A pathogen is any organism that can cause a disease to develop in plant specimens. Some pathogens only affect a single host plant, while others affect a wide range of host plants. Fungi, bacteria, and viruses are some examples of pathogens.
There are several factors needed for disease to develop. First you need a pathogen, which is the organism that causes a disease to develop. You need a susceptible host plant. Favorable environmental conditions are needed for the pathogen to be active, such as wet, humid weather. Finally, time is needed for all of the factors to create the perfect storm in fields full of plants.
Examples of disease caused by fungi include black shank in tobacco. Black shank is caused by soil born fungi and even though growers take precautions by preventive measures such as fumigating, cultivar selection based on levels of resistance, and crop rotation sometimes still isn’t enough to ward off the fungi organisms becoming active during ideal conditions for them to become active. Frogeye Leaf Spot in soybeans is caused by fungi. The options for a crop to prevent this disease includes planting resistant cultivars with seed treatment, crop rotation, and making fungicide applications to protect the plants as they mature.
Bacteria causing disease in crops include granville wilt in tobacco. The bacteria organisms live in the soil and if conditions are favorable the bacteria can enter the plant through the root system. Management factors that can be used to reduce the occurrence include resistant cultivar selection, crop rotation, and fumigation.
An example of virus causing disease in crops is tobacco mosaic virus that affects tobacco and a few vegetable crops. Mosaic can cause a molted appearance in the foliage where you have a mix of dark and light green leaf tissue. Prevention of mosaic includes crop rotation and planting resistant cultivars.
As you have read in this article, disease is an afterthought to the pathogens that cause the disease to occur. For disease to occur the pathogen has to be present, along with a host plant, favorable environmental conditions, and timing. Even though growers can take management actions to attempt prevention of disease from developing, sometimes is still unsuccessful.
Della King is an extension agent with the Sampson County Cooperation Center specializing in Field Crops.