One of the most frequently asked of Master Gardeners is "What is damaging my tree?" The purpose of this collection of photos is to help Master Gardeners diagnose tree and shrub pest problems. Included are photos of typical damage and the agents that cause the damage: insects, parasitic plants, fungi, etc. These photos are accompanied by a minimum of written information. Included is information on common pests of trees and shrubs in a typical Colorado Front Range urban setting as well as pests common to adjacent urban/wildland interface areas. These photos are from a collection that has taken me over 40 years of working as a forest health specialist with USDA Forest Service, and, more recently, as a Master Gardener to accumulate.

This electronic version is the second edition of this guide. The first consisted of a single copy in a lose-leaf binder that resided in the library of the Larimer County Office of the Colorado State University Cooperative Extension Service. I hope this version will be more accessible to Larimer County Master Gardeners as well as Master Gardeners throughout Colorado and adjoining states. Please feel free to print pages from this guide as needed for field use.

To use this guide, please refer to the instructions in the section "How to Use this Guide."

I plan to add additional material over time and in this regard I may never actually finish this project. Hopefully, the information contained on these pages will be a significant help to my fellow Master Gardeners. Your comments and suggestions are always welcome.
 

To facilitate use of guide, the pests described are subdivided into the following sections:

* Bark beetles

* Stem and wood boring insects

* Shoot and twig borers

* Foliage feeding insects

* Sucking insects (aphids, scales, mealybugs, psyllids, spittlebugs).

* Gall insects

* Mites

* Parasitic plants

* Diseases caused by fungi

* Diseases caused by bacteria

* Conditions caused by a combination of factors

* Diseases caused by weather, nutrient deficiencies, exposure to chemicals or unknown causes.

Bark beetles are among Colorado’s most destructive forest pests. Outbreaks, capable of killing thousands of trees, are usually present somewhere in the state. Some species are capable of spreading tree diseases. Although most bark beetles are pests of forested and urban/wildland interface areas, some species can become serious pests in urban areas. The bark beetle described in this guide include:

The larval stage of several groups of insects, including beetles, wasps and moths can bore into the wood of healthy, weakened or recently killed trees. If healthy trees are attacked, they can weaken their structural integrity and make them more susceptible to windthrow. Insects described in this section are:

A number of insects attack the growing tips of trees and shrubs. Their damage includes reduced growth, poor form and the unsightly appearance of trees. Insects included in this section are:

A large number of insects feed on the foliage of trees and woody plants. Several species, such as western spruce budworm and Douglas-fir tussock moth are major forest pests. Other species are primarily pests or shade and ornamental trees. Foliage feeding insects included in this guide are:

Sucking insects are a large group with specialized mouthparts that allow them to suck plant juices. They often feed in colonies and are found on the shoots, foliage and stems of woody plants. Many sucking insects are important pests of trees and plants in urban environments. Sucking insects included in this guide are:

Some insects are capable of producing structures, known as galls, in which they produce their young. These galls are often unsightly and some can cause deformity and twig dieback on the plants they attack. Most insect galls have characteristics that permit the identification of the insect that caused the gall. Insects that produce galls include certain species of aphids, flies and wasps. Several are important pests of shade and ornamental plants. Gall insects included in this section are:

Mites are microscopic organisms closely related to insects. A number of mites of the family Eriophyidae can cause damage to plants. Some mites produce galls, others produce other types of deformities and still others produce a mottling or discoloration of the foliage. Mites included in this guide are:

Parasitic plants draw their nutrition from other plants. They can attach themselves to the roots, stems or branches of their hosts. Some parasitic plants can cause deformity, weakening and, eventually, death of their hosts. In Colorado and other western states, the dwarf mistletoes, Arceuthobium spp., are important parasitic plants of conifers and are considered major forest pests. Parasitic plants included in this guide are:

Fungi are among the most important causes of plant disease. These organisms can attack virtually every part of a plant. They can cause decay, destroy root systems and attack foliage, flowers and seeds. Many species of fungi are important pests of ornamental and shade trees. Included in this guide are:

Bacteria are another important cause of plant diseases. Several bacteria cause damage to shade ornamental and fruit trees. Bacterial diseases described in this guide include:

Some plant diseases are the result of two or more factors acting in combination. At least one disease in our area is the result of what is believed to be an interaction of two organisms:

Many plant diseases are caused by weather, lack of soil nutrients, exposure to chemical pollutants or, causes yet to be determined. Diseases not caused by a biotic agent, such as a parasitic plant, fungus, virus or bacterium, are often referred to as abiotic diseases. Several abiotoc conditions are common in our area. Those described in this guide include: