GARDENING: Accurate diagnosis critical to resolving disease, pest issues with tomato plants

Credit: Contributed

Credit: Contributed

By now, if you are growing tomatoes, it’s likely that you are seeing some of the leaf spot diseases. We have had the perfect environmental conditions for them to develop this season. I have bacterial spot on all of my San Marzano and a few of the heirloom varieties.

A couple of weeks ago, James Clemmons sent me the following in an email:

“I was hoping you would be able to recommend a comprehensive resource for vegetable plant disease and insect damage issues. In print or electronic. I’ve been having issues and without correct diagnosis I haven’t resolved my issues. It would also be a great resource for the future.”

First, thanks for the idea for his column James, and second, sorry I didn’t do it last week due to the sunflower head-clipping weevil popping up in gardens.

I also want to commend on the comment, “without correct diagnosis I haven’t resolved my issues.”

Knowing the pest problem you are trying to manage is critical to resolving plant problems. Therefore, accurate diagnosis is essential.

The first step is to identify the plant with the second step being researching common problems for the plant in question.

Let’s take tomatoes. If you look up any university factsheet or a research-based resource, you will find the following disease problems listed for tomatoes: early blight, late blight, bacterial spot, Septoria leaf spot, and so on.

Once you find the common diseases, you can then begin your research on those diseases and try to narrow it down to the symptoms that you are seeing on your tomatoes.

If you aren’t successful in your research, check out your local Extension office to see if they have anyone who can assist you. Many offices in the Miami Valley have either Master Gardener Volunteers or an Extension Educator who might be able to help identify the problem.

You can also check with your local garden center to see if someone there can correctly identify a plant problem.

Once you determine the problem, look at all the solutions. We try to utilize integrated pest management (IPM) strategies to reduce the amount of chemicals used.

You may even find that it’s too late to do anything or that there is no action needed. For instance, with bacterial spot, you need to have a fungicide on the leaf surface prior to infection. After the symptoms show up is too late.

A good resource to help is Cornell’s Vegetable Program website. Just enter that title in a search engine and it will come up.

Another good resource is the UC Davis IPM website. I use this site frequently when looking for IPM recommendations. While the site is based on California crops, the crops are many of the things we plant. You just must keep this in mind when searching for information.

Finally, the University of Georgia has a smartphone app called Vegetable Doctor which has all the vegetables and all of the pest problems along with photos listed.

I hope this is helpful to all.

Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at

Credit: Contributed

Credit: Contributed

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