Are you concerned with a disease symptom in your field but do not know what it is?

Do you need assistance diagnosing a symptom?

Why is it Important to have Proper Identification of Plant Diseases?

Without proper identification, disease control efforts can be a waste of time and money if an incorrect approach is taken. Deploying disease control measures that are not suitable to manage the disease-causing agent could lead to further plant losses. Plant diseases are caused by infectious parasites such as nematodes, fungi, oomycetes, viruses, and bacteria. Various symptoms can be caused by a wide variety of organisms (Figure 1), because of this, proper identification of a pathogen is key to develop a management strategy.

Injury vs Disease

It is important to understand the difference between an injury and disease for plants. An injury occurs suddenly as a result of external force over a short period of time by mechanical, abiotic, or arthropod damage. Disease is harmful deviation from normal growth that is continuous and normally progressive. Examples of injury for a plant includes frost damage, insect damage, or damage caused by farm equipment. Whereas an example of disease damage can be a collapsed plant that has been slowly wilting due to a soil borne disease.

Figure 1. Schematic representation of basic functions of a plant on the left and interference with these functions caused by common types of plant pathogens shown on the right. Source: Agrios, G.N. 1997. Plant Pathology (4^th ed.).

The Disease Triangle

Plant disease is a dynamic and continuous process and involves interactions among the host, pathogen, and the environment over time. The host refers to the plant, the crop, or organism that harbors a pathogen. Disease occurs when the three main interactions from the disease triangle occur at the same time: a susceptible host, a virulent pathogen, and an environment favorable for disease development (Figure 2).

Figure 2. The plant disease triangle with the three necessary causal factors of disease positioned at the corners. Source: American Phytopathological Society.

Contact us for Disease Diagnosis

Pathogen identification is difficult to diagnose in the field and requires specialized equipment, protocols, and training for an accurate diagnosis.

If you suspect to have plant disease on your farm, contact the Small Farms team UCCE Hung Doan (Farm Advisor) or Natalie Solares (Community Educator Specialist) for support. For further information, please contact Natalie Solares at nasolare@ucanr.edu.

What to expect: Through an email, phone call or farm visit, the team can assess the situation to identify the next steps. As necessary, we will take plant samples from the symptomatic area, and submit them to the Vegetable and Strawberry pathology laboratory led by Dr. Alexander Putman at UC Riverside. Upon diagnosis, we will follow up with you. Detailed records of crop history, water applications, fertilizer applications, and important weather events that may have influenced the development of disease are useful and important to have available.

The author would like to thank Margaret G. Lloyd (UCCE Small Farms Advisor for Yolo, Sacramento, and Solano counties) for suggestions and proofreading the article.

Sources:

Plant disease management for Organic Crops. UC ANR Publication 7252

Francl, L. J. The Disease Triangle: a plant pathological paradigm revisited. American Phytopathological Society Teaching Notes.

Agrios, G.N. 1997. Plant Pathology (4^th ed.). Academic Press.