Some zinnias will resist mildew

Last week we covered flower bed problems, including powdery mildew on zinnias. This week, the focus is on disease-resistant zinnias that take the heat and avoid powdery mildew. Powdery mildew strikes zinnias worse than almost any other annual. Zinnias with the disease lose their bottom leaves, and their upper leaves are covered with gray powder, which is the mycelium of the fungi growing on the plant.

For centuries, zinnias have graced gardens and spread their glorious colors throughout flower beds and in vases, but they were not always as highly prized. When the Spanish first saw zinnia species in Mexico, they thought the flower was so unattractive they named it "mal de ojos," or "sickness of the eye."

Although I have never shared their opinion, I admit that the gray mold covering the leaves does make a sick-looking flower.

If you want to grow zinnias, you have a few choices to make.

You can grow them and let the fungus take its course, but the zinnia beds will start looking bad about mid-August. As an alternative, you could buy expensive fungicides and spray your zinnias every couple of weeks to control the disease.

If neither of these has any appeal to you, there is another choice. Resistant varieties make a good integrated pest management tool for controlling diseases and insects. These varieties naturally resist pests and they require no sprays to keep them looking good.

While there are not resistant varieties for all pests, there are excellent choices for zinnias. Interestingly enough, many new varieties owe their resistance to older varieties from remote locations. Zinnia angustifolia is considered by some to be the original zinnia that the Aztecs grew in their gardens.

Zinnia angustifolia Orange Star (sold as Z. linearis), Star White and Old Mexico (Z. haageana) have narrow ( 1/2- to 1-inch-wide) leaves with 1 1/2- to 2 1/2-inch-wide daisy-like flowers. These spreading plants are less formal-looking than the other zinnias, but all of the narrow-leafed varieties are considered disease resistant.

One of the first was Rose Pinwheel, a mildew-resistant zinnia released in 1988. It has 3 1/2-inch single dusty-rose flowers on tidy 12-inch-tall plants. The Pinwheel series was expanded to include gold, orange, pink-on-white and white flowers.