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Ask Dr. Hort: Black spot on roses is inevitable

Black spot on roses is inevitable

Q: We recently transplanted roses given to us by a neighbor. They seem to be doing fairly well and we have wonderful flowers. We did do some pruning but there are black spots on some leaves. Can you help? Judy

A: Black spot on a rose is inevitable, especially on the thousands of grafted hybrid teas, grandifloras or floribundas. There are cultural measures you can provide to reduce black spot. Prevent irrigation from hitting foliage; make sure that your roses are in full sun; and pick diseased leaves off plants as well as off the ground and discard in the trash.

Begin a pesticide/fungicide spraying treatment program on either a weekly or every-other-week basis. Starting with two of the least-toxic classes would be 70 percent neem oil products like Fertilome Triple Action Plus or Monterey 70 Percent Neem Oil.

A good home remedy is 1 heaping tablespoon of baking soda (sodium bicarbonate), 1 tablespoon horticultural or neem oil and 1 teaspoon dish soap in 1 gallon of water. A commercial preparation, Bonide Remedy, adds the nutrient potassium, an immune booster. Sulfur products like Fertilome Dusting Sulfur or Hi-Yield Dusting Wettable Sulfur or copper products like Fertilome Blackspot Powdery Mildew Control or Hi-Yield Copper Fungicide gives you two more classes of treatment.

Other products are more toxic, but you may try Fertilome Liquid Systemic Fungicide, or Ortho Max Garden Disease Control or Spectracide Immunox Multi-Purpose Fungicide. The goal is to rotate two or three classes of products so the disease does not become resistant, such as rotating 70 percent neem oil and dusting sulfur or copper and a product containing chlorothalonil, such as Ortho Max Garden Disease Control.

All of these products need to be sprayed on a regular basis because they protect the plants before diseases appear. Always read the label for rates, active ingredients, personal protective equipment needed, etc.

For more information on rose growing (and much more), many publications can be found at and

You don't want to touch this plant

Q: Yesterday I picked a weed from my garden and as soon as I touched it, my hand went hot and burned. I thought I had been bitten by something, but saw no ants or sign of a bite. There was no swelling or redness. But the burning feeling through my fingers and hand lasted a day. What happened? I'll certainly use gloves from now on. Joanne Camilleri

A: You have touched a plant commonly called Tread Softly, Cnidoscolus Stimulosus. Its last name says it all. It is also known as spurge nettle and is characterized by maplelike leaves, three to five lobes like fingers. To aid in its identification, it has clusters of star-shaped white flowers. Small poisonous hairs are distributed all over the stems and leaves, and when touched, burn like fire as they break off in your skin like tiny shards of glass. It grows from an underground tuber, so dig it up to remove the entire plant, making sure not to touch any of the above-ground parts.

Need help? Dr. Hort (Greg Charles) answers questions about garden problems. E-mail him at or mail questions to HomeLink, Features Department, St. Petersburg Times, P.O. Box 1121, St. Petersburg, FL 33731. Describe problem in full, and include your name, city of residence and contact information. If possible, include a good-quality photo. Fuzzy ones won't do. Photos cannot be returned.

Ask Dr. Hort: Black spot on roses is inevitable 06/18/11 [Last modified: Friday, June 17, 2011 4:47pm]
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