Common Rust Control



Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales (previously also known as Uredinales). About 7800 species are known. Rusts can affect a variety of plants on the leaves, stems, fruits and seeds. All rusts are obligate parasites, meaning that they require a living host to complete their life cycle. They generally do not kill the host plant but can severely reduce growth and yield. Cereal crops can be devastated in one season and trees that get infected in the main stem within the first five years, invariably die.
HOST PLANTS: Common in roses, snapdragons, bluegrass and woody perennials..

SYMPTOMS: Symptoms are circular to elongate (usually 0.2 to 2 mm long), golden or reddish brown to cinnamon brown pustules that appear on the upper and lower leaf surfaces, and less frequently on other above-ground plant parts. Most of the infection is found on the upper leaf surface and may occur in bands. The pustules break through the epidermis early in their development and become powdery as spores (urediniospores) are produced. Later in the season they become brownish black as a second spore stage (teliospores) develops which also breaks through the epidermis. If severe, chlorosis and premature drying of the leaves may occur, reducing sweet corn yields. Symptoms may vary slightly depending upon the hybrid being grown. Common rust is especially severe on many sweet corn hybrids containing the shrunken-2 (sh2) endosperm mutation for high levels of kernel sugars and on some of the sugary-1 (su) hybrids grown for processing.

FAVORED ENVIRONMENT: Rust diseases are favored by 4 to 8 hours of low light intensity, warm temperatures, and high humidity, heavy dews, or light rains followed by 8 to 16 hours of high light intensity, high temperatures, and slow drying of leaf surfaces.

COMMON RUST CONTROL: Choose resistant varieties when possible. Pick off and destroy the infected leaves, and rake under the plants frequently to remove all fallen debris. Water in the early morning hours (avoiding overhead watering if possible) to give plants time to dry out during the day. Drip irrigation and soaker hoses can be used to help keep the foliage dry. Do not compost infected leaves or stems and thoroughly clean up garden areas in the fall to reduce over wintering sites for the fungal spores. Prune plants and remove weeds to improve air circulation.

Sulfur or copper powders/sprays should be applied weekly, starting when foliage begins to develop in the early spring and continuing throughout the growing season. Spray early in the day, and avoid applications during hot weather. These organic fungicides will not kill the rust, but prevent the spores from germinating.

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