Great reference book for insects and diseases of woody plants

by Kristina Hughes

Gardening in the mountains is full of challenges, so I am always looking for reliable sources of horticultural information pertinent to our region and our specific issues (like this blog!). And it is especially important to have good information when trying to figure out what’s wrong with a struggling plant.

For the past two seasons I have been volunteering at the Jeffco Diagnostic Clinic where people bring us their sick plants for diagnosis. They also bring us insects they suspect might be doing evil in their landscapes, mysterious fungi that have appeared unbidden (often in mulch), and unfamiliar plants about whose identity clients are simply curious. We have to solve all kinds of garden and landscape problems.

We have an entire library of resource materials at the Clinic, including compendia of turf diseases and vegetable diseases, books large and small on almost every plant pathology subject. But I have found that there one which is my favorite. I don’t leave home without it (literally - I keep a copy in my car at all times). It’s easy to use and easy to understand. It’s geared specifically to problems in Colorado. I’ve been known to read it in my spare time because it’s so well organized and has such good pictures.....

It is ‘Insects and Diseases of Woody Plants in Colorado’ from CSU Extension, 2014 edition. It is a soft-cover, spiral-bound book of 322 pages and it cost $40 when I bought my copy several years ago.

It’s easier to use than any of the other books because in the back near the index there is a excellent key which directs the reader to the most likely culprits for any given plant.

Have you ever wondered why Ponderosa pines drop the tips of their branches periodically? If you looked in the back of this book, under ‘Pines’ there is a subsection for ‘Affecting trunk and larger branches’ and then a listing for ‘Chewing off twigs’ which directs you to read about Abert's squirrels on page 259. There you will find pictures of the types of damage squirrels can do to trees along with detailed information about which plants they damage, times of year damage is most likely to occur, life cycle of squirrels and recommendations for management. It is just enough detail for a layperson to be able to identify the problem and execute a solution confidently, without getting lost in overly technical jargon.

Spruce Gall Photo by Kristina

Have you seen this on a spruce? 

Or this on an aspen?

Poplar Twiggall Fly Photo by Utah State Extension

With this book, it’s easy to find out that the first one is Cooley Spruce Gall (page 140) and its mostly a cosmetic issue which usually doesn’t require intervention. The second one is caused by Poplar Twiggall Fly (page 141)which also doesn’t do much damage to the plant. 

This book addresses only problems of woody plants. But our woody plants are long-lived, important foundational elements in our landscapes and their loss can be devastating. This book contains a very broad range of information on insects, larger animal pests, bacteria, fungi, as well as non-living causes of disease, all organized in a highly accessible manner, which makes it easier for us to help our plants when they are struggling. I wish there were more books like this for other types of plants.

We have so many challenges in the mountains and having correct information allows us to be more effective when dealing with those challenges. I have found this book to be incredibly useful both in my personal gardening and in my various Master Gardener roles. It’s also just fun to read!

Kristina Hughes

Clear Creek County Master Gardener