Tomatoes are very generous plants but they also get sick with an awfully long list of diseases!
In fact, from blight to spotted wilt virus there are 63 different ailments that your tomato plants can catch!
If you want to avoid becoming a nurse to your tomato vines, you have a way out though: disease resistant varieties of tomatoes!
Disease resistant tomatoes are varieties selected and bred over the years to resist some of the most common tomato ailments like Fusarium and nematodes. Each variety is resistant to some, even most, of the common diseases, but not all. For this reason, we have divided the varieties into categories according to the diseases they are resistant to:
This article will guide you through the problems of tomatoes and disease, and best tomato varieties that have some level of resistance to late blight and other diseases for your area that will grow best where you live.
Why Tomatoes Catch Diseases?
Some plants are naturally disease resistant, others, like tomatoes, are not. But the question is why? Think about the tomato vine: where does it come from? What does it look like? How does it grow? The answers to these questions will explain why they are so “disease prone”.
But… if you risk getting your tomatoes more susceptible to diseases if you select the, for example, for their fruit size, you can also select them for their resistance to diseases…
How Are Disease Resistant Tomatoes Developed?
Disease resistant tomatoes are bred to be such. But what does it mean, in detail? There are basically two ways to go about it: selection and hybridization.
We say selection when we choose to reproduce (seed and grow) tomatoes with a specific quality. Let me give you a practical example.
Imagine you have a filed of San Marzano tomatoes and they catch blight. Most of them get sick, many die…
But you notice that some plants don’t get it!…
What does it mean? It may mean that they have the ability to fight it off in their genes.
So you seed these, and grow them. They catch blight too, but less than before.
You grow the ones that don’t… and so on for a few generations, till you see that your tomatoes just don’t catch blight. You have “isolated” the ones hat are resistant to this disease.
Hybridization is when we mix two varieties of tomatoes. Some varieties can be resistant to some diseases naturally.
If you cross them with a non resistant variety, some of the offspring will have the right genes to be resistant.
You select these, and not the ones that catch it, and you get a new variety which is resistant like one of the parent varieties.
All very scientific, isn’t it? But how about GMOs?
Disease Resistant Varieties and GMOs
GMO technology is not just breeding or hybridization. It means changing the DNA of plants directly, with bits of DNA imported from outside.
There are some GMO tomatoes that are disease resistant, but we will not be presenting them here.
GMOs are a massive ethical and environmental issue and an economic one as well.
We will only give you hybrids and cultivars produced naturally, through the toil and experience of farmers, growers, gardeners and botanists.
But what types of disease can your tomato vines catch?
Types of Tomato Diseases
We said that there are in all 63 known diseases that can affect your tomatoes. They can affect roots, stem, leaves, flowers or fruits.
Basically there are ailments for each part of your tomato plants. But some are common, others are not. Some are very serious, others are less serious.
Anyway, these disease can be grouped into big categories:
These are pathogen caused diseases.
There are other smaller categories (like viroids and omyocetes) like these, but we are not writing a scientific study on tomato diseases, are we?
But then there is another group of diseases which has “no resistance” because these are cause by us or other factors, not pathogens:
Ok, you got the point. Disease resistant tomato varieties are resistant to ailments caused by pathogens, not others.
There is no variety that can resist impoverished soil, which is by far the biggest cause if plant disease all over the world.
How to Understand Disease Resistance Codes for Tomatoes
Here cones the easy bit! Tomato diseases have codes! Scientists, growers, and gardeners have made it easy to understand which disease a tomato variety is resistant by inventing some easy codes (a few letters) that you can find at the back of your seed packet.
So, whenever you buy tomato seeds, do check out these codes, and they will tell you if and which diseases the tomato variety you are about to buy is resistant to:
How To Read Tomato Disease Resistance Codes And Chart
Just look on the seed packet; if you see one of these codes, it means the variety your are buying is resistant to it. But there is another code you can find, and it tells you “how strong” the variety is against the disease in question:
Tomato Diseases in Your Local Area
But which diseases should you look out for to protect your tomato plants and crops? True, you need to know which tomato diseases are typical of your area. There are two ways to go about it.
