Sunflower Pests & Diseases

Mildew

• Several diseases may affect sunflowers, and the strength of these diseases determines the quality of your flower. According to the Alternative Field Crops Manual, the most serious diseases of sunflower are caused by fungi. Downy mildew, a cotton-like fungus that forms on the underside of the leaves, creates a discoloration and swelling in the base of the plant. Downy mildew occurs most often when there is rain before the plant breaks through the soil. Similarly, powdery mildew causes a cotton-like fungus to develop on the leaves, though its damage is minimal.

Fungal Diseases

• Leaf spots may cause dead blotches to form on sunflower leaves, but this rarely causes serious loss. Damaged vascular tissue is caused by Verticillium wilt, normally found in the stem's cross-sections. Rust on the flower results in rust-colored pustules forming on the leaves and black specks on the stems. Head and stem rot create a tan ring around the stem at ground level. Discoloration of the seeds and inside of the stem indicates gray-black wilt which rots the heads and stem. Finally, large black splotches may develop at the flower's maturity if the sunflower experiences black stem. Implementing strict rotation cycles can greatly minimize the chance of disease caused by fungi.

Sunflower Moths

• Insects play a large role in the deterioration of sunflowers. Several pests are specific to sunflowers. The larvae of three moths -- the sunflower moth, banded sunflower moth and sunflower bud moth -- feed on the heads of sunflowers. The sunflower moth lays its eggs at flowering and they hatch one week later. These moths feed on the floral sections and tunnel into the seeds. Banded moths feed on the meat by tunneling through a small hole made in the seed. Headless flowers, damaged heads or a large hole on the stem near a leaf petiole may be symptoms of bud moths. These insects feed on the stem and head during the early stages of growth.

Other Pests

• Other fast-growing plants will compete with sunflowers for sunlight, moisture and nutrients. In doing so, they may affect the sunflower's growth. Sunflowers persevere against weeds with regard to sunlight, but ground coverage remains an issue when preventing the establishment of weeds. Growers should implement both cultural and chemical methods when fighting weeds. Annual weeds create the most trouble for sunflowers, while perennial weeds are a minor threat.