Because sunflowers are native to North America and have evolved with plant pests, there are more sunflower diseases found in North America than in other parts of the world. There are 30 or more known sunflower diseases but nine diseases are the most commonly seen. Septoria leaf spot, powdery mildew, Rhizopus head rot, and charcoal stem rot are occasionally observed but seldom cause more than very localized yield reduction. Fungicidal protection against foliar diseases in sunflower is not normally economical. The exception is when new rust races develop and before resistance genes have been incorporated into commercial varieties.
Seed treatment can be economical in areas prone to downy mildew.
Growing resistant varieties and using pest management practices are the best ways to maximize yield.