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From the Hort Desk

By Lisa Mason, CSU Extension Horticulture Agent

Plant and Insect Diagnostics: Always Something New to Learn

My colleagues and I hosted a plant and insect diagnostic workshop in October, a collaboration with CSU Extension and the Plant Diagnostic Clinic at the CSU Spur campus in Denver. About 45 Extension staff and Colorado Master Gardener volunteers gathered to build relationships and learn more about plant pathology and insects. While I taught portions of the workshop, I am always humbled to remember the more I learn, the more I realize I don’t know.

For instance, I learned that we have a weedy species of bluegrass (Poa trivialis, rough bluegrass) that can be fairly common in lawns. When the weather heats up, this type of bluegrass goes dormant. The grass turns a slightly purple color before turning brown. This is a great reminder that it is so important to know the plant identification before solving the problem. Brown spots in lawns often are caused by gaps in the irrigation systems, but it’s worth identifying the grass species to see if it could be rough bluegrass. The solutions for irrigation gaps and removing a weedy species in the lawn are entirely different.

Overall, the biggest take-home message from the workshop was a reminder to understand the big picture of the plant in the landscape before making any judgements or diagnoses.

Diagnostic workshop participants examine insects in the Orthoptera order (grasshoppers, crickets, and katydids). Photo: Lisa Mason

What exactly are plant and insect diagnostics?

Extension offices around the state receive a broad spectrum of questions varying in topic, need, and complexity. Some examples of common questions include: How do I get a soil test? Is emerald ash borer in my county? What plants do you recommend for a xeriscape garden? Why do I have brown spots in my lawn? What disease does my tomato plant have? Why is my tree struggling? Are insects harming my plant?

Plant diagnostics requires an understanding of environmental context clues. In addition, signs and symptoms present on the plant must be considered. While this might sound easy, the process of diagnosing a plant issue can be very complicated! Consider when you go to the doctor for a medical diagnosis for a persistent fever. A wide variety of bacterial and viral infections, and other ailments could cause a fever. A doctor will ask you questions to understand the bigger picture and look for clues. Depending on the answers, the doctor may choose to run some tests. Test results will further inform a diagnosis. Plant diagnostics is similar. Perhaps you have a plant with brown leaves. Those brown leaves could be a symptom from a number of environmental factors like drought stress or root damage. Perhaps a bacterial, viral, or fungal pathogen is causing brown-colored leaves. In some cases, maybe insects could be causing the damage to the plant.

Three different causes of “brown leaves.” Left: Elm leafminer, a sawfly that feeds within elm leaves creating brown patches. Center: fire blight, a contagious bacterial disease affecting plants in the Rosaceae family. Right: Severe iron chlorosis, an abotic or environmental condition where the plant can’t take up iron from the soil. Photos: Lisa Mason, William Jacobi, CSU,, and University of Illinois Plant Clinic.

When you submit a plant or insect sample for diagnosis, be prepared to answer questions. Here are some of the most common questions you’ll be asked after you submit a plant sample:

  1. What do you need answered?
    • Identification
    • Diagnosis and management recommendations
    • Identification and control advice
    • Other
  2. Do you have photos of the plant? Please submit photos up close of the damage and also far away from the plant to see the entire plant in the landscape.
  3. Do you know the identification of the plant?
  4. Where is the plant growing? (e.g., raised bed, next to the house, in the lawn, etc.)
  5. How much water does the plant receive? How is the plant watered?
  6. Did you apply any products (fertilizer, pesticides, etc.) to the plant? What products and how often?
  7. Describe the issues and any observations you’ve noticed.
  8. What part of the plant is affected? (e.g., leaves, trunk, branches, fruit, etc.)
  9. When did you first notice the issue? Are nearby plants affected?
  10. Has anything changed in the environment recently?

The Extension Plant Clinic staff member or Master Gardener will likely have additional questions depending on if the plant sample is a tree, lawn, vegetable, other plant, or insect. All these questions help inform the next steps for diagnosis and management recommendations.

Where do I submit my plant sample?

You have options! CSU Extension and the Plant Diagnostic Clinic partner together to ensure you get an accurate identification and/or diagnosis. When you have a question or bring in a plant or insect sample to your local county Extension office, we make sure to find the right expert to identify and/or diagnose the issue. Depending on the nature of your question or sample, your question may be answered by Master Gardeners, Extension staff or specialists, or experts at the CSU Plant Diagnostic Clinic. Please note some local counties may have a fee and the CSU Plant Diagnostic Clinic charges a fee for samples. Ask your local county office if there is a fee. Click here for the CSU Plant Diagnostic Clinic fees.

In Arapahoe County, you can ask Master Gardeners or staff questions by emailing or calling the office at 303-730-1920. The Arapahoe County Extension office accepts samples at 6934 S. Lima St. Suite B. Centennial, CO 80112. Each sample has an $8 fee. Samples are accepted Monday through Thursday, 8:00 am-4:30 pm, April 15-October 15.

Learn more about plant and insects

Land grant universities like Colorado State University have a long history working on plant diagnostics (Iles et al., 2021). If you are interested in learning more about nationwide plant diagnostic efforts, check out the National Plant Diagnostic Network.

Challenges with plants can often be avoided with the right care practices. Learn more by taking classes through CSU Extension on variety of topics related to plants, insects, gardening, and more! Check your local county office, the free webinars on the Co-Horts Blog, or Green School which includes the Colorado Master Gardener program.

What is CSU Spur?

Have you heard of the brand new CSU Spur campus? If not, you’ll want to learn more! Spur is a brand-new campus located within the National Western Center in Denver. This campus is open to the public and is worth the visit to see the state-of-the-art research and education facility with art installations and exhibits on veterinary care, equine therapy and more. The CSU Plant Diagnostic Clinic is now open at Spur! This is the Colorado state lab in the National Plant Diagnostic Network. They offer services such as plant disease diagnosis, insect identification, plant identification, and recommendations. The Soil, Water, and Plant Testing Laboratory will also be opening at the Spur campus. Stay tuned for their opening date.

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