Limited irrigation water for some California pistachio growers in the San Joaquin Valley could reduce the threat of Alternaria blight this year by reducing growth and density of the canopy.

A sparser canopy could lower humidity levels within the orchard and lessen the risk of Alternaria, says Bob Beede, Kings County University of California Cooperative Extension Farm Advisor.

“Pistachio growers realize that the drier conditions on the west side of the San Joaquin Valley create less potential for Alterneria than on the eastern side where the Sierras and poor infiltration increase relative humidity,” he says.

“High relative humidity from standing water associated with poor infiltration or excessive irrigation promotes Alternaria infections in July and August. This can lead to lower nut quality, principally due to shell staining.”