What Are the Different Types of Crop Diseases?

Rebecca Mecomber

Every year, agricultural producers lose vast quantities of crops to various crop diseases. To understand how and why certain diseases strike certain crops, plant pathologists have categorized all diseases into two general groups, infectious and non-infectious. Once segmented into one of the categories, diseases are then described by the characteristic of the offending pathogen or environmental cause, such as fungal, bacterial, extreme temperatures or soil deficiency. Finally, horticulturalists further classify a disease by the part of the crop that is affected, such as leaf diseases, root diseases and more. There are multitudes of different types of crop diseases, but all diseases basically fall under the category of infectious and non-infectious for further classification.

Agricultural producers lose valuable crops each year to disease.
Agricultural producers lose valuable crops each year to disease.

Non-infectious, or abiotic, diseases are those that are caused by unfavorable environmental circumstances and that do not result from living organisms. Generally, non-infectious diseases tend to weaken a plant, making the plant susceptible to the more serious infectious diseases. Examples of non-infectious diseases include extreme temperatures, excessive or lack of water, insects, poor soil nutrition content and toxic chemicals. These factors can weaken the entire plant or a certain part of the plant, making the plant susceptible to infectious stem diseases, seed diseases, pod diseases and more.

A fungus or bacterial blight can be the kiss of death for a farmer's crop.
A fungus or bacterial blight can be the kiss of death for a farmer's crop.

Infectious, or biotic, diseases make up the bulk of variety of crop diseases. These are caused by living organisms that infect the crop. Fungi, such as smuts, rusts, molds and blights, are the most common cause for crop diseases. Most fungi require very moist conditions in which to thrive and reproduce. Some fungi develop pustules on the crops, while others produce a colony of powdery, discolored soot.

The science of treating and curing crop diseases is highly important to the agriculture industry.
The science of treating and curing crop diseases is highly important to the agriculture industry.

Bacteria and viruses, which are other infectious hosts, are tiny organisms that infiltrate the plant organs and reproduce. Some bacteria do not harm crops, but others can produce toxins or attack the plants' cells for food. Viruses are usually spread by insects when an insect chews through the plant's protective outer layer and infiltrates the inner cells. Bacterial blights and wilts often plague wheat and barley crops as well as vegetables, such as cucumbers and beans. Crop diseases caused by viruses can cause considerable damage, such as wheat streak mosaic virus and potato virus diseases than can eradicate an entire crop very quickly.

Non-infectious diseases are caused by unfavorable environmental conditions, such as poor soil nutrition and excessive lack of water.
Non-infectious diseases are caused by unfavorable environmental conditions, such as poor soil nutrition and excessive lack of water.

Nematodes and protozoa are also classified as infectious diseases. These tiny worm-like organisms reside in the soil, waiting for an opportunity to attack a crop weakened by non-infectious causes. They may carry viruses, causing further damage to crops and complicating disease treatment. Examples of these biotic diseases include the potato cyst nematode, pine wilt and soybean cyst nematode. As ascertained from their names, these crop diseases invade the sensitive root or vascular systems of the crops and cause cysts that stunt plant growth and sharply decrease crop yields.

Curbing or curing crop diseases is big business. Scientists and agriculturalists have developed myriads of fungicides, insecticides, pesticides and antibacterial solutions for crop disease control. While advances have been made, pathogens have shown a tenacious propensity to adapt to repellants. As the agriculture industry learns more about the various types and causes of crop diseases it becomes better equipped to treat and prevent the many diseases that plague the world's crops.

Ringspot, which can cause circular lesions on plant leaves, is an example of a viral plant disease.
Ringspot, which can cause circular lesions on plant leaves, is an example of a viral plant disease.

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