Disease management tactics for vegetables

A prerecorded webinar on vegetable disease management tactics is now available at the Online IPM Academy website.

Successful disease management is achieved by accurately identifying the pathogen (causal agent of the symptoms), understanding the pathogen biology and the environment that affects its development. An integrated disease management plan should comprise tactics for disease prevention and once present, tactics that minimize disease spread in the greenhouse or the field.

Preventative management tactics are the best approach to manage diseases. Basic principles of disease management include avoidance, exclusion, use of resistant varieties, scouting and accurate pathogen diagnosis, and pathogen reduction. A combination of tactics within those principles can provide growers with the best disease management strategy.

Principles of plant disease management

Avoidance. Disease avoidance focuses on preventing the disease by selecting a field where there is no pathogen inoculum (structures or “seeds of the pathogen” such spores, sclerotia, etc.), or where the environment is not favorable for infection or disease development. Planting date is a common avoidance example; planting first in better drain soils or delaying planting until soils have warmed up can avoid certain soilborne diseases.

Exclusion. This principle uses tactics that prevent the introduction of the pathogens to the greenhouse or the field. Planting pathogen-free seed (for direct seeded crops) or pathogen-free transplants will reduce pathogen introduction to clean greenhouses or new fields.

Carefully inspect transplants once you have received them from your supplier. Look for symptoms and insect vectors. Management of insect vectors is also important in minimizing the spread of some viral diseases and insect damage.

Host resistance. Utilize varieties that are resistant or tolerant. This tactic is particularly useful in fields with history of disease and in cases where traits have been bred on commercial varieties. When looking at seed catalogs and websites, take a closer look at the features of the varieties and look for the words “resistant” or “tolerant.” It is important to understand the difference between those two terms.

When a variety is listed as resistant, it does not necessarily mean the variety is immune to a specific pathogen. It means the variety carries traits that delay the infection process or suppress disease development. Tolerance means that even though plants may become infected, they are capable of attainable yields. Local environment and weather can influence vegetable varieties performance. Review the “Midwest Vegetable Variety Trial Report” and examine the local performance of different varieties.

Detection and scouting. Scouting your plants frequently allows for early detection of symptomatic plants. To brush up on recognizing diseases on vegetable transplants, use the table and links in the article “Disease or disorder: How do I tell the difference? Part 2” by Michigan State University Extension.

Accurate pathogen identification. Remember, correct diagnosis is the first step to effective disease management. MSU Diagnostic Services specializes in diagnosing plant problems. The kind of pathogen diagnosed, such as fungi, watermold, bacteria or virus, will help determine what management tactics are appropriate to minimize yield losses.

Reduction. This tactic focuses on the reduction or elimination of the pathogen and its parts (inoculum or “seeds of the pathogen”). To reduce seed borne bacterial pathogen populations, use hot water and chlorine treatments on vegetable seeds. Sally Miller’s factsheets, “Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens” and “Hot Water Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens in Organic Production Systems,” will provide the steps necessary to treat seed properly for both conventional or organic production systems. Treatment is a function of time and chlorine concentration. Care must be taken to avoid seed damage. It would be best to practice on small seed lots and understand the procedure before moving into larger batches.

Managing irrigation can help keep fungal and bacterial disease development to a minimum and reduce pathogen spread in vegetable transplants.

A comprehensive weed management plan is important to control weeds that can be host of certain pathogens. Weeds in the nightshade family, for example hairy night shade, are known hosts for P. infestans, the pathogen responsible of late blight in tomatoes and potatoes.

Sanitation refers to any practice that eliminates or reduces the pathogen in the greenhouse or the field. Chopping and plowing under infected material and removing symptomatic and infected plants, leaves or debris from greenhouses and fields are common examples of sanitation. Tools and equipment sanitation prevents short and long distance spread of certain pathogens.

Crop rotation and biological control (antagonism, competition and parasites) can reduce the pathogen populations in the soil in the long run. The absence of a susceptible hosts for three or more years can impact the survival of available inoculum of certain pathogens in the soil.

Plant protection. This tactic aims to prevent infection and reduce pathogen spread and symptom development using chemical and physical barriers. Examples of physical barriers in the greenhouse include black plastic, weed barrier cloths or concrete-covered surfaces. In the field, plastic, mowed cover crop, straw or other mulches act as a physical barrier to prevent pathogens from being splashed in water droplets or pathogen-infested soil, ultimately preventing pathogen from splashing onto susceptible plant parts. To read about chemical barriers, see “Fungicides: Tools for vegetable disease management.”

Learn more about integrated pest management (IPM) at the Online IPM Academy website. Among the webinars MSU Extension is offering, the webinar titled “Tactics for vegetable disease management” is now available.

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