High tunnel.

2016-17 Rapid Ag: Development of a Risk Assessment Model for Tomato Leaf Mold Infection in Minnesota

November 1, 2015

Principal Leader

Angela Orshinsky


Department of Plant Pathology

Funding Awarded

  • 2016 Fiscal Year: $77,079
  • 2017 Fiscal Year: $70,879 

The Problem

Tomato leaf mold is caused by fungus Passalora fulva and can lead to defoliation of tomato plants and fruit infectionThere is a critical need for current and precise epidemiological data that will assist in the development of recommendations to mitigate tomato leaf mold disease in MN high tunnels.


Consumer demand for local fruits and vegetables is growing in response to concerns over the food quality, food safety and environmental consequences of large-scale agriculture. Unfortunately, the growing season in Minnesota is too short to support the production of many fruits and vegetables, including tomatoes, without the use of high tunnels or greenhouses. High tunnels require little energy investment and lower capital costs than greenhouse systems. The implementation of regional, high tunnel food production has been assisted by the USDA Natural Resources Conservation Service. Minnesota is a national leader in high tunnel use for local food production with over 1500 tunnels in production. Tomatoes are the highest value high tunnel crop. Consequently, many growers plant tomatoes every year with little or no rotation of crop. It is estimated that each 2100 sq ft high tunnel can provide each grower with an average income of $12,000. Thus, tomato production is a substantial part of many small grower incomes and contributes up to an estimated $18,000,000 to Minnesota’s economy each year.

Tomato leaf mold is caused by the fungus, Passalora fulva (syn. Cladosporium fulvum, Fulvia fulva). Severe symptoms of tomato leaf mold disease include defoliation of tomato plants and fruit infection. P. fulva is typically a pathogen in southern climates where the humidity and dew points that promote infection and sporulation frequently occur. The disease has been studied at the molecular level for years as a model system for fungal elicitors of plant disease. However, there is limited applied research on management and the epidemiology of P. fulva. We do not know which pathogen races exist in Minnesota and the USA, the overwintering abilities of P. fulva in MN high tunnels, and potential for P. fulva to cause disease in field tomatoes under various climate models. This creates difficulty for Extension specialists and educators trying to give growers reliable recommendations. The research proposed here will address this critical need for current and precise epidemiological data that will assist in the development of recommendations to mitigate tomato leaf mold disease in MN high tunnels. The economic importance of tomato leaf mold has not been specifically studied; however, each three pound loss in yield at low market prices can reduce profits by over $2,000. At higher market prices, a 3 lb/plant loss in yield can result in over $4,000 loss per year per tunnel. Tomato leaf mold causes severe defoliation of tomato plants, which reduces yields due to loss of photosynthetic area. Fruit infection also occurs in severe outbreaks, rendering the fruit unmarketable. Reducing the severity of leaf mold in high tunnels will increase the profits with only hundreds of dollars invested in time and fungicide costs. The risk assessment model will allow us to develop fungicide timing recommendations that will maximize this small investment.


  1. Define the biological and environmental parameters for growth, sporulation, and survival required to produce a risk assessment model.

  2. Use parameters defined in objective 1 with CLIMEX/DYMEX software to develop a risk model for the tomato leaf mold pathogen in Minnesota high tunnel operations.

  3. Validate the risk model developed in objective 2 through collection of regional climate and high tunnel microclimate data and by monitoring disease progression at multiple high tunnel locations.

  4. Develop recommendations for fungicide (organic and conventional) selection and timing and share these recommendations with growers to reduce the impact of tomato leaf mold in Minnesota.

Angela Orshinsky.

Angela Orshinsky inspecting tomato plants being grown in a high tunnel environment.