Drought + Resistance = surge in rootworm numbers and damage

Written by Jonathan Eisenthal

Alarming signs that the corn rootworm is developing resistance to major GMO corn traits, along with the impact of increasing drought stress and booming rootworm populations, adds up to potential trouble for Minnesota corn producers, according to Prof. Ken Ostlie, a University of Minnesota Extension entomologist, based at the St. Paul Campus of U of M.

Now is a critical time, according to Ostlie, for getting a handle on Bt performance in your fields, and assessing corn rootworm populations. 

“Corn rootworms have been emerging over the last ten days to two weeks, with root injury nearing completion” Ostlie said. “The drought may be aggravating this situation in a couple of ways. Corn rootworm survival is better under drought conditions. Insect feeding on the roots will increase moisture stress and its yield impacts. Also, without thunderstorms, the typical lodging that would be a telltale sign of corn rootworm problems may not be happening, so producers need to get out into the field, dig roots and scout for beetles.

Besides looking for beetles on plants, especially on the ear silks, dig up plants, wash the roots and carefully examine for signs that the worms fed there. “Growers should be concerned when root injury is occurring to a node or more of the roots,” said Ostlie. “In these drought conditions, even loss of half a node may lead to yield loss. Time scale wise, the next week will be crucial to assess what is happening.”

Another concern is that high corn rootworm beetle numbers can trim corn silks so severely that pollination fails. Spraying for corn root worm beetles to prevent ‘silk clipping’ is warranted only on the leading edge of pollination when scouting uncovers the presence of eight-to-ten or more beetles per ear that are keeping silks chewed to within ½” of the ear tip. Minnesota Corn Research & Promotion Council sponsored a radio interview with Ostlie that aired recently on the Linder Farm Network to alert growers to this threat.

For the past six years, with critical funding from the Minnesota Corn Research & Promotion Council, Ostlie has investigated the potential for corn rootworm to become resistant to the main genetic traits used to combat it– genes taken from the bacterium Bacillus thuringiensis and spliced directly into the genetic make-up of “Bt” corn varieties. These Bt genes produce a protein in the plant which is toxic to the rootworm alone. In order to assure that the protein remained effective, producers have planted refuges of conventional corn where the insects could feed. Difficulties in maintaining refuges may have led, in part, to the current resistance, Ostlie said.

“It’s important for farmers to know how the traits are working in their fields,” Ostlie noted. “Scouting how these traits are working in their fields right now will be critical to making good decisions for next year. Producers are beginning to plan what additional root protection measures to take, which seed varieties and pest management resources to purchase for the 2013 growing season.”

Since 2009, Ostlie has tracked a growing resistance problem in Yieldgard VT Triple and Triple Pro, but it may be only a matter of time before resistance impacts other Bt varieties like Herculex Xtra, AgriSure 3000GT or even SmartStax.

“We suggest the fields most at risk are going to be corn planted after corn with a multiple-year history of the same trait,” Ostlie advised. “Those especially would be the ones growers should check–number one looking for signs of excessive moisture stress, number two looking to see if corn rootworm beetles are especially prevalent in a field, and third, digging up plants and washing roots off to see if they had been attacked by the worms.”

Ostlie is working with pest management scientist Bruce Potter, at the Southwest Research and Outreach Center in Lamberton, to develop maps and other information to help growers assess potential rootworm activity in their regions.  We’re particularly interested in reports of performance problems with Bt rootworm traits, Potter says.

Go to this web page to get additional information, or to report Bt hybrid performance problems:  http://www.extension.umn.edu/cornrootworm/

Corn likes to grow here in Minnesota—even in a year of adverse weather conditions

Written by Jonathan Eisenthal

It’s a combination of climate, soils and farmer know-how—corn likes to grow in Minnesota.

Numbers released last week by the National Agricultural Statistics Service (USDA) offer the final picture for the 2011 crop year in its Crop Production 2011 Summary. These data show there are few places that do corn better than Minnesota.

2011 had all the attributes that keep farmers lying awake at night—a long, wet spring with little real heat until July, storms with high winds afflicting plants before they could even pollinate and finally an early frost. Still and all, Minnesota’s 157 bushels per acre average yield put it in close contention with the top producing states: Iowa (172), Nebraska (Many of these acres are irrigated—160), Ohio (158) and Illinois (157). These compare to the national yield of 147.2 bushels per acre.

Even with all the weather challenges, Minnesota corn producers brought in 1.2 billion bushels of corn in 2011. With strong commodity prices this has brought a welcome shot in the arm as the state and nation still struggle with a sluggish economy.

The most telling data point about how well suited the corn crop is to the growing conditions and agronomic practices on Minnesota farms is plant populations. Using random scientific sampling, NASS-USDA looks at places in 10 of the top corn producing states and estimates average plant populations per acre. The 29,350 corn plants per acre in Minnesota is topped by only two states–30,050 plants per acre in Iowa and 29,600 in Illinois. Minnesota even beats Nebraska’s irrigated acres, hands down, where they raise 26,800 plants per acre.

Other important dimensions of this year’s corn crop in Minnesota: Minnesota farmers planted 8.1 million acres of corn and harvested 7.7 million of those acres. Corn represented 41 percent of the state’s planted crop acres and just under 40 percent of all harvested acres last year. By area, Minnesota corn acres represented 9 percent of the nation’s crop. By volume, Minnesota’s 1.2 billion bushels represents 9.7 percent of total corn production for last year in the United States.

Here is the NASS-USDA summary of 2011 corn production nationwide:

Corn for grain production is estimated at 12.4 billion bushels, up slightly from the November 1 forecast but 1 percent below 2010. The average yield in the United States for 2011 is estimated at 147.2 bushels per acre. This is up 0.5 bushel from the November forecast but 5.6 bushels below the 2010 average yield of 152.8 bushels. Area harvested for grain is estimated at 84.0 million acres, up slightly from the November forecast and up 3 percent from 2010.