The most common orchid fungus diseases are:
- Bacterial Brown Spot begins as a soft, watery lesion, usually on the orchid’s leaf, that eventually turns brown. In advanced stages, the brown spot will begin to exude a foul-smelling dark liquid.
- Bacterial Soft Spot (also called Erwinia) begins as a nasty-smelling wet spot on the orchid’s leaf. The infected area will expand rapidly and within 1 to 2 days the entire leaf will become soft and slimy.
- Fungal Crown Rot is the most common and dangerous orchid fungal disease. At its beginning, orchid owners may notice a subtle discoloration at the center of the plant or at the base of the leaves. Crown rot is caused by a combination of over-watering, poor air circulation and low temperatures. If untreated, plants can die within a week.
Water residing in a pool in a bract, or on a leaf will be a good place for the fungi spores to settle. The leaves resistance is lowered as it becomes water-logged and gives a point of entry for the spores. Watering early in the morning allows such water to evaporate as the day warms up. Watering in the evening allows that water to remain there longer during the cooler night. Good potting mix will dry out rather quickly after watering. Potting mix that is old can take longer to dry out, if at all. This damp place for the roots is ideal for fungi to become lodged to attack the roots and pseudo-bulbs. Roots need the solid, liquid and gas states to remain healthy. The solids – bark – gives the roots somewhere to grow to support the plant. The liquids – water and fertilizer – supply nutrients. The gas – air – allows the roots to dry out and breathe.
Any cuts or damage to your plants, especially during division, should be sealed with a dusting of Mancozeb, Mancozeb Plus, Tomato Dust (Sulphur), Rose Dust (Sulphur) or Dusting Sulphur. This will seal the cut and prevent fungal attack. Think of root damage that occurs during re-potting. Those scars will need to be sealed too. Make sure all cutting implements are sterilized after each cut. The cleaner your orchid house the better.
To control orchid diseases:
Immediately remove infected foliage using a sterilized razor. Relocate your orchid to expose it to better air circulation, lower humidity and optimum temperatures. Spray your orchid with a good quality, broad-spectrum fungicide, following package directions. Even if you suspect a bacterial disease, fungicide application will prevent secondary infection.