Orchids are a large group of flowers found in warm climates. They can be purchased at home stores and plant nurseries. Their proximity to other plants in nurseries and greenhouses can easily spread pest and mould problems that need to be treated. The appearance of white mould at the base of an orchid can be caused by several things.
Mealybugs are a common orchid pest that leave white, fuzzy, mould-like material all over the base of the orchid, leaves and blossoms. The mealybugs themselves may only be less than a third of an inch long, making it easier to spot the fluffy material left behind than the actual bugs themselves.
White mould can infest the base of an orchid plant if it is overwatered or too moist. This mould is sometimes called snow mould and grows in the potting medium when it begins to break down. The mould doesn't grow on the orchid itself, but it can suffocate the roots and lead to the death of the orchid. Fungicide can be used to treat mould.
Wiping a cotton ball soaked in rubbing alcohol over the stem, exposed roots and leaves of the plant can kill mealybugs, while larger mealybugs can be pulled off of the plant by hand. Insecticidal soap is also a good treatment method, but multiple treatments will be needed until the problem is resolved. Other options include neem oil and mineral oil, used in the same manner as rubbing alcohol.
When bringing a new orchid into your home, inspect it carefully for signs of a mouldy white substance before placing it near other household plants or orchids. Preventive insecticidal soap treatments can be given anyway. To prevent mould growth on orchids, ensure that orchids are not always moist.