Symptoms vary by host. See CPHST pest datasheet for a complete list of hosts and the associated symptoms.
In grape: Typical symptoms comprise discoloration of leaves including the veins, often associated with downcurling of the leaf blade, lack of or incomplete lignification of shoots that later turn black, abortion of fruit clusters or shriveling of the ripening fruit. In most cultivars, the symptoms of bois noir remain restricted to parts of the infected vines for several years. Bois noir usually does not kill the infected vines, although their vigor can be significantly reduced. In red grape cultivars, leaf reddening occurs. In white cultivars, yellow, necrotic veins occur. Shriveled grape clusters occur in both red and white grape cultivars.
In corn: Symptoms include midrib, leaf, and stalk reddening, followed by desiccation of the entire plant, abnormal ear development, and incomplete kernel set. Maize redness (MR) may cause economic losses. Environmental factors play a role in both the intensity and incidence of MR, with more severe disease being associated with early-planted fields and hot, dry summers.
In potato: Symptoms in potato include reddening and upward rolling of leaflets, reduced size of leaves, shortened internodes, and aerial tuber formation. Plants grown from infected tubers give rise to normal or spindly sprouts (hair-sprouting). Where normal sprouts arise, symptoms are first apparent about 60 to 80 days after sowing, as a yellowing and rolling of the leaves. This is followed by production of aerial stolons and tubers in different parts of the stems close to the axils.
In tomato: Leaves that develop before infection become greenish-yellow, especially at the margins, which may roll upward. Newly formed leaves become more yellow and are smaller. Stems become thin at the apex as growth ceases, but stems enlarge at infection sites as a result of abnormal phloem formation. This abnormal phloem appears as a greenish, water-soaked band 1 to 2mm wide, which extends towards the xylem. Lateral shoots develop, giving the plant a bushy aspect. Flower buds assume an abnormally erect position; the sepals, whose veins develop a violet color, remain completely joined and the calyx is enlarged and cyst-like ("big bud").
Flowers, if already formed when infection occurs, become similarly erect and may be sterile, and petals are greenish instead of yellow. Flower distortion is common, and petals of young flowers become totally dwarfed and green (virescent). Peduncles are thicker than normal. Fruit development is arrested following infection. Green fruits already formed become solid, dry and ripen very slowly. Necrosis occurs at the embryonic center in younger fruits. Pedicels of fruits are thicker than in healthy plants, in spite of the relatively small fruit size.