GARDEN CITY, Kan. — One of the common crop rotations used by farmers on the High Plains — wheat-corn-fallow using Roundup Ready corn has its advantages, but volunteer corn can cut into yields some years, Kansas State University researchers said.

 


GARDEN CITY, Kan. — One of the common crop rotations used by farmers on the High Plains — wheat-corn-fallow using Roundup Ready corn has its advantages, but volunteer corn can cut into yields some years, Kansas State University researchers said.
The results of a three-year study conducted across several locations in western Kansas indicate that in average years, when conditions were neither drier than, nor wetter than usual, volunteer corn growing in fallow negatively impacted the following wheat crop’s tiller production and grain yield, but had minimal effect on grain test weight.
"Producers who grow glyphosate-tolerant corn are challenged with controlling volunteer corn during the fallow period in a dryland wheat-corn-fallow rotation," said John Holman, cropping systems agronomist with K-State Research and Extension. Volunteer corn — those pesky plants that grow from kernels left in the field from previous crop - can germinate throughout the fallow period and are not controlled by traditional herbicides used in chemical fallow. This creates an issue for producers who must allow the volunteer corn to grow or apply a selective grass herbicide, often several times, which in turn increases weed control costs.
K-State researchers started the study in 2007 to determine common levels of volunteer corn in producer fields and to quantify the effect of volunteer corn on soil moisture during the fallow period and the subsequent effect on winter wheat tiller production, and grain yield, protein and test weight.
The three-year study, conducted by Holman in collaboration with K-State agronomists Alan Schlegel and Brian Olson, found that for every200 volunteer corn plants per acre, wheat yield was reduced by one bushel per acre in years with average growing conditions and precipitation. At Tribune, the first bushel of wheat yield was lost when volunteer corn density was 75 plants per acre. However, in years with very low precipitation or very high precipitation, volunteer corn growing during fallow did not impact the subsequent wheat crop’s yield.
University-managed land and several western Kansas producer fields were included in the study.
Over all fields included in the study, including producer and university acreage, fields averaged 500 volunteer corn plants per acre.
"On the basis of the test results in Colby and Tribune from 2008, a density of 500 volunteer corn plants per acre would cut wheat yields by 4.6 bushels per acre," said Holman.
"A selective grass herbicide can be used to control flushes of volunteer corn, but may cost close to $15 per acre," said Troy Dumler, K-State southwest area extension agricultural economist, also a collaborator on the study. "Of course the price of wheat and herbicide will influence the amount that can be spent to control volunteer corn. With wheat at about $5 per bushel, a yield loss of 3 bushels per acre would be needed to justify additional herbicide treatments to control volunteer corn. That would require a density of more than 250 volunteer corn plants per acre."
A few methods to reduce the cost of controlling volunteer corn would be to spot spray the volunteer corn, use a selective grass herbicide in place of glyphosate for sequential herbicide applications in fallow, or use a different herbicide program other than Roundup and a non Roundup-Ready corn variety.
"This study has shown that volunteer corn densities are potentially high enough to reduce the amount of soil moisture stored during the fallow period and subsequently reduce the following winter wheat crop’s yield," Holman said.
More information about the study and other K-State research in western Kansas is available at county and district extension offices and on the Web at http://www.wkarc.org.