Orchid bacterial or orchid fungal diseases may develop when temperatures are high and conditions are humid; they may also spread rapidly if left untreated. To distinguish between the two diseases, look for discolored leaves and a foul smell, this is an indication of a orchid bacterial disease.
Whether it's a fungal or bacterial disease, the infected foliage should be removed using a sterile razor and sprayed with a good fungicide. However, bacterial diseases will not respond to fungicides, yet they should be applied regardless to prevent an orchid fungal disease from forming. Also, move the orchid to a location with lower humidity avoiding water on the leaves at night and a daily temperature between 65 and 80 degrees F.
- Orchid Bacterial Diseases:
Bacterial Brown Spot - This begins as a sunken, water soaked lesion that over time turns brown and will exude a dark liquid.
Bacterial Soft Spot (Erwinia) - Foul smelling wet spot on the leaf that expands rapidly. The leaf will eventually become completely soft and slimy within one to two days.
- Orchid Fungal Diseases:
The most concerning fungal disease to watch out for is Crown Rot. This will appear as discoloration at the center of the plant or at the base of the leaves. If Crown Rot is left untreated, it will quickly kill your orchid within a week. This is caused by water present in the crown of the plant along with low temperatures and poor air circulation.
As soon as you observe this, spray the orchid plant with a good fungicide at the recommended rate. If there are any dead leaves as a result, remove those with a sharp sterile razor and reapply the fungicide.