Clemson University Corn, Soybean and Small Grain Specialist David Gunter says Holcus leaf spot has shown up in more than a few places in South Carolina corn this year.
Though it has created concern among growers in the state, Gunter says there is no evidence the disease causes any yield loss.
At first glance, the South Carolina specialist says this bacterial disease looks like the kind of damage expected when a neighbor has been burning down with paraquat on a windy day.
Small yellow spots have shown up on leaves in corn fields in several areas of the state, Gunter says.
Holcus leaf spot is rarely found in South Carolina. “There doesn’t seem to be any rhyme or reason to it, but we have been told this problem is only cosmetic and won’t harm yield,” Gunter says.
He stresses that a fungicide spray will not do any good on Halcus leaf spot, or other bacterial diseases.
On the other hand, a disease like northern corn leaf blight, which can develop in cool, high moisture conditions that have been prevalent recently in South Carolina, can be managed with a fungicide if an application is warranted.
Holcus leaf spot is caused by the bacterium Pseudomonas syringae. Infected plants will have round, discrete lesions that are initially pale yellow to white and then enlarge and turn gray or brown.
Lesions have a water-soaked halo and on certain hybrids, the margin of the lesion may appear brown or purple. Lesions are typically distributed from the center to the tips of leaves. Holcus leaf spot often is confused with symptoms caused by herbicide drift or injury.
Moderate temperatures (mid 70s to mid 80s), rainy conditions and wind tend to create an environment favorable for the disease to develop. The disease is not typically found on corn in the Southeast and has not been shown to significantly hurt plant growth and develop or reduce yields.
Other than the sporadic appearance of Holcus leaf spot, the Clemson specialist says, disease pressure in corn has been light this year and so far uneventful.
Overall, he says the corn crops looks good this year for South Carolina growers. “With the recent rains across the state, this year's corn crop has a lot of potential with the crop approaching, or just past pollination. This growing season has been mostly uneventful unless you count the unseasonal warm winter and spring,” he concludes.