Understanding Plant Diseases

Crop production


Host: Have you noticed that the leaves on your crops are curling up or falling off? Or wondered why the grain isn’t forming properly on your maize or millet? It could be that some of your crops are infected with a disease.

Even if you don’t know the name of the disease that is damaging your plants, there are things you can do to stop it from getting worse. And, there are ways to stop your plants from getting diseases in the first place. These are the things that we’re going to talk about today.


Host: Here are a few facts about plant diseases.

Plant diseases are usually carried from one plant to another by insects or by the wind.

There are four major types of plant diseases. They are: fungi, bacteria, viruses, and nematodes.

All four types need several things in order to grow. They need food, a warm temperature, and moisture.


Host: Many diseases are most active when their surroundings are warm and damp. Knowing this, there are a few things you can do to prevent diseases from thriving on your crops.

For example, it’s important that plant leaves are able to dry out after a rain. This means that you shouldn’t plant crops too close together. It’s true that cereals such as millet or maize are usually planted closer together, but still, they shouldn’t be overcrowded. If your plants are crowded together and can’t dry out, diseases will spread more easily.

And, take care not to walk in your fields when the leaves are wet. When you walk among wet leaves, you can easily transfer disease from one plant to the next just by brushing against the leaves with your body.


Host: If you choose the best farm management practices possible, you protect your plants from disease. Certainly I think we can all agree that intercropping and crop rotation are two excellent farm practices. And they help with crop protection. If you have a variety of crops in your field, you’ll probably notice that you have fewer disease problems. Another thing to remember is that traditional crop varieties are often more tolerant than newly introduced varieties. So keep this in mind when deciding what to plant.


Host: Another good way to prevent a disease from infecting your crops is to wash your tools before you move from one crop to another. If you keep your tools clean, you will be less likely to carry the disease from plant to plant, or from field to field.


Host: If you see that your plants have a disease, take action to stop it from getting worse. Pick off the diseased parts of the plant. If the plant is really badly diseased, remove the whole thing, roots and all, from your field. Burn it, or bury it deeply in the soil.


Host: People need food to grow strong. So do plants. If your plants have enough nutrients from the soil, and enough water, they will grow strong. If they are strong they can avoid getting sick in the first place. What I’m saying is that even though there may be disease in the fields, or in the soil, your plants will have a better chance of staying healthy.


Host: As you can see, simple practices can help to prevent disease in your crops. And these are only a few examples. I’m sure many of you have other solutions. Once again, observation and experimentation – and time and patience – will give your plants a better chance to stay healthy and free of diseases.


  • Contributed by Jennifer Pittet, researcher/writer, Thornbury, Canada.
  • Adapted from Developing Countries Farm Radio Network Package 45, numbers 8 & 9, Understanding plant diseases – Part 1 and Part 2.
  • Reviewed by Hélène Chiasson, PhD, Codena inc., Saint-Charles-sur-Richelieu, Québec, Canada.

Information sources

  • “Developing a disease free garden.” Agriculture in action. Mar. 1990: 19-20. Barbados Agricultural Society, “The Grotto”, Beckles Road, St. Michael, Barbados, West Indies.
  • “How to avoid plant diseases.” Food gardens unlimited. Summer 95: 2-3. Food Gardens Foundation, PO Box 41250, Craighall, Johannesburg, 2024, South Africa.
  • Sherwood, Stephen, and Jeffery Bentley. “Rural farmers explore causes of plant disease.” ILEIA Newsletter. Mar. 1995: 20-22. Information Centre for Low-External-Input and Sustainable Agriculture (ILEIA), Kastanjelaan 5, PO Box 64, NL. 3830 AB Leusden, The Netherlands.
  • “Non-chemical methods to reduce disease infection on vegetables.” Insect and Disease Control in the Home Garden. 1979-80: 1-2. Ontario Ministry of Food, 1 Stone Road West, Guelph, Ontario, Canada. N1G 4Y2.
  • Agrios, George N. Plant pathology. New York: Academic Press, 1978.
  • de Guzman, Rebecca. What’s wrong with my plants? A guide to identifying plant diseases caused by pathogens (1987). International Rice Research Institute, PO Box 933, Manila 1099, Philippines.