Scale insects on holly

Question ...

I have a holly tree, about 2m high, outside in a large pot. It is covered in scale insects and most of its leaves are now black with sooty mould. It has always been healthy and I have only just noticed how bad the problem has become. I had a bay tree next to it last year that became badly infested with scale which I managed to clean up by wiping them off a leaf at a time! It took ages but it worked. I can't do this with the holly as it's so big and the leaves are prickly. Suggestions please to save my holly.

Answer ...

Scale is often a problem on trees or shrubs growing in pots. The restricted growing conditions cause stress to the plants, and stressed plants succumb more rapidly to pest attack. Make sure your holly has sufficient food and water to help it survive, and to maintain its health. Top dress the potting compost each spring with garden compost or well-rotted and sieved manure. Fork in gently with a hand fork, taking care not to damage the roots. Make sure that the tree never goes short of water. Dry spells in winter particularly can put evergreens, such as bay and holly, under enormous stress. A leafmould mulch is an excellent way to retain moisture in the pot, and it improves the quality of the potting compost too.

To treat the scale, use a toothbrush to repeatedly brush them off. You can also spray with insecticidal soap. However, this has limited affect, and the best time to spray would be in June and July when the juvenile scales (known as crawlers) are on the move.

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