Linda Benedict, Purvis, Myra, Padgett, Guy B., Hollier, Clayton A., Mascagni, Jr., Henry J. | 9/1/2009 8:26:21 PM
Boyd Padgett, Clayton Hollier, Rick Mascagni and Myra Purvis
Fungicides are used to manage diseases in many field crops grown in Louisiana. Until recently, this practice has not been evaluated on corn produced in the state. In the past, foliar-applied fungicides have not been promoted in corn because diseases either do not develop or develop late in the season having minimal or no impact on yield. However, with advent of newer fungicides, some sectors of the agricultural chemical industry are promoting these applications, even in the absence of disease, to increase yields and preserve stalk density to prevent lodging – the tendency of stalks to fall over.
It was uncertain if this practice would consistently benefit Louisiana corn producers because research addressing this is limited in the state. Therefore, in collaboration with industry, LSU Ag Center scientists initiated research in the spring of 2007 to determine the feasibility of this practice. The objectives of this research are to determine if selected fungicides are effective for managing diseases affecting corn in Louisiana; if yields are higher in fungicide-treated corn than in untreated corn; and if stalk density in fungicide-treated corn is greater than in untreated corn.
Field tests were conducted during 2007 and 2008 on several AgCenter research stations and in producer fields. Test sites included the Macon Ridge Research Station near Winnsboro, the Dean Lee Research Station near Alexandria and the Northeast Research Station near St. Joseph. With the assistance of county agents, tests were conducted in producer fields in Avoyelles, Concordia, East Baton Rouge, Franklin, Morehouse, Tensas, Rapides, Richland and St. Landry parishes.
In 2007 and 2008, tests were conducted at the Macon Ridge and Northeast research stations to evaluate Quilt and Headline fungicides for their effect on corn diseases, stalk density and grain yield and quality. Evaluations in 2007 included eight hybrids at the Macon Ridge Research Station and six hybrids at the Northeast Research Station. A single fungicide application was made to each variety while in the tasseling growth stage and compared with the same variety without treatment. During the growing season, plants were monitored periodically and rated for disease incidence and severity. Stalk density was assessed when corn reached physiological maturity. This was determined by collecting stalks from each plot and recording fresh and dry weights, as well as the diameters for each stalk. Densities were then calculated using this information. Yield and test weights were also recorded.
In both years, diseases either did not develop or developed late in the growing season. Therefore, the effect on disease was not evaluated.
In 2007, the effects on stalk density and yields varied within and among hybrids (Tables 1 and 2). At the Macon Ridge location, yield differences between the Quilt treatment and no treatment ranged from 15.7 bushels per acre to minus 14.3 bushels per acre, and treated hybrids averaged 4.6 bushels per acre less. Yield differences between the Headline treatment and no treatment ranged from 33.9 bushels per acre to minus 19.7 bushels per acre, and yields averaged 6.33 bushels per acre more when Headline was used.
Results from the test at the Northeast Research Station in 2008 were similar to those in 2007. Yield differences were from 11.4 bushels more per acre to 4.3 bushels fewer per acre between Headline-treated hybrids and nontreated hybrids (Table 3). When averaged across hybrids, corn treated with Headline yielded 2.3 bushels per acre more than nontreated hybrids. There were no significant differences between stalk densities and test weight among most hybrids.
During 2007, Headline, Quilt, Quadris and Stratego were evaluated in tests at the Dean Lee Research Station and at off-station sites. Tests with producers usually consisted of large areas in fields either treated with a fungicide or not treated. A total of 21 corn hybrids were evaluated in these tests. Applications were made to corn at or near tasseling. Disease epidemics did not develop to appreciable levels in most tests. Where diseases were observed, however, incidence and severity were lowest in fungicide- treated corn. When averaged across tests and compared to plants not treated, yields were 0.89 bushels per acre higher with Headline applications, 0.06 bushels per acre higher with Quilt and 2.38 bushels per acre higher with Quadris (Table 4). Corn treated with Stratego averaged 1.35 bushels per acre less than corn not treated.
Even though yield response was minimal or nonexistent, responses by individual hybrids varied considerably. Yield differences between fungicidetreated hybrids and untreated hybrids ranged from +12 bushels per acre to -20.4 bushels per acre for Headline, +14.9 bushels per acre to -17.2 for Quilt, +9.0 bushels per acre to -5.3 bushels per acre for Quadris and +10.7 bushels per acre to -27.7 bushels per acre for Stratego.
Because disease epidemics did not develop to significant levels in most tests, the effect of fungicides on disease development is inconclusive. In LSU Ag Center tests, fungicides did not preserve stalk densities or increase test weights in most hybrids. The effect of fungicides on yield was not consistent between hybrids or across years.
When compared with untreated corn, yields were 6 bushels per acre or higher in 33 percent of the tests with Headline or Quadris, 27 percent of the tests with Quilt and 50 percent of the tests with Stratego when compared to untreated corn. These inconsistent responses do not support the practice of automatically applying fungicides to corn. In hybrids where disease epidemics develop to damaging levels, the probability of an economic return from a fungicide application may increase.
The LSU AgCenter will continue to conduct research in this area to further evaluate the efficacy of fungicide applications to corn.
Boyd Padgett, Professor, Macon Ridge Research Station; Clayton Hollier, Professor, Department of Plant Pathology & Crop Physiology, LSU AgCenter, Baton Rouge, La.; Rick Mascagni, Professor, Northeast Research Station, St. Joseph, La.; Myra Purvis, Research Associate, Macon Ridge Research Station, Winnsboro, La.
(This article was published in the summer 2009 issue of Louisiana Agriculture.)