|Black spot looks
exactly what the name describes. The surface of the plant will
develop blackish areas on the epidermis. Depending on the
type of rot, these spots may be either wet or dry and may extend
underneath the dermal surface. Wet rots are much more serious
than dry rots. One of the more common wet rots is caused by
phytophthora, a fungus. If these show up, it is best to discard
the plant and start over. Because this disease can be spread in
contaminated soil, it is best to throw the whole pot in the
trash. Donít think to recycle the potting soil it will simply
spread the disease to other plants.
This diseases are due principally to inadequate cultural
conditions like low winter temperature, poor ventilation,
overwatering and excess of nitrogen. Plants are particularly at
risk during the overwintering ( when most of the plants donít
tolerate temperature under 10įC) and some species proved to be
very problematic (Tavaresia spp., Hoodia spp., Larryleachia
(Trichocaulon) spp.) sometimes even during the growth season.
Prevention and cultural disease
control is the most important step in reducing this problem as
there is no an effective treatment, anyway when black rot
is seen at an early stage it is possible to try to recover the
plants removing and disposing carefully the affected parts and
placing the plant in quarantine.
Reduce water applications to any plants suspected of stem rot
disease and be sure to start with fresh potting medium, pots and
pathogen-free cuttings for each crop.