Holly Shrub Pest - Knowledgebase Question

Bel Air, Ma
Question by ciconroy
June 30, 2010
I think my holly shrub hedge is having a pest problem. We had an exceptionally snowy winter, in spring there were sticky, black areas. I fertilized with Holly Tone and srayed them with a mixture of water and Palmolive dish liquid. They were better but now I am noticing white oblong markings on the backs of the leaves. Should I treat them and if so, is there a natural way to do so?

Answer from NGA
June 30, 2010


You?re dealing with two separate problems with your holly. The black stuff is sooty molds and is the result of insect feeding. Aphids or scale insects feed by sucking the plant juices. They excrete a sticky called honeydew. The sugar content of this excrement is just high enough to encourage fungal growth which is the black coating on the surface of the leaves. Controlling the insects, which you probably did with your soap spray will stop the formation of sooty mold and it will eventually weather away. The tunneling you?re seeing in the leaves is the result of leaf miner insects. These are the larvae of a wasp or fly. The adult lays an egg by making a slit in the outer covering of the leaf. The egg hatches into a larvae which feeds between the upper and lower leaf surfaces. That?s what causes the squiggly lines in the leaves. You can?t really control these pests because they are protected within the leaves. Just cut off the affected leaves if you don?t like looking at them. Leafminers are worse some years than others and their feeding doesn?t really harm the plant so I tend to simply put up with them.
Good luck with your landscape.

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