How to Manage Pests
UC Pest Management Guidelines
Botrytis blossom and shoot blight occurs in early spring and fruit blight later in spring. The first symptom to be observed is wilting of tender shoots; later leaves shrivel and dry. Young shoots die and the leaves remain attached, a symptom called flagging.
Blossom blight is more severe in male than female trees, especially in the 02-16 and 02-18 male selections. The fungus enters the flower and invades the wood where it causes cankers on current or two-year-old shoots. Cankers can coalesce and measure up to 10 inches (25 cm) long. When cool, wet weather prevails, diseased blossoms and basal portions of shoots are generally covered by buff-colored massed of spores. Large circular lesions can develop on blades of both female and male trees, and portions of the leaf blade (usually a V-shaped area near the terminal) mainly on male trees may also be infected and killed by the fungus. Late rains can result in infections of fruit clusters, killing parts or the entire cluster, which become beige in color.
Infections occur in spring on succulent current-season growth. Most Botrytis cankers occur at the base of shoots and most likely start from contaminated buds and bud scales. The fungus colonizes the bud scales and then grows and infects the developing shoot. Shoots wilt and form a shepherd's crook. Inflorescences, especially in male trees, are also attacked.
Blighted shoots provide inoculum during the current growing season and in the following spring. Under humid conditions, the fungus colonizes and sporulates on male flowers that are on the tree or already dropped to the ground. Other sources of inoculum include infected weeds, leaves, and immature fruit dropped to the ground, or other crops neighboring the pistachio orchard. The disease is prevalent during cool, wet springs and causes damage by killing current season shoots and fruit, thus reducing fruiting wood for the following season and yields (fruit blight phase).
Orchard sanitation may help reduce the incidence of Botrytis blight. By pruning blighted shoots and removing them from the orchard the level of inoculum in the orchard may be reduced. Also, by pruning the blighted shoots and shoots with cankers, the potential for invasion of the tree by Botryosphaeria dothidea is reduced.
If spring weather is cool and wet during bloom, consider treating for this disease.
UC IPM Pest Management Guidelines: