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Red rice outcrossing evident in Arkansas study

I want to write one more article on the red rice outcrossing issue and attempt to give you a few more details on the studies that Tomilea Dillon has conducted and I have written about in several articles.

Last year she had 3 red rice control studies at Stuttgart. Since we had the three new Clearfield rice varieties, (CL121, CL141 and the 0051 they dropped for Arkansas), she planted one of these varieties in each study. Her good treatments, like the 4 oz. ppi followed by 4 oz. postemergence, provided 100 percent red rice control. However these were 30 treatment tests and some of the treatments were either check plots or single treatments that provided incomplete control.

In addition, the rice plots were slightly wider that the spray boom (which could represent sprayer streaks in the field if they occur) so there was some red rice between plots. As a result, a lot of red rice went to seed in the test areas even though the recommended treatment plots were clean.

Dave Gealy, a USDA weed scientist located at Stuttgart, discovered in Tomilea's plots last year that the red rice and Clearfield rice in at least two of the studies were flowering at the same time. Therefore these studies represented both things that can go wrong in a farmer's field: A red rice failure for whatever reason and simultaneous flowering of the two types of rice.

This year, Tomilea went back into those original plot areas and worked them up just as she would have to plant rice. In each plot, a solid infestation of volunteer red rice emerged and she made three applications of Newpath (two at a 4 oz. rate and one at an 8 oz. rate) prior to flooding. The plots were then flooded.

She is in the process now of counting surviving plants and characterizing each plant. She had emerged plants numbering from 100 in one test to 700 in another. They are beginning to head so she can confirm the number that are red. However, approximately one third of the surviving plants have red rice foliar characteristics.

Just by luck, the plots are around an acre in size. The 100 to 700 surviving plants are only a scattered infestation. However, it is a sobering number of plants on a per acre basis that appear to be Clearfield tolerant red rice now. Where these individual plants are tillering much more profusely than they would in competition with rice, the amount of seed they will produce will totally infest that acre.

Some have asked, “why are you even doing this, those red rice plants should have been destroyed.” The answer is to study the problem ahead of time. If it happened in her research, it will happen on the farm. We can either study it now or study it after it occurs on the farm. We need to know many things. “Will Roundup control these outcrossed plants in soybeans?” We think so, but nobody knows for sure until we spray them.

Our goal is to learn as much as we can about the potential outcrossing and how to manage it in hopes of preserving the technology for the future. She has proven beyond a doubt that it can occur. In addition while the numbers and percentages sound extremely low, with a couple of wrong management decisions, the problem can occur much more quickly that the numbers would indicate.

From here, I will quit being grouchy and start dealing with how to prevent it.

Wheat planting time is getting here. I am sure one of the primary questions will be on Hoelon-resistant ryegrass. We at the University of Arkansas are devoting a lot of research effort to this problem. All of the research effort is supported by your check-off dollars administered by the Wheat Promotion Board.

First, if a field has a history of resistant ryegrass and you do not have to plant it to wheat this fall, a fall fallow program can be extremely effective.

Based on research by Dick Oliver (a UA weed scientist located at Fayetteville) and a former graduate student conducted near Little Rock, one year of fallow in a severe resistant programs population, resulted in 95 percent control of ryegrass for the next two years the plots were planted back to wheat. This was with no herbicide used in the subsequent wheat crops.

To make the fallow program work, the field not only has to lay fallow, but it has to be tilled and smoothed several times. The key is to get it tilled and smoothed just as you were preparing a seedbed for planting wheat — as soon as possible after soybean (or other summer crop) harvest. This will allow a major ryegrass flush to occur with the first good cool snap.

From there, every time you get a good flush of ryegrass and it is dry enough, destroy that flush with tillage and wait for another. We are going to have to depend on more than herbicides to fight this problem and a fallow program is the most effective thing we have.

If you do have to plant the field to wheat, some other cultural practices can help in the fight. Oliver and the student looked at a recommended versus 2x seeding rates and also an increased fall nitrogen program. Neither made a drastic difference in ryegrass control. However, use a seeding rate that will give you an excellent, uniform stand. Do not over fertilize to the point of getting too much fall growth, but use a recommended fertility program that will give you good fall growth and cover.

Every time I encourage delayed planting, I fear those calls from the guys who delayed and then it turned off wet and they didn't get planted. However, if you can smooth the seedbed and get one good flush of ryegrass up that can be destroyed before planting, it will help tremendously.

They studied conventional versus no-till effects on ryegrass control and it didn't really make any difference. We thought maybe destroying the emerged ryegrass and then not disturbing the seedbed at planting would be a big help. The results didn't show any advantage over conventional tillage.

Some wheat varieties are more aggressive and competitive than others. Ask your county Extension agent to get you some of that information.

I am not attempting to assume the role of wheat agronomist here. However, I can tell you that the best herbicides we are looking at for resistant ryegrass control are only providing 50 to 70 percent control. However, if you combine this with the cultural practice that promotes good stand and growth, the wheat will overpower the ryegrass that is left.

Where we use these principles, we are producing 50 to 70 bu/A wheat in the herbicide plots that have 50 to 70 percent control, versus 20 bu/A or so in the untreated plots.

Ford Baldwin is an Arkansas Extension weed scientist.

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