Flower buds yellow and drop. Apply N immediately. Slow growth, purple tinged small leaves that feel fibrous. Fruit set delayed. Very long, narrow, yellowed leaves mottled with dead spots.
Manure is simplest cure.
Most can be treated with Bordeaux Mixture, Kocide micronized copper, copper dust, and sulfur sprays and dusts. Most prominent in hot Augusts with high temps and humidity or heavy dews. Fungus can overwinter on vines, or can be seedborne. Rotations and treating seeds with 122oF water for 15 minutes can help control. Also Bordeaux mixture.