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This Week in the Garden: How to win the war of the roses


Fungal infection to your roses presents as black spots on the leaves. (Sharon Hull -- Contributed)

Fungal infection to your roses presents as black spots on the leaves. (Sharon Hull — Contributed)








Roses have been especially spectacular this spring. All over our area, rose plants have produced a giant showy mass of blossoms, at least in part because of our abundant winter rains. But alas, along with the abundant flowery growth has come a rampant scourge of the dreaded fungal disease Black Spot. If you look more closely at many of those gloriously flowering shrubs and vines, you’ll notice signs that the foliage has problems. Small black areas appear on some leaves, then as the fungus spreads, more and more leaves become diseased, eventually turning yellow and dropping from the plants. If left untreated, the disease can eventually completely defoliate the plants, making them not only unsightly, but also weakened, since the leaves are the energy-producing engines for the plants. Most active in damp humid weather, this disease thrives in our mild summers when daytime temps tend to be in that range. The spores can germinate, proliferate and become visible in three to ten days. The cycle is repeated about every three weeks throughout the summer. It can spread to all susceptible plants in a garden unless the gardener takes steps to control it.

What is an organic gardener to do? We do have some options that are environmentally sound.

First in my arsenal is the organic control called Serenade which has proven quite effective for me in past years. This biological treatment contains a unique, patented strain of Bacillus subtilis which attacks many fungal diseases without harming the plant itself, or endangering other organisms including the gardener. (Remember this product if you have had problems with tomato blight in past seasons. It can be used right up to day of harvest, though it is most effective if application begins well before a fungal disease becomes entrenched.) Serenade is available in local garden centers. You will find more information here: www.bayeradvanced.com/serenadegarden.

There are a number of other commercially-made organic fungicides as well. For example, the well-known Safer brand sells a fungicide containing sulfur. Sulfur was for many years the most widely used treatment for fungal diseases, and is still used by organic farmers today on specific crops. Safer Garden Fungicide is said to control powdery mildew, black spot and rust on roses, as well as fungal diseases on other ornamentals and on vegetables. . This product is approved for use on organic farms by the Organic Materials Review Institute (OMRI.) Many people also report good control using a Neem or horticultural oil spray.

In addition to over-the-counter products, you might choose one of the time-honored homemade methods used for many years by both farmers and gardeners. Baking soda is a common household ingredient, and can be used as a fungus preventative. Combine 1½ teaspoons of baking soda with a teaspoon of vegetable oil and a gallon of water. Spray to combat black spot, rust or powdery mildew every 5 to 10 days until the solution drips off the plants, and spray more frequently in rainy or humid weather. A long list, including recipes, for many other home-brew fungal treatments can be found here: mastergardenergirl.wordpress.com/list-of-homemade-organic-recipes/.

In addition to treatments, sanitation is important to prevent the spread of fungal and other rose diseases. Remove and bag infected foliage (do not put diseased material in your compost bin!) and keep fallen leaf debris removed from around your plants. Irrigate using drip or soaker hoses so that water doesn’t get on the foliage. Prune to allow light and air circulation into the interior of your plants. And when choosing new rose varieties, select those that have the designation “disease resistant.”

Garden tips are provided courtesy of horticulturist Sharon Hull of the San Lorenzo Garden Center. Contact her at 831 423-0223.

Article source: http://www.santacruzsentinel.com/lifestyle/20170518/this-week-in-the-garden-how-to-win-the-war-of-the-roses