Bruce Schultz, Dunand, Richard T. | 4/19/2005 10:29:10 PM
Farmers who drill-seed rice and want to decrease the time needed to establish a permanent flood may want to consider gibberellic acid to make young rice plants get tall enough, an LSU AgCenter scientist has determined.
The product can be applied with postemergence herbicides, according to Dr. Richard Dunand, plant physiologist with the LSU AgCenter’s Rice Research Station near Crowley.
Gibberellic acid works by elongating plant cell walls that are growing, Dunand said. It is a plant growth regulator found naturally in plants, but introducing additional amounts will enhance growth for roughly three weeks, he added.
As for the benefits to rice producers, establishing a flood sooner allows for improved crop management, Dunand explained, and that could lead to earlier maturity and increased yield.
"The sooner you can get a flood on a rice crop, in general, the better the weed control and the sooner it is going to mature," he said.
Dunand began the work in 1987 – about the same time he started studying use of gibberellic acid as a seed treatment, and his research on that application also is continuing. The efforts are funded by the Louisiana Rice Research Board.
Gibberellic acid also is used to enlarge Thompson seedless grapes, and applications are recommended for citrus and other types of fruits, along with vegetables, Bermuda grass and mint.
Dunand uses the same types of rice plants he’s using in his seed treatment study for the foliar application research.
In the current study, 10 established rice varieties are being tested, along with seven experimental lines.
In that study, a strip of rice plants in the 3- to 4-leaf stage are not sprayed with gibberellic acid but are sprayed with the postemergence herbicide propanil.
Two other swaths of plants are sprayed with propanil and either of two different brands of gibberellic acid – one GibGro by Nufarm America and the other RyzUp by Valent BioSciences.
The cost is low. For example, RyzUp sells for $2.18 per fluid ounce, and it would be applied at a rate of a half ounce to 1 ounce per acre, according to Dunand.
He said all rice varieties are showing similar responses to foliar treatment with either brand of gibberellic acid.
Typically, plants that received gibberellic acid show a height increase of 3-5 inches in five to seven days, the LSU AgCenter researcher said, adding that plants sprayed with gibberellic acid are a lighter-colored green, since they contain no additional chlorophyll in the elongated leaves. The effect on coloration lasts about three weeks.
The smaller plants that didn’t get gibberellic acid have the same amount of chlorophyll, and they have a darker shade of green.
Although foliar applications of gibberellic acid can expedite the establishment of a permanent flood in a rice field, Dunand points out that there is no guarantee plant maturity will be expedited or that yields will be increased.
"It just puts that field in the position to have maximum productivity," he said.
As soon as a field is flooded, any chance of drought stress on the plants is removed. A flooded field also creates a thermal blanket over the plants, with the water holding the day’s heat through the night, he said.
On the other hand, short seedlings submerged with a flood are stressed – and that can affect productivity, he said.
Even precision-leveled fields have low areas, called potholes, where rice often will be submerged when a farmer floods a field, Dunand said, and if a farmer tries to avoid submerging plants in the potholes, the flood on the rest of the field will be too shallow or nonexistent.
"Prolonging the process of establishing the permanent flood across a field in this manner can lead to weed and nitrogen management problems in those areas where establishing the permanent flood depth has been delayed by potholes," Dunand said.
With gibberellic acid, he said, "At least the plants in the potholes are tall enough to allow the permanent flood to be established uniformly across the entire field without regard to the rice in the potholes."
Farmer Jim Hundley said he sprayed foliar applications of gibberellic acid for several growing seasons. And it allowed him to flood fields earlier, he said.
Hundley said spraying by airplane results in considerable overlapping problems, so he preferred a ground-spraying rig.
But Hundley stopped using it two years ago because of the extra cost that couldn’t be justified with the low price for rice.
"When prices went to hell, it was something you surely didn’t have to have," Hundley said. "Once you learn to live without it, you’ve learned to live without it."
Dunand said that sometimes the benefits from research are not always immediate.
"One of the traits of a scientist is patience," he said. "Things don’t always happen over- night. Also, as a research station scientist, you are challenged with not only addressing immediate problems at the farm level, but also with looking into the future and trying to get answers to problems that you think lay beyond the horizon."
He said it’s likely the benefits of gibberellic acid will continue to expand.
"For one, I think that as farmers begin to explore the possibility of lowering seeding rates, it will be noted that the plants are shorter than when grown at higher seeding rates," Dunand said. "Inter-plant competition with high stands causes plants to elongate more than at low plant populations. This slower accumulation of height will lead to later flooding and a foliar application of gibberellic acid will easily make up the difference."
Dunand also has done research on the use of gibberellic acid in later stages of a rice crop to get better panicle extension after farmers complained that too much leaf material of some semi-dwarf varieties was ending up in their harvesting machinery. But rice breeders at the Rice Research Station made improvements that solved that problem.
Based on some of his observations, Dunand said he noted some things about panicle development that warranted further investigation. As a result, he’s working on a study to find out if gibberellic acid applied later in the growing season can increase yield, but he’s guarded about revealing too much at this point.
"We’re in the experimental stages with that, and we’ve had some promising results," he said, explaining that so far yield increases have not been consistent from year to year.