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Conditions prime for leaf spot in Bermuda grass

published: October 6th 2017
OVERTON – Humid conditions and excess forage in East Texas have created a prime environment for leaf spot in Bermuda grass hay fields, according to a Texas A&M AgriLife Extension Service expert.
Dr. Vanessa Corriher-Olson, AgriLife Extension forage specialist, Overton, said a high volume of forage growth this year and weather conditions in East Texas have created conditions for Helminthospor-ium leaf spot, or Bipolaris, a plant fungus, to infest Bermuda grass fields.
Conditions for leaf spot are extreme this year because rain events have created prime conditions for the fungus and prevented many producers from accessing hay pastures to cut, she said. The excess forage that keeps moisture within the canopy and prevents sunshine and air movement creates optimal conditions for an infestation.
Leaf spot typically appears in late summer when weather is warm, usually between 75 degrees and 90 degrees, with high relative humidity, she said.
“It typically affects our Bermuda grass pastures and hay meadows when there is excess forage and conditions that support moisture and heat,” Corriher-Olson said. “So in a year like this one where we’ve had moisture throughout and forage production is high, the possibility of leaf spot infestations is higher, especially in fields that are not grazed or harvested in a timely manner.”
Infestations occur in irregular patches, but severely affected hay fields may become brown and thin, she said. Heavy infestations can decrease hay yields and quality.
Leaf spot can be identified as lesions on leaves that are brownish green to black in color, she said.
The only defense against leaf spot is avoidance, Corriher-Olson said.
Selecting resistant varieties of Bermuda grass, maintaining soil fertility, removing thatch from pastures and harvesting forage in a timely manner will reduce the risk of infestation, she said.
“There are no fungicides that are legal, affordable or effective against leaf spot,” she said.
Corriher-Olson said selecting resistant varieties, such as Tifton 85, Tifton 44 and Coastal Bermuda grass, will not guarantee disease infestations will not occur if conditions are extreme but they will perform better than other varieties. Soil fertility, especially maintaining proper potassium levels, can help plants fight disease more effectively.
“Potassium deficiencies can weaken our Bermuda grass, which makes it much more susceptible to diseases,” she said.
Grazing the pasture or cutting grasses to open up the canopy and allow sun and air movement into the thatch to dry the forage is critical to avoiding the fungus, she said.
“All the rain has been good for hay producers because of the excess forage growth, but that can also be a problem if they can’t get into the field to harvest it,” she said. “I’ve noticed pastures that were lodging because producers weren’t able to access them in a timely manner. Lodging creates a high moisture environment that promotes the fungus.”

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