Plant Pathology


A customer came into a nursery to ask what was the problem with his plant.  He was holding a dried-up dead (unidentifiable) perennial with bits of roots dangling below.  I had no clue.

Diagnosing plant diseases can be particularly challenging, unless there is an obvious symptom or sign.  A learning the difference between the two is equally important, and not always simple to do. 

  • A symptom is a reaction as a result of a disease, like wilting, galls, chlorosis (yellowing tissue), dieback, blotches, etc.  It is a change in the plant’s growth or exterior in response to a living (or non-living, such as extreme weather) destructive factor. 
  • A sign is the pathogen or its parts visible on the host plant, like a fruiting body, bacterial ooze, slime, or other yucky looking things!  It is direct proof of a damaging factor.

Understanding the difference between a symptom and a sign can help you arrive to a potential identification of the disease or problem, the cause, and how to prevent it in the future.

In December during a walk along a river, I spotted some wild flower stalks with odd round balls about half way down the center.  My husband accompanying me on the walk thought they were part of the plant and found them interesting.  Since we were collecting dried flower and cones for upcoming holiday container garden arrangements, I happen to have a pair of pruning shears with me.  Cutting open the ball revealed a quick learning opportunity for my husband.  Inside was a little tiny single insect surrounded by soft papery-like tissue from the plant’s reaction to insect’s home.  The round expansion on the stem was actually a gall.  A symptom.

A symptom

In October during our trip to Hawaii, I saw, for the first time, dodder on plants.  I learned about dodder last season during my master gardener classes.  Although these parasitic plants can a problem in CT, I’ve never seen or heard of it before.  However, on the Big Island of Hawai’i, it was visible on plants in many places during our travels.  A sign. 

Determining disease causes is not my favorite part of horticulture.  After all, it makes plants look out of character.  But learning about plant diseases is a necessity in this business.  Let’s face it.  Plant diseases are not normal thus they are not much fun to look at, but they must be addressed to improve the health of your garden, and the health of the gardener’s pride!

There are some common problems, like powdery mildew or downy mildew.  But even those can be uncommon to the general homeowner.  A woman’s reaction once when I told her she had powdery mildew on her plant was curious.  She backed away slowly, and said, “What the heck is that?!”  I felt useful during that conversation as I assured her it wasn’t contagious to humans. Then we discussed a plan of action, how to dispose of the plant properly, and plant varieties with resistant or tolerant traits.

Because of our very snowy season in CT, I suspect – as you may as well, we are going to have a very wet spring.  Moisture can be a big attributing factor to speeding up some disease problems.  Another big factor is temperature.  Both persuade the disease bad guys (organisms) to take action.  Timing is everything too.  Some diseases occur only during certain times of the season or year, and on specific plants. 

Repeat Snow

During plant studies, students learn about the big three needed for diseases to set it.  They are a “favorable environment” (like the extreme wetness soon to come), “susceptible host” (a plant that gets the disease easily), and a pathogen (the bad guy that causes the disease).  Without all three, your chances of disease incidences are greatly reduced.  Since we can’t control Mother Nature (as we CT folks were reminded the past couple months), we need to focus on the other two elements:  the plants we select and how we manage them. 

When you shop at your local nursery or consult with your professional designer this spring, like moi – Cathy T, ask about resistant varieties.  Think about things such as how to provide good air circulation around your plants and in your gardens, which products to use to amend your soil for proper drainage, and start off with the right plant in the right place.  Watch out for waterlogged places which can affect roots.

If you left a mess in your garden before winter, such as old debris and things that will remain wet, start to move them out early.  And start to consider what is normal or abnormal.  When my husband saw the galls on the wild flower stem, he thought it may be a seedpod.  It was not – it was abnormal. 

And other times, you just need to wait.  If a plant has winter injury, it may look awful at first, but it may also come back slowly.  As I said, diagnosing plant diseases can be a challenge.  Determining the problem, looking for patterns, plants affected, and gathering clues will be helpful if you go to a specialist for advice.  Be Inspector Clueso first.  Take note of things around the plant.

A book I found useful this year, introduced to me by my master gardener coordinator is, “What’s Wrong with My Plant? (And How do I Fix It?),” by David Deardorff and Kathryn Wadsworth.  I also like “The Ortho Problem Solver” manual for its images and description of plant problems, not necessarily the chemical application suggestions – but for determining what is wrong with the plant. 

But should you not want to look things up on your own, as my client, you can come to me, Cathy T.  I’ll do my best to help you this spring!

3 thoughts on “Plant Pathology

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