Veseys

Canada (Switch to US)

Information for Gardeners

Common Diseases

Veseys Home » Learn » Planting Guide » Growing Roses, Flowering Shrubs, Vines and Trees » Common Diseases

Though there are many diseases that can affect roses, there are three in particular that cause the most problems to home gardeners. They are known as ‘The Big Three’ and include Powdery Mildew, Black Spot, and Rust.

Powdery Mildew

Powdery mildew is recognizable by the presence of a white or grayish powdery coating on the surfaces of leaves and young shoots. It is a fungus. Plants are affected gradually, and the powdery coating is the very first symptom. Remove and destroy leaves that are at all affected to prevent the spread of powdery mildew. If problem is severe, use ‘Safer's Garden Sulphur Dust’, or ‘Safer's Defender’. Do not spray Rugosa Roses, they cannot tolerate any sprays. The good news is that Rugosas are resistant to Powdery Mildew and you probably won’t run into this problem.

Rust

Rose Rust is recognizable by a powdery orange residue on the undersides of leaves. The leaf surface must be continuously wet for four hours for infection to take place. Remove and destroy infected parts immediately, and if severe, treat with ‘Safer's Garden Sulfur Dust’.

Black Spot

A fungus called Diplocarpon rosae, which only affects roses, causes Black Spot. Black Spot is detected by the presence of round, velvety dark-coloured lesions often surrounded by a fuzzy or feathery halo. These spots are usually 2-12mm in diameter and differ from other spots by their ‘fuzzy’ edges. Remember that several of these round lesions can fuse to form an infection of any shape. Leaves will eventually turn yellow and drop off prematurely. A few days after the spots appear, little black pimples show up in the spots; this signals that the spores are about to be discharged and that you had better act fast. Carefully remove and destroy these leaves. Baking Soda solutions will work in most cases by changing the pH on the surface of the leaves, inhibiting fungal growth. To make your own, mix 25 grams of Baking Soda with one litre of water and spray onto leaves. ‘Safer's Garden Sulfur Dust’ and ‘Safer's Defender’ fungicides will do the trick.