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By Thomas Butzler
Penn State Cooperative Extension - Clinton County

Are you just getting into the business?

Do you have the right “tools” to assist in diagnosing plant problems?

Looking to expand your company’s library?

There are many references in the industry that deal with pest problems in the landscape and nursery. I would like to concentrate on plant disease problems and those references that I have found useful in diagnosing plant diseases in my capacity as an IPM/Horticulture agent for Penn State Cooperative Extension Service. I will only be commenting on books and manuals. Internet references to plant diseases are plentiful and warrant another article in the future.

One reminder…these references are useless without knowledge of the plant material at hand. If you are having trouble with species identification, a good place to start is Michael Dirr’s Manual of Woody Landscape Plants. Once a plant is correctly identified one can move onto common diseases for the species listed in Dirr’s manual. Under each plant species is a paragraph that lists potential pest problems. Although not comprehensive, it will give you some clues about what plant disease problems are common for that particular plant.

Many people find The Ortho Problem Solver a useful reference. I have seen it especially useful in retail settings with customers waiting in line to thumb through the pages. One of the reasons I think this book is used so much is its excellent visual references that can be used to correctly identify plant problems. This hardback book contains over 1,000 pages of photos, lists, and easy-to-understand narratives. One word of caution; the solutions to problems usually involves one of Ortho’s own products. I would use this reference as a starting point and go elsewhere for additional information, especially control options.

Another useful book is Diseases of Trees and Shrubs by Sinclair, Lyon and Johnson. This book and the above mentioned Ortho Problem Solver and Manual of Woody Landscape Plants are great for IPM in the green industry. If you can’t use these books to help identify plant disease problems they can always be used to smash those pesky insects in the landscape. These books are heavy! Whereas The Ortho Problem Solver can be very easy to use for both the consumer and professional, Diseases of Trees and Shrubs is definitely for the professional as it is very detailed. With 247 pages of color plates (1,700 illustrations of diseases and injuries) and comprehensive text, this is a handy diagnostic aid that uses specific signs and symptoms on plant parts or entire plants to identify the disease-causing agent of an infected plant. In addition, there is some biological and control information for each disease problem.

The American Phytopathological Society (APS) publishes a series of compendia of plant diseases. These soft cover books are useful for assisting one in identification, control and prevention of diseases in crops. Most range in length for 70 to 110 pages, and all have many excellent color photographs of disease symptoms, as well as descriptions of the symptoms, life cycles of the pathogen, causes of disease and useful control methods. Of particular interest to landscapers and nursery workers are the compendia on: Flowering Potted Plant Diseases; Elm Diseases, Conifer Diseases, Ornamental Foliage Plant Diseases, Turfgrass Diseases, Rose Diseases, Chrysanthemum Diseases, Rhododendron and Azalea Diseases. See www.shopapspress.org or call 1-800-328-7560 to order APS publications

All of the above references do a great job in assisting professionals in identifying plant diseases. The one factor that is missing in those references is specific (for your area) up-to-date control measures. Penn State’s College of Agricultural Sciences Woody Ornamental Insect, Mite, and Disease Management Guide is a publication that is updated regularly for Pennsylvania’s green industry professionals. (Available for 7.00 dollars from Penn State, 1-877-345-0691; ask for AGRS-25) This 86-page guide summarizes insect, mite, and disease management practices for woody ornamentals and shade trees. It briefly lists the symptoms of the disease and as a result, may not be the best tool in diagnosing a disease problem. If you want more in-depth information on the diseases or pathogen, Penn States’ guide links you to Diseases of Trees and Shrubs by referring to the appropriate page number in this publication. The benefit of this guide for industry professionals in or around Pennsylvania is its specificity for Pennsylvania landscapers and nurserymen. This document is state or at least region (northeast) specific. Most states have something similar. For example, landscapers in Colorado may not find the Penn State publication as useful as Colorado State’s Insects and Diseases of Woody Plants in the Central Rockies. Note that the compendia’s, Diseases of Trees and Shrubs, and the Ortho Problem Solver cover a much wider geographic region, the Americas.

And if you are really stumped, call your local cooperative extension office. Chances are the extension agent has seen the problem before and can quickly diagnose the problem or can send the material off to a state specialist for an opinion.

Note: An excellent source for many of the publications described in this article, and more, is American Nurseryman Publishing. Call 1-800-621-5727 or go to: www.amerinursery.com

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