An Introduction to Plant Disease


The very definition of organic, "of living things," lends itself to something that has a life cycle; a beginning and an end. Plants, like any other organic matter, are susceptible to pathogens that can shorten their lifespan and degrade their time spent growing in our beautiful gardens.

Some plants are hardy, or resistant to plant disease. These are species that have developed certain immunities and resistances to invading pathogens. However, some plants are weak to the invasion of plant disease and lack a strong support system to fight against it.

Horticulturists identify diseases by their life cycles. The following outline of a plant disease life cycle displays the process of inoculation, growth and reproduction of a pathogen. It should be noted that a one-cycle plant disease, that is one that occurs only once during a growing cycle, is called monocylic; others that happen recurrently are called polycyclic.

The Plant Disease Cycle:

  • Pathogen comes into contact with susceptible host. This is called inoculation.
  • Enters host through a physical wound or natural openings such as stoma (plant pores)
  • Establishes a presence within the host
  • Grows and reproduces within its host environment
  • Following reproduction, pathogen is able to spread to other susceptible plants. This is called dissemination.
  • Process continues until pathogen life cycle ends or human intervention takes place

When plants become sick they start to exhibit symptoms of infection, just as we would if we were infected with a cold or flu virus.

General Symptoms of Plant Disease:

  • Abnormality in plant coloring: withering leaves turn yellow (Chlortic); dying leaves turn brown (necrotic); others may turn purple, bronze, or red.
  • Weakening of plant structure: Pathogens that interfere with the water uptake process cause a plant to wilt. Fungi that do this are Verticillium and Fusarium. As they colonize and fill the conductive tissue of a plant (xylem), they inhibit water uptake.
  • Defoliation is another concern as the plant becomes too weak to maintain its ability to perform photosynthesis.
  • Leaves, steams or roots can become necrotic, and the future outcome of an uncontrolled plant disease is most likely death. The necrosis (death) of plant tissue is obviously the most poignant result of plant disease.
    Anthracnose on peppers

Pathogens are the disease hosts and are responsible for causing the plant disease. Much like the flu virus is a pathogen that attacks our immune system, plants can be taken over by several types of pathogens as well.

Types of Plant Pathogens:
  • Viruses infect a plant via intracellular means, meaning inside the cell. They infect other cells and live off the nutrients of the specific host, in this case the plant.
  • Bacteria are microscopic single-celled prokaryotic organisms (cells without a nucleus) that reproduce by cell splitting, a process called binary fission.
  • Fungi are the largest cause of plant disease. They are eukaryotic organisms (cells with a nucleus) that may or may not produce reproductive spores.
  • Another type of plant pathogen is a multi-celled creature called the nematode that is worm-like in appearance. There are also parasitic plants, which are organisms that feed off of others to survive.

The best way to ensure that a plant has a healthy immune system is by giving it a regular dose of our exceptional plant nutrition and fungicide product, Emerald Mist. With a strong and healthy plant, pathogens will have a difficult time inoculating a plant. And with a boost of "good-guy" fungi, a natural defense system of beneficial cells will develop on the plants' roots thereby helping plants to fight against invading disease.

Contact Garden Vigor for information on our natural gardening products that promote vitality, strength and growth in all plants.