Diseases are Just "Dying" to Get to Your Plants
Botrytis (black leg)
Botrytis (black leg): Fungus attacks the stem and spreads throughout the plant.
At this stage it is best to dispose of the plant. Fungicides are used primarily as a preventative and not a cure.
Root Gall is a type of cancer common to the dwarf and miniature varieties of zonal geraniums and also many of the scented varieties of pelargonium. They appear as knotty growths right at or slightly below the soil line. They rob some of the plants Vigor and are easily removed with a sharp knife, take care not to injure the plant.
Fungus attacks the root system and the vegetative top of the plant slowly declines in vigor. Pythium is almost always caused by over watering. As soon as you detect the disease make cuttings as the plant will not survive. There are a number of fungi and bacterial diseases which cause very similar visual affects to one another and it is best to have an expert help with the diagnosis. The 3 most common diseases to affect geraniums in Northern California are shown on this page.
One teaspoon of Baking Soda (Arm & Hammer Sodium Bicarbonate) diluted in one quart of water (use warm water) works well to control Mildew. Repeat every 3 weeks during the period mildew becomes a problem.
Fungus is always a problem as there is sufficient moisture in the Vicinity of the plants to host a variety of fungi including Phytophthora, Pythium and Downy Mildew. This is a liquid systemic when diluted with water as directed can be used as a drench to the pot containing the plant or simply sprayed on the foliage.
Sterilize your hands with Alchool
If you grow a collection of geraniums in a confined area such as greenhouse it is best to use alcohol to sterilize your hands and tools prior to and while working with your plants to reduce the spread of diseases from one plant to another.
Always use care when working with chemicals and read the directions before using the ingredients. Store all of the above mentioned Plant Controls in a cool dark area to maintain the effectiveness of the product. Always follow the recipes as higher dosages can be toxic to the plants.