As a gardener, it can sometimes seem like nature is stacked against your successfully producing a vegetable crop. Insect pests attack plants, weather produces too much or not enough rain or sunshine and, to top things off, plants can become infected with diseases, much like people can. Luckily, plant diseases can be prevented by careful gardening practices that focus on maintaining plant health.
As the University of Missouri Extension's website points out, diseases are responses to environmental conditions or pathogens. The symptoms that the plant shows provide clues about how the disease affects the plant, as well as the plant's attempt to develop a natural response. A susceptible plant, a pathogen and an environment conducive to the disease state are all required for a disease to manifest.
Plant diseases are classified according to the pathogen that causes the disease. Fungi, bacteria, viruses and nematodes can all cause diseases in plants, with fungi the most common pathogens. Fungi damage plants by feeding on their living tissues, causing cankers, rots and wilts. Bacteria are single-celled organisms that infect and injure plant tissue. Just like humans, plants can acquire bacterial infections through wounds. Viruses are tiny particles that require a host cell to reproduce. Once inside the cell, they afflict the plant from within. Pathogenic nematodes are microscopic worms that drain plant cells of nutrients.
Accurate identification of plant diseases is important, according to the University of Missouri Extension's website, because it saves time and expense wasted on ineffective treatment. The extension recommends following five steps when attempting to diagnose a plant disease. First, identify the plant, learn how the plant normally appears or behaves and identify common diseases that affect it. Next, eliminate possible causes that aren't related to disease, such as too much or too little water, insect infestation or nutrient deficiency. Finally, carefully inspect the plant, precisely describing the symptoms and their location.
Plant diseases progress in a cycle, where environmental conditions allow for infection, which flourishes in the plant, multiplies itself and continues to reinfect the plant. Treatments interrupt the disease cycle at one of those points, such as preventing pathogenic bacteria from reproducing. Treatments may include the application of chemicals, such as fungicides or bactericides. Biological controls introduce organisms onto the plant that destroy the pathogen without harming the plant, such as fungi that produce antibiotics or bacteria that are natural hunters of pathogenic nematodes. In other cases, eliminating the environmental causes that make the plant susceptible will halt the disease, such as watering a garden in the morning to prevent pumpkin leaves from remaining wet overnight when they are highly susceptible to powdery mildew.
Just like people, plants under stress get sick more often. While environmental factors, like the weather, make constant maintenance of optimal conditions impossible, gardeners can take steps to ensure that plants receive adequate nutrients from the soil, appropriate amounts of water and sunlight and undergo minimal physical damage. Other gardening practices break the disease cycle. For example, crop rotation ensures that a single species will not occupy the same space in the garden, becoming susceptible to reinfection by soil-borne diseases the developed the previous year.