Leaf Damage on Sunflowers

Insects

• Many kinds of beetles, caterpillars, grasshoppers and other bugs feed on sunflower leaves. Sunflower beetles (Zygogramma exclamationis) can produce enough leaf-chewing larvae to quickly make sunflower leaves resemble Swiss cheese. Other pests that commonly damage sunflower foliage by feeding on or tunneling into leaves include the sunflower bud moth (Suleima helianthana), the sunflower stem weevil (Cylindrocopturus adspersus) and the palestriped flea beetle (Systena blanda).

Sunflower Rust

• Sunflower rust (Puccini helianthi) is a condition caused by a pathogen that targets plants in the Helianthus genus. According to the National Sunflower Association, more than two dozen “races” of sunflower rust have been identified that affect wild and cultivated species of sunflowers. The telltale sign of sunflower rust is the appearance of red or rust-colored blisters on leaves.

Fungal Disease

• Leaf diseases caused by fungal infections typically cause yellowing or browning of leaves. A particular threat to sunflowers is white mold (Sclerotinia sclerotiorum), which originates in the soil. Downy mildew (Plasmopara halstedi) and powdery mildew (Erysiphe cichoracearum) produce leaf discolorations as well as fungal growth on the undersides of leaves. Other fungal diseases that cause damage to sunflower foliage include leaf spot (Septoria helianthi) and Verticillium wilt (Verticillium albo-atrum and Verticillium dahliae).

Wildlife

• Deer love to dine on sunflowers, especially new leaf growth. The most effective barrier is fencing at least 6 feet high or, at minimum, an enclosure of chicken wire supported by stakes. Once the central flower disks go to seed, birds and squirrels will come around. Aside from the obvious vacancies created at the feast site, damage to the leaves closest to the flower head is an indication they are being used as a perch by these animals to reach the seeds. Enclosing the flower heads with a mesh bag or garden fleece blocks their access while allowing light to enter and moisture to evaporate.