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Diagnosing Horticultural Plant Problems

Fact Sheet PP-48
Nancy F Gregory, Plant Diagnostician
Brian Kunkel, IPM Specialist
Revised: 1/5/2012

Diagnosing horticultural plant problems is similar to being a detective. The investigator must collect and evaluate all clues, keep good notes, establish the facts, and synthesize them into a conclusion. Take adequate representative samples and keep collected samples in good condition. Have an open mind and don’t assume that the current problem is the same as another similar one. Damage may be more severe when multiple causal agents or stresses are involved. Clues to the problem are either signs or symptoms. Symptoms are the reactions or alterations of a plant as a result of a disease or insect. A sign is the pathogen or pest itself, or its products observed on a host (infected/infested) plant. A hand lens or microscope may be necessary to see some signs. There may be patterns of symptoms in a landscape or planting. By categorizing symptoms and signs and then using a key, the investigator can narrow the possible causes. The following key is a general example, and contains only a partial listing of potential causes of some symptoms. Follow up by packaging your sample and submitting it to your county Extension office or the UD Plant Diagnostic Clinic along with a completed sample submission form. Some samples require incubation in a moist environment or further testing for accurate diagnosis.

SYMPTOM AND SIGN KEY:

I. ENTIRE PLANT AFFECTED

II. BRANCHES OR PORTIONS OF PLANT AFFECTED

III. LEAF OR NEEDLE SYMPTOMS (COLOR)

IV. PHYSICAL DAMAGE TO LEAF OR NEEDLE (FEEDING)

V. CONSPICUOUS ABNORMAL GROWTHS

VI. PHYSICAL DAMAGE TO STEM OR BRANCH

VII. DISTORTION OR DAMAGE TO FLOWERS OR BUDS

VIII. DAMAGE TO FRUIT

IX. PHYSICAL DAMAGE TO BARK

Acknowledgement:
This fact sheet was originally developed using information from Derby Walker, Jr. and Dr. Dale Bray, and revised in 1998 by R. P. Mulrooney. Any reference to trade names is for information only and does not imply endorsement.

 

Disclaimer: Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension or bias against those not mentioned.