Foliar diseases in sorghum are primarily a problem in the United States—in the Delta, southeast and Mid-Atlantic states—where humid and rainy weather favor their proliferation.
Of these diseases, anthracnose is easily the most widespread and troublesome. Hybrids differ in their tolerance to anthracnose. Growers in those regions where anthracnose is an annual problem should make it a priority to plant a hybrid with good tolerance.
When anthracnose is present in the field, fungicide application may be considered. An excellent trial examining the effectiveness of fungicides was conducted by Virginia Tech and North Carolina State at eight locations over a three-year period. Five fungicides were compared and applied at different growth stages.
Anthracnose severity and onset of the disease varied with location. One of the findings of the study was that the onset of the disease in the field had a larger impact on yield than disease severity at the end of the season. Economic return was improved at six of the eight sites when a fungicide was applied. It was also determined that fungicides were only effective when the onset of anthracnose occurred before flowering and humid wet weather prevailed.
Of the five fungicides tested, Headline (pyraclostrobin) and Priaxor (pyraclostrobin + fluxapyroxad) provided the best anthracnose control followed by Quadris (azoxystrobin).
In summary, foliar fungicides should only be applied to sorghum when the onset of foliar disease occurs before flowering and wet, humid weather is anticipated that will cause the disease to flourish. Fungicide should be applied between the boot and early flowering stages.
Foliar fungicides are often used in other crops to promote overall health even in the absence of disease. However, in sorghum studies yield has seldom been enhanced and it is almost never economical. In 25 trials conducted from 2008 to 2017 in Texas, Kansas, Nebraska and South Carolina, only four trials had a significant yield response to fungicide. Of these four, significant foliar disease was present in three of the trials.
In addition, only two had a positive economic return from fungicide application. In many of the 25 trials, researchers reported greener and healthier looking plants, but this did not translate into higher yield.
Editor’s note: Brent Bean, Ph.D., Sorghum Checkoff Director of Agronomy, Lubbock, Texas. For more information visit www.sorghumcheckoff.
