“Phosphite provides an alternative chemistry for growers to consider. This is particularly useful because the scab fungus has developed resistance to some fungicides currently used for control.”

Bock and his colleagues also studied whether fungicides applied from ground-based sprayers are providing adequate scab control in mature pecan trees, which can be 60 to 80 feet tall.

They determined that, in pecan trees that did not receive fungicide, the disease was most severe in the lower canopy and least severe at the top of the tree. But in trees that did receive fungicide, disease was reduced only up to a height of 40 feet; above that, there appeared to be no effect of fungicide on disease severity, compared to the non-treated trees.

“There was a consistent reduction in scab severity on foliage and on immature fruit through August due to fungicide treatments below 40 feet,” says Bock.

“Where tall pecan trees preclude effective ground-based spray coverage, aerial application might be an option to reduce the severity of scab in the upper canopy. The efficacy of this option is currently being investigated.”

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