Brown Spots on Newly Planted Sunflower Leaves
Sunflowers (Helianthus annus) are tall, broad-leaved annual plants that produce large flowers with brown faces and bright yellow petals. Within 11 days of planting, the leaves and stalk of the plant emerge. It's best to plant sunflowers from February to April in U.S. Department of Agriculture hardiness zones 7 through 9. Although they are hardy and adaptable, various diseases and insects cause brown spots on newly sprouted sunflower leaves.
Sunflower Plant Leaves
Sunflower rust creates small reddish brown spots with yellow halos on the top and underside of the plant’s leaves. A fungal pathogen called Puccinia helianthi causes these spots. Spores appear during the summer and easily spread to delicate tissue of newly planted sunflower plants. The fungus continues to infect plants through the season, surviving the winter in the soil and affecting sunflower seeds planted the following season.
If untreated, sunflower rust damages and kills the plant. Eliminate sunflower rust by choosing hybrid, short-season plant varieties, or plant your sunflowers early in the season. If signs of sunflower rust appear on new plant leaves, apply fungicides specially formulated for sunflower rust.
Sunflowers are a moisture-loving plant. Without sufficient water, new plants are susceptible to fungal wilting. Fungi living in the soil attack sunflowers, moving upward and causing dark brown spots on the leaves and stem of the plant. New plants also appear wilted and dry. The difference between a genuine lack of water and fungal wilting is noticeable within one to two days of watering your sunflower plants. If the plant appears wilted after receiving sufficient water and has brown spots on the leaves, fungus is the culprit.
Unfortunately, there is no quick fix for this problem. If your newly planted sunflowers are affected, they must be removed immediately to prevent further infection. If you plant sunflowers again, you must move them to a different area of your garden, as they should no longer be planted in the affected soil.
If you notice brown spots on your newly planted sunflower leaves, look closer. If the spots are moving, it is insects, and not a disease or fungus that is affecting your plant. Sunflower beetles are present in most parts of the United States. These 1/4-inch-long insects have brown heads with white bodies and distinctive brown stripes. They appear during the spring and summer to feed on new sunflower leaves. Discourage sunflower beetles from feeding on your new sunflowers by treating your plants with an organic insecticide.
Carrot beetles also feed on new sunflower plants. Attacking both the leaves and the sunflower roots, carrot beetles cause the plant to appear wilted and dry. These 1/2-inch-long brown bugs stunt the growth of new sunflowers if the plants are heavily infested. Keep your plants free from carrot beetles by removing dead and rotting vegetation from your garden landscape and treating your plant with a natural or organic insecticide.
Temperate Mediterranean climates create the perfect environment for fungal diseases that affect sunflower plant leaves. Pathogens that contribute to leaf disease live in the soil and infect seeds as soon as they are planted. As the leaves of the new plants emerge, they are covered in brown spots. The leaves also appear delicate, dry and are susceptible to tears and breakage.
Without treatment, new sunflower plants wilt and die. Treat leaf diseases with organic fungicides formulated for sunflowers. Leaf disease is also avoidable by making sure that sunflowers receive adequate light, as they are a full-sun plant. Shade and lack of space between plants make sunflowers vulnerable to leaf diseases.
- University of Florida IFAS Extension: Helianthus Annuus "Sonja" Sonja Sunflower
- University of California Agriculture & Natural Resources: Pests in Gardens and Landscapes
- University of Minnesota Extension: Rust in the Flower Garden
- University of Minnesota Radcliffe's IPM World Textbook: Sunflower Insect Pest Management in North America
- North Dakota State University: Sunflower Disease Diagnostic Series