Plant Pathology and Insect ID

Plant Diagnostics

The State’s Plant Pathology/Nematology Laboratory provides plant diagnostic services to the local agricultural industry and the general public. The laboratory is an important source of accurate, unbiased information on plant diseases caused by nematodes and other plant pathogens such as fungi, viruses, and bacteria.

The Department of Agriculture utilizes this service to survey for problems in nurseries and other farms to prevent widespread infestations of uncommon diseases or to meet requirements for exportation of agricultural products outside the county. 

Guidelines for Submitting a Plant Sample

  • The sample should be as fresh and complete as possible; with examples of soil, roots, stem, and leaves. When this is not possible, a picture may be helpful. 
  • The sample should be representative of the symptoms, in the diseased or dying stage but not completely dead. Once a plant has died, microorganisms that decay organic matter start to take hold, making it difficult to isolate what initially caused the plant's symptoms. 
  • The sample should not be too large or too small. Pieces the size of an arm's length or smaller can be worked on in the laboratory. When a sample consists of only a few leaves or pieces of bark, it is difficult to make good diagnosis. 
  • Samples should be taken before treatment with any pesticides. Pesticides prevent growth of insects and pathogens and may prevent us from finding the cause of the problem.
  • We ask that you bring the sample to our office early in the week so it doesn't sit in transit over the weekend. 

Processing time for determinations:

The average time for return of the diagnosis is 2-4 weeks. Individual samples may take more or less time, depending upon the pathogens involved and how busy the lab is.

Insect Identification: Collection and Sample Submission

The State’s Entomology Laboratory welcomes all submissions associated with the commercial production of an agricultural commodity. The Lab will also assist the pest control industry as staffing permits, as well as citizens with residential concerns. Please contact the County Health Department for help with insects of medical concern to pets and humans, as the lab does not handle these types of samples.

  • Collecting From the Garden: If insects are living on leaf tissue, snip a branch off of the plant that has insects present and immediately drop the specimen into a plastic zipper bag with air. If they are hopping insects, it is best to carefully place the plastic bag over the end of the branch first, close the bag and then cut the branch to prevent the insects from flying away once disturbed. 
  • Collecting from the Home: Insects should be delivered in a plastic zipper bag, jar, pill bottle or small plastic container. Attempt to collect multiple life stages of the insect and live collections are always preferable. Insect sticky traps maybe submitted but we ask that you avoid submitting samples on tape as this can increase the chances that the insect gets damaged which interferes with ID. 


Department of Ag Pest ID Services Handout (PDF)

Visit the University of California Integrated Pest Management Program website for more information on solving your pest problems: 

Justin Riggs

Agricultural Commissioner
Sealer of Weights and Measures
Animal Control Director
2650 W. Washington Blvd
Crescent City, CA 95531
Phone (707) 464-7235
Fax (707) 465-6044