Plant Diagnosis: The Deceptive Nature of Symptoms

News Article

Happy New Year from the Plant and Insect Diagnostic Clinic staff!
 
This year has started with interesting samples that remind us of the importance of accurate diagnosis as the first step to making management decisions that will best resolve the problem.  Correct identification is a fundamental concept and the cornerstone of our integrated pest management extension and outreach activities.
 
The photos below show leaves of a spike plant submitted to the Clinic. The leaves had yellow discoloration that resembled a disease symptom (caused by an infectious agent or pathogen).  But upon closer examination, we observed spidermites (see picture below). The diagnosis of spider mites rather than fungal disease points to very different management recommendations.
 
Spider mites and pathogens do not have many similarities. Pathogens thrive in high humidity and use water droplets to splash from plant to plant. Mites are mobile and do not rely on water to move. Pathogens, in general, prefer specific kind of plants (i.e., they are usually host plant specific) while spider mites are not picky eaters (generalists).  Most importantly, management options that control mites and insects would not control plant pathogens, and vice-versa.
 
The Plant and Insect Diagnostic Clinic is here to help you. Proper diagnosis of what is wrong with your plant leads to effective and efficient pest management recommendations.

Yellow discoloration on spike plant leaves (Dracaena indivisa), top of the leaf
Yellow discoloration on spike plant leaves (Dracaena indivisa), top of the leaf.  Photo credit: Lina Rodriguez Salamanca, Plant and Insect Diagnostic Clinic.

Yellow discoloration on spike plant leaves (Dracaena indivisa), underside of the leaf.
Yellow discoloration on spike plant leaves (Dracaena indivisa), underside of the leaf.  Photo credit: Lina Rodriguez Salamanca, Plant and Insect Diagnostic Clinic.

spider mite on leaves of spike plants (Dracaena indivisa).
spider mite on leaves of spike plants (Dracaena indivisa). Photo credit: Lina Rodriguez Salamanca, Plant and Insect Diagnostic Clinic.

Category: 
Authors: 

Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician (Program Specialist II)

Dr. Lina Rodriguez Salamanca is an extension plant pathologist and diagnostician with the Iowa State University Plant and Insect Diagnostic Clinic, a member of the North Central Plant Diagnostic Network (NCPDN) and National Plant Diagnostic Netw...