Landscape - Diagnostic Tools and Resources

The following is a continuation on our series on diagnosing landscape problems with information on tools and resources available.

Basic diagnostic tools:

>Scissors, pruning shears, or a sharp knife to collect samples and observe internal symptoms.
>A hand lens for observing pathogen structures.
>A small, clear glass of water to check for signs of bacteria.
>Clean sandwich bags, ziplock bags, paper towels and rubber bands or twist ties for collecting and incubating samples.
>Some reference books. Several reference books are available for home use, but for detailed pathogen diagnosis, the most complete references are the disease Compendia published by the American Phytopathological Society (APS) Press. Individual compendia are available for specific crops or types of crops (e.g., stone fruits, cucurbits, turf grass, etc.). These compendia provide detailed descriptions of disease symptoms as well as descriptions of the pathogens causing the disease. The APS bookstore can be accessed at http://www.shopapspress.org/

Step-by-step procedures:

>Identify the plant(s) involved.
>Inquire into site history of plant disease or other problems.
>Look for patterns of symptoms on plant parts or whole plants.
>Assess spatial distribution of disease symptoms in the landscape.
>Examine disease symptoms and disease signs using a hand lens when necessary.
>Compare disease symptoms and signs to the images in reference books and those posted on the Internet.
>Perform simple examinations for potential bacterial and nematode diseases with the aid of basic tools listed above.
>Consult with a local Extension agent, then a professional diagnostician, if necessary, or send a sample to a public or private diagnostic lab, depending on the nature of the diseases to be examined.

Resources for Diagnostic Help

Land grant university-based disease diagnostic clinics, along with state agricultural (Cooperative) extension offices, usually provide timely and quality diagnostic service at no charge or for a small fee. However, these public labs are restricted in capacity due to limited financial support. They are often overloaded with disease samples, particularly in the summer. Diagnoses of some samples, such as viral diseases, may fall outside the scope of an individual lab. As a result, private diagnostic services are emerging.

The University of Delaware has a plant diagnostic clinic. Horticultural agents are available in each county extension office for initial consultation. Samples should be brought to the county offices in Georgetown, Dover, or Newark. If necessary, samples will be sent to our diagnostic lab. For routine testing there is no fee. The website for the plant diagnostic clinic at UD is http://ag.udel.edu/extension/pdc/index.htm

There are two types of private services. Some companies provide both diagnostic kits and direct diagnostic services; others provide only direct diagnostic services. These services are particularly valuable for virus testing. These private services are important alternative resources to help meet your plant disease diagnostic needs. For assistance in choosing a diagnostic lab, contact your county horticultural agent.

Extracted and modified from "A Guide to Diagnosing Diseases of Landscape Plants" by Chuan Hong, Extension Specialist; Tom Banko, Associate Professor; and Marcia Stefani, Research Specialist; Virginia Tech. For the full factsheet go to http://www.ext.vt.edu/pubs/plantdiseasefs/450-800/450-800.html