Black on Apples - Knowledgebase Question

Woodstock, Ge
Question by newcombr07
February 11, 2011
I have three apple trees. Last year while they were still on the tree, they were covered with a black coating. It would not all rub off. What cases this? What can I do to prevent this from happening this year. Thank you.

Answer from NGA
February 11, 2011


If the apples were a standard size and shape, I suspect the black coating was sooty mold. Sooty mold is caused by insect feeding - usually aphids or scale insects. Scales suck the plant juices and excrete a liquid called honeydew. The sugar content of this excrement is just high enough to encourage fungal growth. That's what you're seeing on the surface of the apples. There are several control options: if the plant isn't too large, you can use a gloved hand and squish the adult scales. Or you can scrub the scales off with a soft brush, then rinse with soapy water. Or, you can apply a dormant oil in February to effectively suffocate the scale insects. Apply dormant (horticultural) oil to all surfaces of the plant to get good control and don't spray if the air temperature is below 40F or above 65F. Be sure to read the label, and apply exactly according to directions to avoid damage to apple tree.

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