Cultural Control of Plant Diseases

Many people believe that control of plant diseases always mean the use of chemicals, but many diseases can be controlled by cultural practices.

Selection of plant material will greatly affect the amount of disease problems. Some plants are very susceptible to diseases while others have very few, if any, disease problems. The use of native plants can reduce the incidence of plant diseases.

Some diseases such as the powdery mildews and Botrytis blights are encouraged by high humidity in plantings. Losses can be reduced by not crowding plants. Thin the plants to permit free air circulation and allow sunlight to reach the lower parts of the plants and soil.

Diseased branches and shoots should be removed and discarded before a disease can spread. In routine pruning, always remove diseased or unthrifty growth first and then prune to develop and shape the tree or shrub.

Many disease organisms carry over from one season to the next on fallen leaves. It is advisable to collect and dispose of this diseased foliage. Do not include diseased material in the compost heap because of the danger of survival of disease organisms and subsequent spread.

The maintenance of a balanced fertilizer and water program generally produces plants which have some resistance to plant diseases. Some diseases such as certain cankers are more prevalent on plants that are nutrient deficient or suffering from drought. However, other diseases such as rusts and powdery mildews are more severe on succulent growth. High fertilizer content, especially nitrogen, and abundant moisture will favor these diseases. Excess soil moisture may also lead to root rot problems.

When a disease problem develops in a planting, particularly of annuals or succulent perennials, the gardener should consider moving the planting to a new location. This is the same as crop rotation that is commonly practiced by farmers. It permits the plants to grow in soil relatively free of disease organisms and also hastens the natural decline of these disease organisms in soil where they have built up because of the growth of susceptible plants.

Plant in a location suitable for the plant. Don't put shade-loving plants in exposed situations or sun loving plants in the shade. Also, avoid extremely wet or dry locations unless plants are suited to these conditions. Many root diseases are favored by wet soils. Creating good drainage may reduce the severity of these diseases.

Plant at the most suitable time of the year to ensure survival and good growth of the plant. Check with your County Extension agent as to the best planting time for various plants.