ST. LOUIS, Mo. — A dry June accelerated pressure from glyphosate-resistant weeds in soybean fields in the southern Farm World region. As western Kentucky producers weighed the costs of resistant marestail control, a Rabobank report released June 14 indicated that higher U.S. soybean production costs thanks to glyphosate resistance are here to stay.

“Dry weather has escalated the problem of trying to control resistant marestail,” said Jim Martin, extension weeds specialist at the University of Kentucky (UK) Research and Education Center, Princeton.

Glyphosate/2,4-D burndowns saw reduced action this year because of low moisture. Some producers in western Kentucky, where resistant marestail is emerging, were waiting for moisture before spraying. But speaking last week, Martin said producers needed to deal with marestail.

“If you don’t make a decision to spray now, I can assure you by the time we get (soybean) growth, you will have missed effective marestail control,” he said.

Post-emergent options for resistant marestail, such as FirstRate, Synchrony or Classic, could add $10-$15 per acre in production costs for western Kentucky growers. Despite hot and dry conditions oiling yield anxieties, the investment can easily be warranted.

“If you prevent a one-bushel decrease in yield, you can pay for the additional cost,” said Greg Halich, UK extension economist.

No matter what strategies are adopted to combat glyphosate resistance, higher soybean production costs are here to stay. That was the message of Nature Finds a Way: The Rising Cost of Herbicide Resistant Weeds in the U.S, a study released by Rabobank on June 14.

“The development of herbicide-resistant weeds increases costs of soybean production $10 to $45 per acre, depending on the level of infestation,” said Sterling Liddell, vice president of the Rabobank Food & Agribusiness Research and Advisory (FAR) group.

FAR estimates the sustained impact on soybean production costs to be $10-$15 per acre in the northern Corn Belt. Estimated cost increases are higher for Indiana and Ohio, where soybean-after-soybean production is more widespread.

In central and southern Illinois, as well as the northern half of Missouri, costs of controlling resistant weeds are estimated at $30 more than a glyphosate program. The highest cost increases, up to $45 more per acre, are estimated for soybean producers from Tennessee.

Western Kentucky producers were somewhat buffered until this season from the rapid increase in resistant weeds: waterhemp and marestail to the north and Palmer amaranth to the south. Taking lessons about resistance from this dry June will be valuable for next season.

“Getting a better burndown, being better with application, is more essential,” said Martin. “More growers are doing a better job at applying products, and more are looking at residuals.” Pre-emergent residuals are considered crucial in a soybean spray program combating resistant weeds.

In the longer term, stated the Rabobank report, higher costs will require producers to evaluate multiple factors, including changes in commodity prices, seed and precision technology. Even mechanical cultivation options will take on new importance in some areas, but glyphosate will remain an important tool in the soybean growers weed management plan.

Growers may also be making more decisions based on regional differences and regional weed resistance. “This short-term decision to spray is easy,” said Halich. “But the long-term questions are more complex.”