There are many different plant diseases caused by fungi, bacteria and parasites, and no plant is entirely immune to disease. Some plant diseases can be easily prevented and treated, while others almost certainly mean the immediate death of the plant.
Phytophthora Root Rot
Phytophthora root rot is a fungal disease that causes damage to plant stems and roots. Signs and symptoms of this disease include scaly and peeled stems and discolored or dead foliage. Phytophthora root rot can cause a plant's leaves to curl at the edges. According to the University of Minnesota extension, overwatering and conditions of poor drainage are typical causes of this disease. Too much water is the single most common cause of Phytophthora root rot. To help prevent it, place your plant in well-draining potting media, like a bark or gravel mixture. Be careful to not overwater. A fungicide may be the right choice if infestation has already occurred. Some fungicides may even work as a preventative method, warding off root rot before it has a chance to take hold.
Leaf Spot and Rust
Leaf spot is caused by a fungus that thrives in cool, wet weather. It is most often a problem in early spring to early summer and rarely occurs during hot weather. It appears as circular spotting on the upper sides of plant leaves, eventually leading to leaf destruction and defoliation. Once the characteristic signs appear on the leaves of your plant, it may be too late to apply a chemical treatment. Leaf rust is caused by a similar fungus. It produces a powdery residue on the undersides of plant leaves. The color of the powdery rust can vary and may appear yellow, brown or orange. Prevent the spread of these diseases by removing any affected plant material and any fallen plant debris. Although leaf spot and rust can make your plant look undesirable, they usually have little effect on the overall health of the plant.
According to a Cornell University factsheet, botrytis blight is most often caused by Botrytis cinerea. It occurs during cool, wet weather and rainy spells. It can cause spotting and distortion of all parts of a plant. Control the spread of botrytis blight by removing diseased leaves, buds and fruit, if any. Remove any fallen plant debris from the base of the plant. When botrytis blight is present, it is best not to use dense mulch, which can hold in moisture and create a breeding ground for disease. A fungicide may be helpful once an infestation has occurred. Choose the appropriate product for your plant and follow label directions.