- Water plants regularly during dry spells, and mulch the soil to prevent moisture loss
- Climbers and ramblers grown in situations with good air circulation (e.g. over arches, rope swags or pergolas) are less likely to be affected than those grown in still air (e.g. planted closely against walls, in sheltered corners, etc.). Bush roses grown in sheltered situations are also more likely to be attacked
- Feed regularly to encourage strong growth, but avoid using too much nitrogen – this produces ‘soft’ growth which is prone to attack
- Badly affected shoots are best pruned out and disposed of as soon as the symptoms are seen. During routine spring pruning any shoots showing large patches of mildew around the thorns should also be cut out
- There are considerable differences in susceptibility between rose cultivars. However, any claimed resistance to the disease may not persist for the lifetime of the plant, or be effective in all localities
Like that of most powdery mildews, the majority of the growth of rose powdery mildew is on the surface of the plant. This exposed growth makes it susceptible to a range of chemical control measures.
Some of the fungicides available for the control of rose mildew will have activity against blackspot and rust, which are also common and damaging diseases. These include myclobutanil (various products, including Bayer Garden Systhane Fungus Fighter*, Bayer Garden Fungus Fighter Disease Control* and Doff Systemic Fungus Control), tebuconazole (Bayer Garden Multirose Concentrate 2) and triticonazole (Scotts Fungus Clear Ultra, Roseclear Ultra).
Some formulations also contain insecticides but these are best avoided if no insect pest problem is specifically identified. For example, some formulations of myclobutanil (Westland Rose Rescue) contain cypermethrin, some formulations of tebuconazole (Bayer Garden Multirose Concentrate 2) contain deltamethrin, and some formulations of triticonazole (Scotts Roseclear Ultra and Scotts Roseclear Ultra Gun) contain acetamiprid.
Plant and fish oil blends (Vitax Organic 2 in 1*) and the sulphur and fatty acids formulation (Scotts Nature's Answer Natural Fungus and Bug Killer*) may also be used but the latter must be kept away from fish.
Fungicides are likely to need several applications during the growing season, particularly in still, humid weather. Sprays in late summer and early autumn may help to reduce the number of infected buds in which the fungus can overwinter.
*NB: The following products are being withdrawn:
Myclobutanil (Bayer Garden Systhane Fungus Fighter concentrate and Bayer Garden Fungus Fighter Disease Control). These products cannot be sold after the 30th November 2015 and remaining stocks must be used or disposed of before the 30th November 2016.
Plant and fish oil blends (Vitax Organic 2 in 1). These products are being withdrawn but as they are not registered fungicides there is no date by which stocks have to be used up before.
Sulphur and fatty acids (Scotts Nature's Answer Natural Fungus and Bug Killer).This is still legal to sell and use but Scotts are no longer actively selling the product.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)