Last summer, Bunkey dug up all his phlox. He got tired of spraying them for powdery mildew one week just to see it come back the next humid week. He had stopped planting monarda for the same reason, even though he really liked both plants. This spring he can plant both phlox and monarda (bee balm) with resistant varieties. In a mass planting of phlox at the Brandywine Conservatory in Pennsylvania, a sharp-eyed researcher noticed that one white plant, David, had none of the mildew that the rest of the planting had. The horticulturists began propagating David and it was named the Perennial Plant of the Year in 2002.
Resistance isn’t discovered by accident but is a trait that researchers actively breed for. A plant may be planted at many different sites to see how complete the resistance is and if it functions under different site conditions. This allows the researchers to make certain that the potential plant didn’t just avoid the disease, but resistant. To be very sure the plant didn’t just escape the disease but is resistant, the resistant cultivar is inoculated with the disease.
One of the most recent methods of developing disease resistance is by adding foreign DNA that has a gene in it to give resistance to a given disease, into the plant genome. This results in a transgenic plant. The first gene the scientists used was a protein called luciferase. This is the active enzyme that makes the firefly glow. The result was a plant that was able to light up and glow in the dark. I don’t know about you but the idea that my flower garden lights up at night sounds like a fantastic idea. You wouldn’t need a yard light. Wow!
This was the start of GMO corn, and soybeans and potatoes with BT toxin that kills any potato bugs that bite the leaves.
The research has developed a whole new line of phlox. Look for “Rubymine,” “Goldmine,” a variegated variety, “Laura,” “Miss Lingard,” “Eva Cullem” and “Katherine.” There are four monarda that are resistant and should be available locally. They are “Marshall ‘s Delight,” “Gardenview Scarlet,” “Fireball” and “Jacob Kline.” A rust resistant “Hollyhock,” “Happy Lights” for the people who like “out house” plants, so called because they were often planted around the out-house to shield it from view. Some of the Wave petunias that are grey mold resistant are lavender and “tidal wave.” By this spring there will probably be more. Zinnias were another plant that often-got powdery mildew. One, Profusion, is listed as tolerant. In other words, it may get the mildew, but it really doesn’t care. Actually, it really means that mildew will not kill the plant.
Even if you don’t plant resistant varieties, there are other practices that all gardeners can use to prevent disease problems in your gardens. With phlox, thin stems to 4-6 stems. Give your plants elbow space. They need to be far enough apart for air to circulate. This is especially important in humid weather. If possible, water the soil not the plant. This reduces both humidity and moisture that is necessary for both spore germination and spread. Damp leaves, especially if it is at night can lead to all kinds of problems.
Bunkey is searching for one of those “light up at night” plants. So far, none of his seed catalogs list any.
Bev Johnson is a Master Gardener with the University of Minnesota Extension. Her column appears in the Weekend Edition.