When It Comes to Fungus, Think Prevention
Question: Last spring’s relatively cool temperatures and high humidity caused major fungus problems with my rosebushes. Got any suggestions?
--J.S., Los Feliz
Answer: Rust and mildew were epidemic everywhere last spring, and now--after roses have been pruned but before they leaf out--is the time to prevent a repeat. After-the-fact cures are often ineffective or short-lived.
Begin by picking off last year’s leaves and raking all leaves off the ground. Send them to the dump, not the compost pile. Then soak the bare canes and the ground with environmentally friendly dormant oil and sulfur sprays (available at nurseries). This will help keep last year’s diseases from infecting this year’s roses.
Chemist and rose author Tommy Cairns says preventive measures like these are the best approach, yet “people are reluctant to do anything in winter when they can’t actually see the disease.”
Control is difficult once diseases start. There is no silver bullet.
After roses begin to grow, Cairns says, Funginex does a fair job preventing rust and mildew if you apply it before you see the diseases and if you reapply at intervals suggested in the directions.
Make sure you spray the undersides of leaves, which is where the orange rust fungus grows.
He says Fungi-Fighter (Bayleton) is useful on very large shrubs or on climbers. It is a systemic, and can be poured on the soil at the base of the plant and will be carried by the plant to the leaves. It can also be sprayed.
At the Huntington Rose Garden, Clair Martin is also a big believer in garden cleanup and dormant sprays. During the growing season, “we do nothing,” he said. “We try to prevent disease, not cure it.”
On already infected bushes, you can pick off rust-infested leaves, or use a homemade baking soda solution on rust and mildew, although the diseases usually return.
To a cup of water, add 1 1/2 tablespoons baking soda, one tablespoon Canola oil, one tablespoon insecticidal soap and then--after the other ingredients are added--one tablespoon vinegar. Add enough more water to make one gallon of spray solution.
Don’t apply this homemade spray when temperatures are above 75 or 80 degrees, or it may burn foliage.
Rust makes rose fanciers particularly desperate. In her nursery newsletter, Mary Lou Heard of Heard’s Country Gardens in Westminster, told about the most radical control for rust ever, learned from an old nurseryman: Set the ground on fire.
She said that burning a little shredded newspaper or excelsior under a bush killed rust spores on the undersides of leaves. The quick fire may kill a few leaves, but most are unharmed because they are moist and green. Still, she keeps the garden hose handy just in case. “It really does get rid of the rust,” she said, but it sounds like desperate measures to me.
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Q: A gray mold completely wiped out the crop on my nectarine and peach trees and those of my neighbor this year. The mold starts out as a small soft spot as the fruit begins to ripen, and eventually covers the entire fruit and some of the short branches. What should I do?
--L.L., Camarillo
A: What you are describing sounds like brown rot (various species of Monilinia), the most common disease of stone fruits, especially peaches and nectarines, and very difficult to eliminate.
It thrives in wet weather, so last year’s El Nin~o brought on lots of brown rot. To get it under control, begin by removing and disposing of all shriveled fruit “mummies,” which often hang on the tree for a year or more. Also remove all dead, dried flowers. These are where the mold spores come from, although they are also harbored on branches. (Sounds like you need to get your neighbor to cooperate too.)
Send infected leaves and flowers to the dump; don’t recycle them. Small, velvety gray or tan spores start on spring’s flowers, which then infect the fruit. The first sign of brown rot is the shriveling of the flowers, which persist on the tree and don’t fall off.
As buds swell in spring, but before they open, spray them with copper-containing Bordeaux mixture, Liqui-Cop or Daconil (available at nurseries). These only work as preventives.
If it rains after you apply these dormant sprays, you may have to spray again at full bloom and after the flowers fall.
As flowers open, prune out any that are diseased and send to the dump. As fruit forms, again carefully watch for the disease, which begins as brown or tan spots that quickly enlarge. Pick these too and send to the dump to try to control the spread.
Once fruit forms, it may be too late to do anything, although spraying with Bordeaux one to three weeks before harvest might help (but the copper in it might also damage the tree’s foliage).
One other tip: Keep foliage and fruit dry. Water trees from below.
Got a burning question about a plant, a pest or gardening in general?
Send it to Garden Q&A;, Southern California Living, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053, or fax your question to Garden Q&A;, (213) 237-4712, or e-mail it to socalliving@latimes.com.
Make sure to include your name, city or locale, and phone number in case we need to clarify questions. Telling us where you live is especially important, because gardening problems in Pacific Palisades and Palmdale are quite different. Don’t mail or try to fax dried leaves or flattened bugs because they seldom survive the experience, but photos of problems are OK, even helpful. (Sorry, photos cannot be returned.) We cannot answer questions individually, only in print.
