Plant Disease Management

Disease Management Pic

Yesterday, I shared what I learned in the Integrated Pest Management (IPM) class at the 2014 Carolina Yard Gardening School. During that class, the instructor also discussed plant disease management using IPM principles. That is today’s lesson.


If these three things occur at the same time, there will be plant disease:

  • A susceptible host – Certain diseases attack certain plants.
  • A virulent pathogen – A pathogen must be present in sufficient quantity to attack the plant.
  • A conducive environment – The environment must be right for the pathogen to survive and/or reproduce. (Example: high humidity, high temperature, wet conditions, etc.)

The key to plant disease management is to alter at least one of those three items in order to stop the disease cycle.

As we learned yesterday, IPM utilizes three management types to control garden pests; disease management utilizes two of them.

  • Cultural – what humans can do
  • Chemical


Plant diseases fall under the following categories:

  • Fungi
  • Oomycetes (responsible for “damping off” by causing knobby roots in wet soil)
  • Bacteria
  • Viruses
  • Viroids
  • Phytoplasmas
  • Protozoans


Here’s a list of many common plant diseases (though the list is not all-inclusive):

  • Gray mold
  • Powdery mildew
  • Downy mildew
  • Anthracnose
  • Damping off
  • Southern Stem blight (or other blights)
  • Bacterial wilt
  • Septoria leaf spot


Cultural controls affect the choice of plant and the environmental conditions in the garden.

  • Choose resistant varieties of plants (Hybrids are bred to be resistant to certain bacteria or viruses.)
  • Try grafted tomatoes or watermelons. The variety you want (even heirloom varieties) are grafted onto disease resistant roots.
  • Prune plants to keep them “open” so air can flow freely around all branches.
  • .Use drip irrigation, if possible. If it’s not, then stoop and water close to the soil. NEVER water from overhead.
  • Keep soil moist, not wet.
  • Rotate your crops each season.
  • Maintain sanitary conditions in your garden. Prune dead or diseased branches or leaves; deadhead flowers; remove crop debris.
  • Do not compost diseased plant debris; get rid of it.
  • Mulch your garden. Many fungi (like Septoria Leaf Spot) reside in the soil and will splash onto the bottom of your plants, causing disease.
  • Don’t over-fertilize. Excessive nitrogen increases disease pressure; rapid growth turns off disease fighting in plants. Your plants will tell you if they need nitrogen. (The older leaves will start turning yellow.)
  • Harvest fruit when ripe. Don’t let ripe fruit stay on the vine too long.
  • Continue to feed and water dormant perennials. Even dormant plants need food and energy to remain healthy.


The only chemical controls we can use on plant diseases are fungicides. If a fungicide is necessary, use a “soft” or organic product and follow these recommendations:

  • Know the disease you’re spraying for.
  • Read the chemical label well and follow instructions.
  • Spray early, as a preventative, before the disease develops. (If your plants get a disease you’re not familiar with – and didn’t prepare for – contact your local university extension for help in identifying the disease and learning ways to treat it.)
  • Rotate chemicals. Don’t use the same main ingredient over and over.

Last year, I had Septoria Leaf Spot on my tomatoes, both downy and powdery mildew on my cucumbers, and powdery mildew on my squash. I did use copper fungicide on my tomatoes, and it was helpful to an extent; but it would’ve been better had I prepared ahead of time. With our very hot and very humid summers, the environment is very conducive to disease. Because of this class, I’ll be better prepared this year to take more control of the environment of my garden and, hopefully, reduce disease on my plants.



What plant diseases do you battle in your garden?




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