No. 5 Pest Picture Intensifies in 2015
By Emily Unglesbee
DTN Staff Reporter
Let’s face it, American farmers grow some mighty desirable crops.
Each season, growers compete with thousands of species of insects, fungi, nematodes and weeds. This year, the odds tipped in the pests’ favor.
The 2015 season served up two new corn diseases, a newly identified soybean disease, and one aggressive new caterpillar pest. In the meantime, weeds continued to outpace available technology. Two long-awaited herbicide-tolerant crops remained in regulatory limbo as weed resistance to products on the market continued to expand.
Glyphosate resistance remains a top concern for producers across the country. Dense resistant waterhemp populations sent some Midwestern growers back to weeding by hand in 2015, and marestail had a field day in fields left fallow from flooding.
Those high water issues set back Palmer amaranth in some parts of the Midwest, but down South, grass weeds gained momentum, said University of Tennessee weed scientist Larry Steckel. Populations of ryegrass, Johnsongrass, and goosegrass with tolerance to glyphosate are becoming increasingly difficult to control, particularly in post-emergence situations.
“Not all glyphosate-resistant weeds are created equal, however,” Steckel said. “Palmer amaranth remains the driver weed.” This king of weeds dealt growers another blow after populations with resistance to PPO-herbicides were confirmed in Arkansas and Tennessee this year. PPO-inhibitors such as Flexstar, Cobra and Valor have been a staple of broadleaf control in rice and soybeans, particularly since the advent of glyphosate-resistance. Losing those PPO options will hurt, Steckel noted. “In 2015, we took a big step back on the management of Palmer pigweed; we have a lot of fields that look like they did in 2011,” he said.
The weeds are moving faster than new technology can get to the field. Monsanto’s Roundup Ready 2 Xtend traits, which tolerate glyphosate and dicamba, still await global import approvals and need EPA approval of the complementary herbicide. Monsanto launched the Xtend trait system over a limited number of cotton acres in 2015, but there was no herbicide approved for use.
Dow AgroSciences’ Enlist Weed Control system, a trait program designed to tolerate a proprietary pre-mix of 2,4-D Choline and glyphosate, also needs critical China approvals before it can be commercially launched. That system was dealt a further blow this fall when EPA petitioned a federal court to withdraw registration of herbicide premix for further review.
In the meantime, growers are spending more money on weed control than ever before. “A lot of growers’ costs have gone up 200% to 250%,” Steckel estimated. “And that doesn’t even count a lot of the folks hired to go out and hand weed.”
Heavy and persistent rainfall across the Midwest and South in the spring and early summer gave crop diseases a chance to thrive in soybean and corn fields. Familiar old standbys — northern corn leaf blight and gray leaf spot in corn and sudden death syndrome and white mold in soybean — showed up. Meanwhile, new diseases also joined the fray.
Mississippi State researchers have discovered a new soybean disease they’re calling soybean taproot decline. MSU scientists are testing and studying the fungus, which they believe may have been confused with sudden death syndrome in the past.
Tar spot, a fungal disease native to Central America and Mexico, was identified in Indiana and Illinois in September. Shortly after, bacterial leaf stripe, which hasn’t been spotted in the U.S. since the ’70s, cropped up in Illinois corn fields.
Tar spot isn’t a significant yield robber in its home countries near the equator, and bacterial leaf stripe had no economic impact on corn crops in the past. But scientists are urging growers to be on the lookout for both in 2016.
In July, an aggressive global agricultural pest known as the Old World Bollworm landed on U.S. shores for the first time. Three moths were found in Manatee County, Florida — a small discovery with big implications for American farmers.
Known officially as Helicoverpa armigera, the Old World Bollworm caterpillar causes enormous global agricultural damage each year to vegetables, cotton, soybean, corn and many other grain crops. It has a history of developing resistance to insecticides and some Bt proteins, and nearly a third of all global pesticide applications are aimed at killing it in China, India, Australia, Africa and Europe.
USDA’s Animal and Plant Health Inspection Service has launched multi-state surveys to see if the bollworm has made it beyond Florida.
In the meantime, eradication is unlikely, so American growers will have to learn to live with this new pest once it is established, said Louisiana State University entomologist David Kerns. “I would be surprised if we could contain it,” he said. “It could hybridize with our native bollworm, and we have no idea what that hybrid will be like. There are a lot of unknowns with this pest. I think the next couple seasons will tell us a lot.”
Emily Unglesbee can be reached at emily.unglesbee@dtn.com.
Follow Emily Unglesbee on Twitter @Emily_Unglesbee.
