Powdery mildew
This can be a problem with house plants, particularly in humid, poorly-ventilated conditions. It appears on any above-ground part of the plant as a white, powdery growth. In the early stages it spreads slowly and will not cause much harm to the plant. Move the plant to a drier location with proper ventilation, and remove damaged parts. A suitable recommended fungicide can be used to control this disease. Powdery mildew spores are spread easily by air currents; they are one of the few fungal spores not requiring free water to germinate. Begonias, African violets and roses are often affected by powdery mildew diseases.

Wilts:
Some types of fungi and bacteria enter the plant roots through the soil and interfere with the water-conducting ability of the plant. Leaves wilt and become pale, eventually turning brown; growth is reduced and the plant may soon die. In this instance the plant may have been infected prior to purchase, the change of conditions having made them more susceptible to disease. Healthy cuttings can sometimes be taken from the upper parts of the affected plant, and rooted in a sterile medium. The pot should be disinfected before reuse.

Crown, stem or root rot:
The micro-organisms that cause these problems thrive in moist conditions, so plants which have become unthrifty as a result of overwatering are highly susceptible to infection. At first, the leaves droop and the plant appears to need water; stems and roots usually turn dark, mushy and rotten; lower leaves become dark and waterlogged. The entire plant may collapse. If detected in the early stages, further damage may be prevented. Place the plant in a dry, ventilated room and withold water until progress of the disease is halted. You may need to remove the damaged portions, rerooting the top part if necessary. Cacti and succulents are particularly susceptible to stem and root rot. They should always be kept fairly dry, particularly during winter months.

Botyritis blight (grey mould):
This fungal disease can develop on any above-ground part of the plant as a result of high humidity or overcrowding, or if dead leaves or blossoms have been left on the plant. Symptoms vary from plant to plant but the disease generally appears as a fuzzy grey growth. Remove old leaves and flowers, increase ventilation and keep in drier conditions. Treatment with a recommended fungicide may be necessary.

Leaf-spots, flower spots and blight:
The spores of these fungi are spread by air currents or water. Infection only occurs under moist air conditions or if standing water is left on the foliage for prolonged periods.

Damping off:
This covers a number of soil-located fungi which attack seedlings and cuttings, causing them to rot at the base. Affected plants collapse and die. Damping off fungi also cause seed decay. This should not occur in proper conditions. Use a sterile porous rooting medium; avoid overcrowding of seedlings; do not overwater and choose a well ventilated area.