not overwinter well; and if it comes up volunteer in a field of Wells, oh well, it’s Wells, so we just farm it.
This may not be the case with all Clearfield volunteers.
First, with the conventional Clearfield varieties (CL161, 151, 171, etc.), there are two major concerns. Number one is that the volunteers from these fields will carry the CL trait. So if you do not rotate these fields to soybeans, you may have volunteers emerging at different times, increasing the window for out-crossing this year.
Second is out-crossing from last year. Normally most of the CL rice grown, and thus a large percentage of potential out-crosses with red rice, are hauled off the field. If a field lodges or shatters, these potential out-crosses stay in the field.
If this out-crossing occurs, you will get an F1 hybrid plant. This plant will be a large, vigorous plant that matures late in the season.
We have already observed this at numerous locations in Arkansas over the past few years. Because these plants mature late, they are often destroyed before they have a chance to mature and make seed.
If allowed to go to seed, the F2 generation would be quite variable and potentially weedier in nature. You could see seed dormancy, wide germination windows and maturity dates.
This brings us to the shattered hybrid Clearfield fields. When you plant a hybrid variety you are planting the F1. You cannot save this seed to plant back the following year. One reason is because it is illegal to do so; another reason is that it will not reproduce the same plant.
In fact, in the F2 populations we have observed numerous biotypes of plants that are throwbacks to the parental lines that created the hybrid. Some are short, some tall; some mature early, some late.
Weed potential
The potential to have a more “weedy” acting off-type is higher with hybrid rice than with conventional in year one and beyond, at least in theory. This has actually not been documented yet.
At least 25 percent of the volunteer F2s from Clearfield hybrid rice will tolerate Newpath herbicide or carry the CL gene. If the hybrid rice out-crossed with red rice, the genetic diversity could be much higher and more difficult to identify in year one.
The biggest concern with shattered hybrid rice is the presence of out-crossed red rice. The second concern is that a CL F3 plant may act as a weed, that it could germinate a little later in the season and mature early, before it can go through the combine.
I must stress that these are concerns at this point, theory only. We have not really tested this scenario completely.
I heard last fall that shattering and lodging amounted to anywhere from 10 to 100 bushels of rice on the ground in some fields.
With no research to support my recommendations, I recommend that the most severely shattered fields, especially those in hybrid Clearfield rice, be planted to soybeans for one year to clean up any volunteers or potentially out-crossed red rice plants.
I know that for some of you, soybeans are just not going to happen. In that case, I suggest planting a little bit later and allowing one “flush” of volunteer rice or red rice to come up. Spray it with about 2 quarts per acre of glyphosate, and plant back into that.
Plant hybrid
It would probably be wise to plant a hybrid (maybe at a slightly increased seeding rate) in that situation, due to the competitive nature of hybrid rice, and its ability to yield with a bit later planting date.
With that in mind I am looking forward to getting in the field and establishing some test plots to evaluate various control/rotational options for volunteer Clearfield rice, both hybrid, conventional and out-crossed red rice plants.
We have reached an agreement with RiceTec and BASF to cooperate on this work. Both companies have expressed significant concern over the future of Clearfield rice and are eager to seek the soundest recommendations we can make for these fields.
Our primary research site for this project will be at Stuttgart at the Rice Research and Extension Center and our field day this year will be on Aug. 12. I invite you to come take a look at this and the other important work going on in rice at Stuttgart.
Our rice weed control research is made possible through a grant from the Arkansas Rice Promotion Board. This specific work is also supported by a grant from BASF and seed from RiceTec and Horizon AG. All this support is greatly appreciated.
e-mail: bscott@uaex.edu
