I have mentioned all the rain we have had in the past few weeks here in Charleston. It has finally let up enough that I could really get out there and get some work done. I went to the back where all my Citrus are located, what I found was a little disturbing. It looks as if my Citrus have been fighting fires for the past week! They are covered in soot. I am pretty sure there have been no fires close to the plants and I know they quit smoking sometime last year. SO........
All kidding aside, they are covered in soot, but it has nothing to do with anything combustible. It is actually a sooty mold.
Sooty molds are dark fungi that grow on honeydew excreted by sucking insects, like Aphids, Mealybugs and Whiteflies. The latter being my problem. I thought I had gotten rid of the little white flying pains in the butt.
Sooty molds occur in all parts of North America. Capnodium citri is associated with Whiteflies and scale pests on citrus. There are other species of the mold that are associated with other pests on other plants. Basically they are all the same.
Honeydew is a sweet, clear, sticky substance secreted by the insects such as the Whiteflies. The honeydew drops from the insects to the leaves and twigs. Wind-blown sooty mold spores that stick to the honeydew then have a suitable medium for growth. Kind of like that jelly like stuff you played with in high school biology class. When the spores germinate, they send out black fungal strands that cover the plant tissue and cause the discoloration.
Although sooty molds do not infect plants, they can indirectly damage the plant by coating the leaves to the point that sunlight penetration is reduced or inhibited. Without adequate sunlight, the plant’s ability to carry on photosynthesis is reduced, which may stunt plant growth. When it can't produce food, it starves. Coated leaves may also prematurely die, causing leaf drop. Most plants will tolerate a small amount of coverage. Fruits or vegetables covered with sooty molds are edible. Simply remove the mold with a solution of mild soap and warm water. The mold itself can also be sprayed away or rubbed off with your finger.
As seen in these pictures:
Treating sooty mold is best done by treating the source of the problem first. Get rid of the sap sucking pests. If you don't, the mold will return. Luckily, there is a cure that will kill two pests with one spray. Horticultural oils. If one of the horticultural oils is used for control, it also has the advantage of helping to loosen the molds from the plant surface. This hastens the weathering away of the sooty molds. However, it may still linger on your plants for months, even after the pests have been eradicated. Horticultural oils are available at most garden centers and big box stores. There is one problem though, it can not be used in intense heat. The oil will basically do what oils do to food, cook it! Cooler weather, overcast days, or in the evening are the best times. PLEASE, make sure you follow the label directions!
Just as a side note, plants are not the only thing affected by sooty mold. If an object is under a tree or plant that has sap sucking insects present, it can be covered in the soot.
I got lucky, it was a cloudy, cooler weekend, so I sprayed my trees with Neem oil.
Sooty mold is not as bad as it looks, it can be a major problem, but with a little work, your plant will be fine......unless they take up smoking again!!