Over the past few years, rice growers have begun moving from traditional flood production to row rice, also known as furrow-irrigated rice. Furrow-irrigated rice growers face different challenges when it comes to weed control in their fields. Once herbicides dissipate in a continuous delayed-flood rice culture, growers depend on flooding to help control weeds. Flooded rice creates the anaerobic conditions that stops the germination of certain weed species hidden in the soil, while furrow-irrigated rice supplies weed species with enough moisture and oxygen to germinate and grow.
Dr. Hunter Bowman, Extension Rice Agronomist at Mississippi State University, spoke to growers attending the 2023 Cotton and Rice Conference held in Baton Rouge, Louisiana, about research on irrigation water management and herbicide application timing in furrow-irrigated rice.
“With traditional levee rice, it takes a lot of labor to pull levees, but it also takes someone you trust to check that water depth daily, maintain proper flood, also be able to plan ahead,” says Bowman.
Furrow-irrigated rice allows for easier crop rotation, decreases labor and reduces water usage, but producers must look at the proper timing of water application and weed control.
“Most of our herbicides in rice were designed to be applied in a flooded system. So, we apply it and then we put a flood on it and the flood maintains weed control throughout the rest of the year,” says Bowman. “When we flush water across the fields every three to four days, we're just flushing that herbicide out of the field.”
Research is being conducted to help answer the question of how often growers need to irrigate row rice based on yield projections. Field trials in 2021 looked at irrigation intervals every day versus every 7 days and during a span of 3 to 5 days. Research showed growers irrigating every day returned the highest yields; every 7 days proved too long and yields were reduced. Irrigating every 3 to 5 days shows a slight decrease in the yields as compared to every day, but the time frame is more realistic for most growers.
Herbicide Timing in Row Rice
Research that looks at the ideal herbicide application window is a bit more complex, considering soil type, weed species and flood schedule. While growers are encouraged to use herbicide solutions that rotate active ingredients and modes of action, Bowman says the timing of flooding can be a third leg to the weed control stool.
“Most of our row rice is going to be grown on clay-type soil. As that clay starts to crack then the weed will emerge through the cracks,” says Bowman. “You've got a herbicide layer at the top that might be an inch or two deep, but that weed will come out through the crack and from under that herbicide layer.”
Researchers are also investigating if herbicides are lost more rapidly than in continuous flooded rice systems. Do growers need to be more aggressive with their herbicide applications?
With that research, growers are looking to create herbicide plans to better control barnyardgrass and Palmer amaranth in furrow-irrigated rice. In these trials, researchers looked at the days between herbicide applications, 7, 14, 21, 28 and 35 days after the rice emerged using two sequential applications. The research found that for barnyardgrass control, anything over a 21-day interval was ineffective, but with Palmer amaranth, 21 days was too far out and the 14-day interval was ideal for weed control.
When looking at moving from traditional flood production to furrow-irrigated rice, growers must understand the challenges of a new production system. Research continues to expand to look at water management and herbicide application timing that will allow growers to better use their resources and optimize yields.
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