Crown-gall or Black Knot (Bacterium tumefaciens). - A tu-merous, gnarled outgrowth on roots and stems, especially on European varieties. Frost injury often forms an infection court for the bacteria. See p. 276.
Control. - Grub out and burn infected vines.
Downy Mildew or Leaf-blight (Plasmopara viticola). - Appears in white frost like patches on under side of leaf, the upper side of the leaf showing a yellowish discoloration ; gradually spreads to all parts of the leaf causing it to dry up. Attacks the berry, which remains hard and white or gray. Worst on hybrids with vinifera blood ; especially common on Delaware and Roger's hybrids. Widespread in North America.
Control. - Spray as for Black-rot. Necrosis or Dead-arm Disease (Fusicoccum viticolum). - Attacks shoots, and progresses from there to the old wood, causing a dry rot and eventual death of the vine.
Control. - Inspect canes at trimming time, and use care not to leave those on which the brownish black spots are present. Train up renewals from the root, and cut off the old stem below the diseased area. Ripe-rot (Glomerella rufomaculans). - See under Apple, p. 263.
Treatment as for black-rot is efficacious. Shelling or Rattles. - Cause unknown. The berry breaks squarely off at its juncture with the pedicle. The leaves on such vines usually turn reddish brown about the margin. Powdery mildew is sometimes responsible for shelling. Control. - No method is known. Hollyhock. Anthracnose (Colletotrichum malvarum). - Angular brown spots on leaves and stems which spread, killing the entire leaf.
Control. - As for Rust. Rust (Puccinia malvacearum). - Attacks all parts of the plant, causing reddish brown pustules on affected parts ; later leaving deep pits ; may entirely destroy the leaves. It is abundant on the common mallow or "cheeses."
Control. - Eradicate the mallow ; pick off diseased leaves in the fall, and burn all litter. Repeat in the spring, and spray new growth thoroughly with bordeaux mixture, 4-3-50. Spray every week until the flower-stalks are well developed. Lettuce. Leaf Perforation (Marssonia perforans). - Dead areas in the leaves which finally drop out. Also on veins of the leaves. Control. — As for Rosette (p. 274). Downy Mildew (Bremia lactucce). - Yellow spots on the upper surface of the leaf, accompanied by a frosty growth on the opposite side.
Control. - Destroy infected plants. Keep water from the leaves ; furnish water by means of subirrigation.
Drop or Rot (Sclerotinia libertiana). - Base of the leaves or stem rots off, allowing leaves to drop.
Control. - Sterilize the soil with steam before planting. See under Steam in Chapter XV, p. 253. Rosette (Rhizoctonia sp.). - A rotting or damping-off of the stem. Late affected plants have a rosetted appearance.
Control. - Start seed in steam-sterilized soil, and transfer to beds that have been sterilized with steam, as for Drop. Muskmelon. Anthracnose (Colletotrichum lagenarium). - Dead spots on the leaves and stems and sunken pits on the fruit. Thorough and frequent spraying with bordeaux mixture will hold this disease in check. Downy Mildew. -The same disease as on cucumbers (p. 270). Often very destructive.
Control. - A satisfactory method is not known. Spraying as for cucumber mildew has not proved effective.
Wilt. - See Cucumber. Nectarine. Yellows, etc. See under Peach, p. 276. Nursery Stock. - Foliage on young trees is apt to be attacked by various leaf-spot fungi. The damage comes in reducing growth, thus often making seconds. Several applications of bordeaux mixture to keep the new growth protected are beneficial. Oats. Rust (Puccinia coronata). — A red rust of the blades. Control. - There is no known method of control. Smut. - See under Smut of Cereals, p. 260. Onion. Mildew (Peronospora schleideniana). - Causes a wilt or blight of the leaves.