Spraying to control foliar diseases typically not recommended in the fall

Friday, November 11, 2016

Mild and relatively dry conditions throughout most of Oklahoma in recent months should make fall foliar diseases relatively uncommon, though some areas have received sufficient rain or had dew points to favor development of wheat diseases.

As always, producers need to be vigilant but it is also important to know and employ research-proven best management practices, cautions Bob Hunger, Oklahoma State University Cooperative Extension wheat pathologist.

“I am not a proponent of spraying in the fall to control foliar diseases such as leaf rust because leaf rust development slows and stops once Oklahoma begins to regularly experience temperatures of less than 60 degrees Fahrenheit,” he said.

Typically the lower/older leaves with leaf rust pustules die but the youngest leaves are green and healthy. Furthermore, grazing helps to remove leaf rust infection, is not harmful to cattle and also “opens” the canopy so there is increased air circulation and drying, which are less favorable to development of leaf rust.

“Given these considerations, spraying to control leaf rust in the fall generally is not necessary, especially for wheat producers using a dual-purpose grazing/harvesting management system,” Hunger said.

The primary concern with fall leaf rust is that – with a mild winter and sufficient moisture – the rust will survive through the winter and inoculum will be present in fields to start the disease early in the spring.

“Monitoring fields now and through the late winter into early next spring is recommended to know if you have leaf rust and other foliar fungal diseases present in your field,” said David Marburger, OSU Cooperative Extension small grains specialist. “Also, it is important to know the susceptibility of your wheat variety to the leaf rust fungus and other fungi.”

Marburger said wheat growers armed with these two pieces of information, as well as paying attention to the weather forecast in late winter to early spring, will help promote sound decisions regarding whether or not a fungicide application will be needed to control rust and other foliar fungal diseases in the early spring.

In addition, some samples that recently have come to OSU’s Division of Agricultural Sciences and Natural Resources for diagnosis appear to be related to abiotic conditions such as dryness or low fertility.

“Some leaf spots have been observed on these samples but they are either secondary or of low incidence and not a cause of major concern,” Hunger said.

For all the foliar wheat diseases – leaf rust, stripe rust, powdery mildew, tan spot and Septoria leaf blotch – control in the spring is more critical than control in the fall.

“I have heard of growers adding a shot of fungicide with a fall herbicide application to limit disease present but I have no data to support the value of such an application,” Hunger said. “It is possible there may be some value to it because plants are smaller and not growing as actively. Thus, limiting the amount of foliage loss due to a disease such as tan spot will contribute to the overall health of the wheat going into winter.”

Additional information about the control of foliar diseases in wheat is available online at http://osufacts.okstate.edu by accessing OSU Extension fact sheets EPP-7661, “Major Foliar Fungal Diseases of Wheat in Oklahoma,” and CR-7668, “Foliar Fungicides and Wheat Production in Oklahoma – March 2016.”