Sunflower Diseases & Insects

Diseases

• Sunflowers are susceptible to sclerotinia head rot, sclerotinia middle stalk rot, sclerotinia wilt, downy mildew, powdery mildew and rust. Of all the diseases, sclerotinia is the hardest to avoid in residential and commercial landscapes because it damages the heads, stalks and roots. Caused by Plasmopara halstedii, downy mildew causes yellowing or leaf chlorosis and the appearance of cottony masses on the undersides of infected foliage. Powdery mildew causes a white powdery growth on the upper surfaces of leaves that causes curling, wilting and premature drop. Caused by Puccinia helianthi, symptoms of rust include tiny orange spots on the upper and lower surfaces of leaves.

Disease Management

• To control sclerotinia in sunflowers, avoid growing the plants on infested soils. Practice crop rotation and monitor fields for signs on diseases because a heavily infested field will fail to produce sunflowers for many years. Apply a registered fungicide over sunflowers infested with downy mildew. Treat sunflowers that exhibit signs of powdery mildew with a fungicide containing sulfur. To manage rust, plant disease-resistant varieties whenever possible, and spray mancozeb two times a year, 10 and 35 days after planting. Because good cultural practices greatly reduce the occurrences of diseases, follow a regular watering and fertilizing schedule to build resistance against disease-spreading organisms.

Insects

• Insects that eat roots and seedlings include root weevils, wireworms and cut worms, while pests that damage stems include stem weevils and borers. Flea beetles and sunflower beetles eat the foliage. Sunflowers infested with wireworms wilt, collapse and die. Adult and larvae of root weevils cause severe damage to the roots of sunflowers. Cutworms chew young leaves and cut seedlings down to 2 inches above the soil. While adult damage by stem weevils is minimal, the larvae cause extensive tunnels that cause it to break. Stem borers cause the stems to break at the point of girdling. Flea beetles cause the leaves to appear lacy, while sunflower beetles cause extensive defoliation.

Insect Management

• Apply a registered insecticide for wireworms before planting sunflowers, since there is little you can do once the pest infestation occurs. Treat cutworms with a postemergent insecticide applied at night. Treat weevils with an insecticide in June or July, before females lay eggs. Plant sunflowers later in the season or till the soil in fall or winter helps manage stem borers. Insecticide seed treatments effectively reduce populations of beetles.