This is the time of the year when the roses are showing us their best. The rose is the most popular flowering plant in America; however, to have healthy plants with plenty of flowers, you must be prepared to put plenty of work into them. Roses need to be maintained more like a vegetable garden than like most shrubs and perennials. They need plenty of nutrients and plenty of water to enable them to produce nonstop flowers. In fact, in order for one perfect flower to be produced, a plant needs about thirty or so leaves. Roses are subject to a number of diseases here in western Washington which, if not controlled, will cause the plants to look unsightly and prevent them from producing the spectacular flowers that we are all familiar. Diseases can also be bad enough to cause the decline and eventual death of highly susceptible varieties. Three fungal diseases attack rose leaves: Black Spot, Powdery Mildew and Rust. Treatment and control are essentially the same for all of them starting with good plant sanitation. A variety of sprays are available. The most common ones used are lime sulfur, Benlate (Benomyl), and Funginex. Sulfur dust is used also. In applying any of these materials be sure to read and follow label instructions. Here is what you can expect to see if you have any of these fungal diseases. Black Spot is caused by a fungus that overwinters on old diseased leaves and infected canes. What you see are circular black spots on the leaves, often with fringed margins. Yellowing of the leaves and defoliation is very common and in wet weather or with lots of overhead irrigation, the spots can become so severe that they run together to make large spots that can cover a third or more of the leaf surface. Powdery Mildew is a very common fungal disease attacking roses. Almost everyone who has owned roses has seen this problem. It appears as white powder on the newer leaves, shoots and buds. New growth is commonly distorted, and, when the disease is severe, the new growth is badly stunted. The important thing about this problem is that it can occur even in dry weather. Controlling this disease requires an application of lime sulfur spray during the winter. If your rose leaves are turning orangish on the undersides then they are most likely suffering from a disease called rust. This problem can occur on both sides of the leaf, but is heaviest on the undersides. The upper leaf can appear mottled and chlorotic. Later in the season the orange turns to black, a signal that the over-wintering stage has set in. Roses can be beautiful if well cared for. If you want additional information about these problems of roses and some of the insect problems, there are a number of good publications available from our office. One called "Roses for the Home" covers most of the common problems. Since Powdery Mildew is common to our area and to plants other than roses, we have a publication which deals with it specifically. One other good publication called "Plant Sanitation" gives you a good understanding about what we mean when we refer to plant sanitation. All publications cost 50 cents or less. Call and we will gladly mail you a copy.


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