Mold on Rose Plant

Overview

The rose is one of the most popular plants in America. Powdery and downy mold are the two biggest mold problems of roses. Botrytis blight is a fungus type mold but does not show up as often as others. Many molds can be minimized through sanitation, resistant varieties and proper treatments.

Powdery Mold

Powdery mold is a common disease of roses worldwide. It has a high reproduction rate. It is a white powdery growth on leaves and buds. Early appearance of powdery mold appears as white or reddish spots on the leaves. This type of fungus can also have small black patches on the surface of the leaves that can survive through winter months. Powdery mold increases during the hottest summer months. The mold decreases the nutrients to the roses. It spreads through wind and rain to other roses.

Downy Mold

Downy mold is a highly destructive disease of roses. It develops in cool, wet conditions. The fungus develops on all above-ground parts of the plant. Infected leaves have purple or red spots on the leaves and are easily spotted on the top of the leaf. Yellowing and premature leaf drop can also occur. During high-humidity days a purplish gray moss begins to appear on plants and bottom of leaves, increasing the destruction of the plant. Purple black lesions will begin showing on the canes as the mold increases.

Botrytis Blight

Botrytis blight causes mostly cosmetic symptoms for roses. It develops mainly on hybrid tea roses. Symptoms can be found on all above-ground parts of the plants. This mold grows quickly during cool, cloudy and humid weather. This mold is a grayish brown fuzzy growth and small tan patches occur on the flower petals. The buds may droop and not open. This fungus can survive on all type of plant debris, not just roses.

Prevention and Nonchemical Control

Choose resistant varieties when buying roses. Avoid wounding plants when transplanting. Molds develop on wounds or scarring of wounds. Plant roses in an area with good drainage and good ventilation. Avoid overhead watering; water on the leaves can promote growth of mold. Prune, collect and destroy all debris that may be infected. This will not prevent the disease but can restrict it. These diseases are spread by wind and rain.

Chemical Controls

When using fungicides, use only registered products. Nonregistered chemicals may cause the mold to worsen or even destroy your plants. Do not use the same product for every treatment; this can cause the plants to build a resistance to that product. Fungicides containing mancozeb, myclobutanil, penconazole. and plant and fish blends may all be used for this type of mold and are registered products. Avoid using fungicides mixed with insecticides unless you need an insecticide.