I'm about ready to give up on my roses. I have a black spot and mildew problem. I have sprayed (in the past) with Ortho Dormant Disease Control (and will use it again out of desperation), removed affected leaves and branches when black spot is found, ignored the problem, certainly used Bayer systemic feed and insecticide (which doesn't have anything to do with my main problem) and the problem remains.
I do remove dead leaves, etc., diligently. I object to the spray as I suspect it is toxic to humans. This problem is about four to five years in the making and progressively getting worse. Some of my roses get sun until about 2 p.m. and some are in more shade. What pearls of wisdom have you for me?
Nancy Price, Sacramento
You're not alone, according to local consulting rosarians. There have been really bad black spot and mildew problems the last two seasons, due to weird weather. Last year, the problem was too much rain and not enough heat. This winter, the weather has been mild, so roses didn't want to drop their leaves, which became havens for both fungi.
Black spot is a fungus that overwinters in the topsoil and mulch under the bush. Mildew also is a fungal disease that spreads through spores.
After pruning your roses, rake away all the old mulch and any dead leaves, and dispose of it don't compost those leaves. The fungus survives composting and comes back stronger than ever if you use the compost around the roses.
Both black spot and mildew spread more if your roses are irrigated by sprinklers. The water splashes on the plant and moves the spores from leaf to leaf. Switching to drip irrigation helps a lot.
Roses are leafing out very early right now, and those tender first leaves are picking up black spot and mildew, too. Leaves less than two weeks old are most susceptible. They'll likely develop black spot before the rest of the plant gets its leaves. And a whole vicious cycle can begin again.
Black spot "blooms" when temperatures rise to around 70 degrees; reflected heat from buildings, walls, or sidewalks will make the plant feel like it's 70 when the air temperature is still 65. Add a little rain, and spores take off. They need only one day of warm weather to get going; the spots will show up three to 10 days later.
If using the dormant spray, trim any leaves first (and discard them in the trash don't drop them on the ground where spores can fall off).
According to research, sulfur is the most effective deterrent against black spot. You can sprinkle the powder on the bush.
Liquid soap (such as Ivory or Dr. Bonner's) also works pretty well. Trim off and discard any infected leaves first; then dissolve 1 teaspoon in 1 quart of water and spray the leaves (top and bottom) if it looks like an outbreak is about to start.
Another solution uses baking soda: Dissolve 1 teaspoon baking soda in a quart of water, add a few drops of liquid soap to the mix to help it cling better to the foliage, and spray infected plants thoroughly.
Mildew takes off during warm, dry days with cool, foggy nights typical Sacramento winter weather. Mildew actually doesn't like water. If you spray infected leaves with fungicidal soap and water (or a strong blast of just plain water), it can knock down an infestation.
Young infected leaves tend to pucker or crinkle before you see the white mildew; the spores are forming in the funny- looking leaf. If you see a leaf that's wrinkling in an odd way, pick it off and discard it (again, don't compost it). That leaf is about to explode spores all over its neighbors.
But once you see the mildew, you can treat it with baking soda, too. This formula may need to be reapplied after rain since it tends to wash off. One side benefit to the baking soda spray is that insects don't like it, either.
Good air circulation around the plants fights both fungal diseases. If your bushes are crowded together (closer than 4 feet apart), they're more prone to fungi.
Also, roses need six hours of sun a day; the more sun, the less fungi. Your plants are staying cool and a little shady. That's making the problem worse.
Some varieties (especially hybrid teas from the 1960s, '70s and '80s) just seem to be more prone to black spot and mildew. Many new releases are resistant.GARDEN QUESTIONS?
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Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returnedHere's a homemade recipe for use against mildew, courtesy of the American Rose Society:
Baking soda spray
11/2 tablespoons baking soda
1 tablespoon liquid soap
1 tablespoon Listerine mouthwash; regular, not mint flavor
1 tablespoon vegetable oil
1 cup water
1 tablespoon apple cider vinegar
1 gallon unchlorinated water
Pump sprayer (1.5-gallon size or larger)
Mix the baking soda, soap, Listerine and oil with 1 cup water. Add the vinegar last so that the mix won't bubble over. Pour the mixture into the sprayer and add 1 gallon water. Shake to combine. Spray plants thoroughly.