5 COMMON DISEASES

Mildew and black spot are the two commonest rose diseases. Mildew is white and powdery, black spot is just that – large black spots that eventually coalesce and cause leaf drop. Solution Plant roses with thick, leathery leaves that are naturally resistant to these diseases. Grow plants in rich, moisture-retentive soil (both diseases are most prevalent in poor, dry earth.) In autumn, collect and burn leaves infected with blackspot.

Viruses cause the twisting and disfigurement of leaves and shoots, as well as unwanted variegation – yellowing and streaking. Solution Alas, there is no solution to plant viruses. Dig up and burn affected plants. Encourage birds and predatory insects that control the aphids that spread virus diseases.

Blossom end rot on tomatoes is not a disease but a physiological disorder that causes black sunken areas on the underside of the fruits. Solution Make sure that the plants are never allowed to dry out completely. This disorder is caused by erratic watering and can easily be controlled by keeping the compost evenly moist at all times.

Potato scab causes rough brown scabbing on potato skins. It is unsightly but not harmful and can be removed by peeling. Solution Make sure that the earth around potatoes remains evenly moist during the growing season. Grow scab-resistant varieties that are much less likely to be attacked.

Box blight causes the shoots of box bushes and hedges to turn creamy white and die. Severe infestations will kill the plants. Solution Avoid clipping box when it is wet and the disease is more readily spread. Some new varieties, such as ‘Heritage’, ‘Skylight’ and ‘Renaissance’, are resistant to attack. Plant alternatives such as Ilex crenata and Euonymus ‘Jean Hugues’.