Diseases

Black spot is the scourge of every rose grower. Most roses at some point will be hit with the disease, which as the name suggests, causes black spots on foliage. This is often soon followed by a yellowing and premature drop of infected leaves. Black scabs can also develop on stems, all combining to prevent healthy growth.

The evolving nature of the disease means that even new resistant rose varieties will eventually be hit by a new strain that they won’t be able to fend off.

To prevent spread, fallen leaves should be removed from the garden and ideally burnt. However, the spores can be carried to any garden on the wind, and aphids too (another common rose problem) can carry the disease plant to plant.

So, to prevent the risk of black spot taking hold on your garden roses, a preventative systemic spray such as Rose Rescue Ready-to-Use should be used at intervals through the growing season. Start this with an application to emerging new growth in spring. Repeat this after the first flush of summer flowers have been removed from the plant. For total control, cover all foliage parts thoroughly, including the underside of the leaf.

Damping off, a seedling disease caused by several different fungi, can hit at any time of year but is most likely to strike in spring, when light levels and temperatures are low. While it can take hold on seedlings outside, it is more likely to occur with seeds sown indoors under high humidity.

The signs are obvious, seedlings seemingly collapse and wither and are occasionally covered in white fluffy mould. It can be very localised – one half of a seed tray may remain unaffected, while the other is lost to the disease.

There are no specific chemical controls for the problem, so prevention is better than cure.

Always use a quality compost such as Gro-Sure Seed & Cutting Compost when sowing seed, and where possible use new seed trays for each sowing you make. If you do need to re-use containers wash them well and disinfect them. Throw away any containers where damping off has been a problem.

Keep seedlings well ventilated to improve air circulation and reduce humidity and avoid sowing seed too thickly to avoid overcrowding.

Use tap water rather than stored rain water, which is more likely to harbour the pathogens that cause the problem.

Always buy quality seed. Varieties in the Unwins Gro-sure seed range have been selected for their pest and disease resistance, and many are pre-treated to further boost their ability to fight off disease problems.

Under favourable conditions, powdery mildew can take hold on many common garden plants, both ornamental and edible. Despite looking similar plant to plant, powdery mildews are often host specific, so the disease when seen on a delphinium will be different to that seen on a grape vine for example. Fortunately prevention and control is the same for each.

The disease is easily spotted. White, powdery patches appear most commonly on foliage but can also affect flowers and fruit.

The disease becomes a particular problem during periods of high humidity, especially when soils or container compost is dry.

To reduce the risk of infection, water plants regularly but avoid wetting foliage. Mulching around plant bases will help keep soils moist, reducing the chance of infection.

Affected plant parts can be removed to reduce spread but, being a surface problem, powdery mildew can be easily brought under control with the use of fungicidal sprays.

Plant Rescue Fungus Killer (available as concentrate or as a ready to use spray) can be used on both ornamental and edible plants. For quick control on ornamental plants apply Westland Rose Rescue. Repeat the application two weeks later for total control.

Powdery mildews overwinter on fallen foliage, releasing their spores in spring to start the cycle all over again. Removing fallen leaves from the garden each autumn will help prevent the problem occurring the following year.

Rust disease is commonly associated with roses but a wide range of trees, shrubs, perennials, bedding plants, bulbs, fruit and vegetables can be affected. Rust is characterized by leaf spots, most commonly on the underside of leaves, which develop into pustules, eventually releasing thousands of spores. These are then spread to other plants by rain splash or air movement. If left untreated they soon reduce the vigour of plants and in severe cases can kill the plant off altogether.

There are various rust disease, many of which appear orangey-brown, leading to the common name, but white, black, brown and yellow rusts are also to be found.

Rusts thrive in wet and warm conditions and are more of a problem during prolonged wet summer weather. If caught early enough, individual affected leaves can be removed, but it is best to prune out affected parts of the plant where possible. This will improve air circulation around the plants and reduce the risk of spread. Do not add affected material to compost heaps.

Once the affected parts are removed, treat plants with Plant Rescue Fungus Killer, available in concentrate or ready to use formulas.  Repeat the application 2 weeks later to ensure total control of this unsightly plant disease.

When buying particularly susceptible plants such as roses and hollyhocks, look for cultivars with increased resistance to the disease. Other commonly affected plants include alliums, antirrhinum,  bluebell, box, chrysanthemum, fuchsia, heuchera,  hypericum, mahonia, pear, poplar and vinca.