That fear is largely the impetus behind new management research by Norsworthy and colleagues. “We want to know what to do to minimize the risk of resistance evolving in our current rice production systems. What can we do with our chemical strategies and non-chemical strategies to reduce that risk of resistance? What’s the value of crop rotation versus going with continuous rice? What is the value of flooding at four- to five-leaf rice rather than at five- or six-leaf rice?

“What impact does it have if you make your pre-flood application and it takes seven days to get water across the field compared to two days? What does that mean for selection for herbicide resistance in barnyardgrass?

“What about keeping fields flooded during winter months versus not flooding? Does that have any impact on loss of seed from the soil seed bank and risk of developing resistance?”

The researchers are also looking at planting dates. What about moving planting dates up versus waiting until later?

“We did some computer modeling work with Palmer amaranth. If you look at the current herbicide recommendations for Palmer amaranth, especially in cotton, to a large extent they came out of that modeling work.”

More on that modeling here and here.

When Norsworthy and fellow weed scientist Ken Smith (now working in Texas for Cheminova) first sat down and looked at Palmer amaranth, “we had the idea that we needed to load up the weed control system on the back end. In other words, we thought the plants that were escaping at lay-by in cotton were contributing most to resistance.”

In reality, the duo found that “a very, very strong residual herbicide needed to be down at planting. And we needed to overlay those residual herbicides throughout the season to be successful.

“So, we want to take that same model structure and move it over to barnyardgrass. We’re doing a tremendous amount of data collection; a lot goes into the model: the emergence pattern of barnyardgrass, how many seed are being produced from escapes – 20 or 30 factors.”

The effort has expanded beyond Arkansas borders. Norsworthy is now also working with weed scientists Daniel Stephenson  and Jason Bond in Louisiana and Mississippi, respectively.

“This really goes beyond rice if we’re talking the Mid-South. My goal, in the next year or two, is for us to put together something similar to the ‘Pigposium’ (a very successful pigweed-specific meeting held in 2011) but highlighting barnyardgrass. This is the Number One grass weed we deal with in cotton and soybean.”

Norsworthy wants to provide growers with barnyardgrass solutions as quickly as possible but he says the research is rather open-ended.

“When can you say you have all the answers? Various funding sources have supported the research. The Rice Promotion Board has been very generous, especially around resistance management. The Southern IPM has recently funded a two-year project looking at non-chemical approaches to resistance management.

“But we want to get this modeling done. The idea is that it will help us prioritize and show us to what extent each practice is having an impact on resistance. And when you integrate several practices, to what extent does that reduce the risk of resistance?”


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