Hello from the Broomfield County Extension office and the Master Gardener Helpline.

Thank you for submitting your interesting question about your spirea bushes.

There are 2 insects which may damage your spirea: 1) Aphids which are tiny black insects that will suck the liquids from the leaves leaving the leaves curled, withering, and eventually dead. If you see aphids simply use a strong jet spray of water to remove the aphids and 2) spider mites, which are tiny yellowish insect which will leave silver dots, stippling on the leaves. Looking closer you may see delicate webbing. Treatment is to wash plant with strong jet spray of water or a horticultural oil, or neem oil. 

There is one fungus that may affect your spirea.: powdery mildew. Leaves will develop a fine white powder substance. Treatment is to reduce over spray with water during regular irrigation- water at base of plant and not foliage. Treat with a fungicide will reduce powdery mildew. 

From your description it appears the spirea has spider mites. I would recommend the strong jet spray of water followed by a horticultural oil if the problem persist.

Please call us at<personal data hidden> if you have further questions. I can also email us directly at BroomfieldMG@colostate edu.

Happy Gardening

Diann

From: askextension=<personal data hidden> <askextension=<personal data hidden>> on behalf of Ask Extension <<personal data hidden>>
Sent: Saturday, June 18, 2022 4:22 PM
To: CoopExt Broomfield MG <<personal data hidden>>
Subject: Question assigned to you (#0066273)