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Plant Pathology

Department of Plant Pathology


Diagnosis of Vegetable Diseases and Improved Disease Management

Diagnosis of Vegetable Diseases and Improved Disease Management

Rapid and accurate diagnosis of vegetable diseases benefits Ohio farmers by providing them with knowledge of the plant pathogens affecting their crops. New invasive species were identified and management approaches recommended.


Vegetable production in Ohio is diverse and robust, with production in Ohio over $6 million annually.  Cropping systems range from small-scale multi-crop hobby farms to some of the largest vegetable farms in the NE US, and include processing and fresh market vegetables and conventional and organic approaches.  Ohio vegetable crops are vulnerable to hundreds of economically damaging diseases, many of which are difficult to diagnose in the field, and require laboratory testing.  Accurate diagnosis of vegetable diseases is the first step in effective disease management.  Further, new and emerging diseases present additional diagnostic challenges.


The OSU Vegetable Pathology Lab, part of the Ohio Plant Diagnostic Network, used traditional and modern molecular techniques to diagnose eight vegetable diseases for the first time in Ohio in 2013.  Onion anthracnose was widespread over 75 acres of commercial bulb onions, weakening the plants and reducing yields. Black leaf mold, a new disease of tomatoes, was found in an Ohio vegetable garden.  Elements of a virus complex that robs garlic plants of vigor and reduces bulb size came from small farms specializing in local market sales. Bloat, a disease caused by a nematode, was also diagnosed for the first time in Ohio. Tomato chlorotic spot virus, an insect transmitted disease previously found only in Florida, affected tomatoes grown in high tunnels in the northern part of the state.  Lab pathologists researched management practices and communicated recommendations back to the growers and gardeners, as well as to the larger community through electronic and social media.


The OSU Vegetable Pathology Lab, working closely with OSU Extension, growers, consultants and gardeners in Ohio, diagnosed and provided management advice for more than 300 hundred cases in 2013.  Knowledge of the new diseases, in particular, was lacking among growers and gardeners.

Local and regional sharing or selling of garlic “seed” bulbs carrying unrecognized viruses and/or the bloat nematode contributed to the distribution of these diseases.  OSU vegetable pathologists identified existing strategies for management from regions where the diseases are known.  These included using virus-free garlic for planting, effective plant protectants and cultural practices for onion, and tomato seedling management strategies to prevent introduction of insect-transmitted virus diseases in tomatoes.

Disease management recommendations were distributed widely through VegNet ( to increase awareness and promote effective and environmentally sound management strategies.  For example, use of virus-free garlic cloves for planting can increase bulb diameter 200% and bulb weight up to 50% compared to garlic infected with one or more viruses.  Proper choice and timing of application of fungicides to bulb onions can control anthracnose and eliminate losses due to this disease.

These findings have implications beyond Ohio borders on the regional and national levels as these new diseases are likely to become established in other states where they are currently not known.

Sally Miller, Vegetable Pathology; Nancy Taylor, C. Wayne Ellett Plant and Pest Diagnostic Clinic