Leafhopper & other sap feeding insects – Adult and nymph grape leafhoppers feed on sap in leaf cells, leaving pale stippling marks on leaves. Severe feeding will cause leaves to turn from yellow to brown. More importantly, many of leafhoppers can transmit disease pathogens. Some examples are: glassy wing sharpshooter (Homalodisca vitripennis) that is one of vectors of Pierce’s disease; and Scaphoideus titanus that is one of vectors of grapevine yellows.
Early Black Rot infection presents itself as small-discolored lesions on leaves. Lesions turn brown and expand in time. Black fungal bodies called pycnidia develop in the lesion in a concentric pattern, which is visible to the naked eye.
Hail damage may cause shot holes and ripping of leaves, scarring on shoots as well as bruised and cracked fruit. Hail damage can easily reduce crop yield and quality through physical damage and by making fruit vulnerable to secondary infection.
Mites-European red mites, Panonychus ulmi, cause’s chlorosis and bronzing, by piercing and feeding on leaf epidermis. Two spotted spider mite feed on the underside of leaves, cause yellow stippling on the top side of leaves.