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Collecting Samples for Diagnostic Clinics

December 14, 2011

Properly identifying plant disorders is an important aspect of crop production.  Growers must first determine whether a problem even exists.  Some plant cultivars may naturally exhibit peculiar characteristics, such as ‘puckered’ leaves or have unusual colorations which may, in fact, be normal for that plant.  If an abnormality does exist, it is important to try to identify its cause (environment, disease, insect, nutrition, etc.).   Without the correct identity, a grower may implement a control strategy which is both ineffective and perhaps costly.  

Diagnostic clinics are frequently utilized to properly identify insect and disease organisms or to examine the nutrient concentrations within the growing media, plant tissues, and water samples.

The type of sample to submit varies by the type of results (for example nutritional status versus plant pathogen) being sought.  Regardless, it is important to submit the proper sample to the appropriate diagnostic clinic to obtain the desired results.  The following are guidelines to use when submitting samples to diagnostic clinics.

  1. Provide as much background information as possible.  Use the clinics submission form or at the very least include: the plant’s scientific name, common name, variety, its age, the growing conditions, any fertilizers and chemicals applied to the crop, when the problem first occurred, how quickly it developed, and any relevant observations depicting why you are submitting the sample.
  2. When possible submit the entire plant or representative samples from all of the plant parts (leaves, stems, and roots).  Submitting only symptomatic plant tissues could lead to an improper diagnosis as these samples may not be the cause of the problem.  It may also be beneficial to submit a soil sample for analysis.
  3. Submit quality samples.  Submitting inadequate samples may lead to an improper diagnosis or none at all. 
  4. Do not submit dead plant tissue to the laboratory.  Dead tissues often contain an abundance of saprophytic pathogens making it nearly impossible for a diagnostician to determine the original cause of plant death.
  5. Submit Multiple Samples.  Include samples showing various degrees of symptoms, perhaps one just beginning to show signs of the problem and one with symptoms that are obvious and can clearly be seen.  Make sure each sample sent is clearly labeled and identified.
  6. Submitting Leaf Samples.  Submit enough leaves (at least 10) to demonstrate the various ranges of disease symptoms, from early stages to older more advanced damage. Place the leaves a plastic bag containing a dry paper towel. Keep refrigerated until shipping.
  7. Submitting Stem Samples. Cut the stem below the point of injury to include some of the healthy stem tissue.  Place the stems wrapped in dry paper toweling into a plastic bag.  With stem related problems, it is also beneficial to submit samples of the roots as well.  Keep refrigerated until shipping.
  8. Submitting Root Samples.  Include enough soil to keep the roots moist during transit.  Place the root samples in a separate plastic bag from any stem samples being submitted.
  9. Submitting Samples With Insects or Mites.  Loosely wrap infested plant materials in paper towels and place them into a plastic bag that has small holes punched into it.  Keep refrigerated until shipping.
  10. Submitting Soft Bodied Insects. Place them in a non-breakable, water tight container containing 70% isopropyl alcohol.  Caterpillars, grubs, or worms should be placed in boiling water for 30 seconds prior to placing into the alcohol.
  11. Hard Bodied Insects Put them in a freezer for one or two days prior to submitting them to a laboratory for identification.  After they are frozen, gently wrap them in tissue paper and place them securely in a small box or vial.
  12. Send samples to diagnostic clinics early in the week.  Due to the nature of our business, it is recommended to send any samples overnight to the diagnostic clinic.  It typically takes 1 to 5 days, sometimes longer to reach a proper diagnosis.

With good sampling and background information, a proper diagnosis can generally be achieved.  However, in some instances, it may be necessary to resubmit the samples or to utilize more than one diagnostic clinic until a proper diagnosis can been achieved.

Be careful when interpreting any cultural recommendations given by a clinic; they specialize in diagnosing plant problems, not producing plants or managing cultural situations.  Always formulate your own solutions to cultural problems based on what is practical, effective, and economical.

Paul Pilon
Perennial Solutions Consulting


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