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What’s Wrong with My Tomatoes? Lesson 1: Buckeye Rot

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June 4, 2020


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Welcome to today’s lesson of “What’s wrong with my tomatoes”? I’m Rebecca Melanson, an Extension Plant Pathologist with the Mississippi State University Extension Service. Today, I’m going to talk to you about a disease commonly seen in tomatoes in Mississippi.

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Each year tomatoes are threatened by a number of diseases that have the ability to damage plants and reduce yields. In some areas, certain diseases are more problematic than others.

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The development of these diseases depends on the presence of a virulent pathogen, a susceptible host, and favorable environmental conditions. A specific disease develops when all three conditions for that disease are met.

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However, when one of the conditions for that disease is absent, that disease does not occur 

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This principle is called the Disease Triangle and is used to determine which disease management methods are suitable for each disease.

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Today’s lesson will discuss the disease buckeye rot in tomatoes.

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Buckeye rot is a disease of tomato fruits caused by oomycete species in the genus Phytophthora. Oomycetes are fungal-like organisms that may commonly be called water molds.

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The Phytophthora species that cause buckeye rot in tomatoes are present in the soil. These pathogens come in contact with susceptible fruits when contaminated soil is splashed onto fruits by rain or overhead irrigation. When favorable environmental conditions are present, these pathogens can infect both green and ripe fruits and cause disease. Prolonged periods of warm, wet weather support buckeye rot development.   

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Fruits that become infected are often low-hanging and close to the ground as these fruits are more likely to have soil splashed on them during rains or overhead watering. Buckeye rot lesions are brown and oily-looking with alternating light and dark concentric rings. These lesions can expand to cover much of the fruit surface. When favorable conditions are present, white, cottony pathogen growth may develop on infected fruit tissues.

Buckeye rot is sometimes confused with the disorder blossom-end rot as lesions often begin at the bottom or blossom-end of fruits. Blossom-end rot lesions begin as light brown lesions, but these lesions do not exhibit the alternating light and dark concentric rings typical of buckeye rot lesions.  Blossom-end rot lesions may eventually turn black and become sunken. Mold may also begin growing on the affected tissue. Blossom-end rot is not caused by a pathogen, but by a lack of calcium in the developing fruit.

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Buckeye rot in tomatoes can be managed by practicing a number of disease management methods. First, plant in well-drained soils. Choose a site that drains well or make modifications to the intended planting site that help to improve drainage.

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During and after the growing season, remove and discard infected fruits from plants and gardens. Leaving infected fruits in the garden allows the pathogens to continue to grow and increase in number. Eventually, these pathogens make their way back into the soil where they can persist into future growing seasons to infect susceptible hosts and cause disease when conditions are favorable. Tossing infected fruits into compost piles is not recommended. 

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Planting the same crop in the same field from season to season or planting hosts that can be infected by the same pathogen from season to season allows pathogens that can persist in the soil to build up in the soil.

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Rotating out of solanaceous crops, such as eggplants, peppers, potatoes, and tomatoes, can help to reduce the amount of inoculum present in the soil. This is important since species of Phytophthora that cause buckeye rot in tomatoes can also cause disease in other solanaceous crops.

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Staking or caging tomatoes and using mulch can also help reduce the occurrence of buckeye rot. Staking or caging plants helps to create distance between susceptible fruits and infested soil reducing the chance that the infested soil may reach fruits when rains or overhead watering causes splashing. Whereas staking and caging does not prevent or reduce splashing, mulch serves as a physical barrier between susceptible fruits and infested soil and can help prevent or reduce the splashing of soil onto susceptible fruits. 

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A number of fungicides are available for use in commercial tomato production and are labeled for use against buckeye rot. A list of these fungicides is available in the Southeastern U.S. Vegetable Crop Handbook.

There are, however, no home garden fungicides labeled for use against buckeye rot in tomatoes. For this reason, home gardeners will need to focus on the described non-chemical disease management methods.

Even when fungicides are available for use, a combination of disease management practices should be used to help manage disease. 

Remember, when using fungicides, be sure to completely read and follow all label instructions. The label is the law. 

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Thank you for joining me today to learn about buckeye rot in tomatoes. You can learn more about disease management methods in tomatoes and about other tomato diseases in the publication “Common Diseases of Tomatoes” available on the MSU Extension Service website at Also, follow the MSU Extension Diseases of Vegetables, Fruits, and Pecans Facebook page for future updates on various plant diseases. Have a great day and happy growing! 

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The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.

This video is partially supported by Crop Protection and Pest Management, Extension Implementation Program grant no. 2017-70006-27200/project accession no. 1014037 from the USDA National Institute of Food and Agriculture.  Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Produced by Rebecca A. Melanson, Ph.D. (June 2020).

Copyright 2020 by Mississippi State University. All rights reserved. This video may be copied and distributed without alteration for nonprofit educational purposes provided that credit is given to the Mississippi State University Extension Service.


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