If you know of any diseases that have or are affecting your local area, make sure you get resistant varieties. You can also check online; there are basically maps of diseases.
For example, anthracnose (code A) is common in the Southern, mid Atlantic and mid Western parts of the USA, while alternaria stem canker (AL) is common all over the USA.
But there is also the climate of your area that tells you which are the more probable diseases. In fact, tomatoes do not get the same diseases and types of diseases in hot and dry regions or in wet areas, for example.
Bacteria Wilt (BW), for example is typical of hot and humid places, while Fusarium crown and root rot attacks plants in cool soil and in greenhouses.
Nematodes (N) too like warm and and humid conditions, while corky root rot affects tomatoes in colder regions, like Canada or the Northern USA.
We almost there now, we are almost about to meet some disease resistant tomatoes, just after a final tip, though.
Non-Pathogen Caused Tomato Diseases and Problems
We are now giving a quick look at the other diseases, those that don’t come from pathogens, like bacteria and viruses, and how to avoid them.
In tact, there is no point in choosing disease resistant tomatoes if you then leave them exposed to other health problems.
Let’s start with a healthy environment. The ideal place for a tomato vine has healthy and fertile water, abundant water, hot and well ventilated air.
This last factor is important. The ideal air humidity for tomatoes is between 50 and 70% on average, and it can even higher indoors, but… you need to ventilate it for about 8 hours a day in a greenhouse. Stuffy air is a real problem with tomatoes.
Gardeners know also that tomatoes eat a lot!
They like nutritious soil rich in organic matter. The problem with most soil nowadays is that it is depleted; it needs constant feeding and fertilizing because it cannot retain the nutrients that tomatoes need.
If your soil has been cultivated organically, and especially with permaculture, this would be very good for tomatoes.
Tomatoes also need regular watering; if you notice that the top leaves become limp, it means the tomato vine is thirsty.
Finally, make sure you give your tomato plants appropriate spacing. Plants that are too near to start with block ventilation; secondly, they can compete with each other, and thus weaken each other. Finally, they can spread infections from plant to plant.
Once you have taken into account all these factors, you can finally choose some disease resistant tomatoes to grow in your garden (greenhouse, in pots etc…).
And we are going to help you with your choice right now!
Our Categories (Groups) of Disease Resistant Tomatoes Explained
Let me explain to you how we came up with these groups. They are not “scientific” groups, but we have put them together according to which disease or group of diseases they are resistant to. This makes the lists we are going to show you very practical.
Fusarium and Verticillum Resistant Tomato Varieties
Fusarium and Vericillum are very common diseases with tomatoes. They are both fungi and they affect most regions of the USA. For this reason, choosing a variety that is resistant to these two pathogens is very wise indeed!
Fusarium, Verticillum and Nematode Resistant Tomato Varieties
If you live in an area where the soil is moist, your tomatoes also risk nematodes. These are parasites that affect the leaves and the roots of tomatoes. They are common in many areas of the USA and Canada too.
So here are varieties that are resistant to these 3 types of disease.
Fusarium, Verticillum, Nematode and Tobacco Mosaic Virus Resistant Tomato Varieties
On top of the three pathogens we have seen so far, there is tobacco mosaic virus which is very common. You can find it all over the world, and it is, as it says on the tin, a virus. But it also has a strange behavior. It spreads by using garden tools after you have used tobacco products. Basically, if you smoke the do a spot of gardening, you may be spreading the virus.
It won’t kill your tomatoes but it will damage the florets and the leaves and reduce the yield of your crop. So, here are varieties that can resist even this strange virus on top of the other common diseases.
Most Blight Resistant Tomato Varieties
Blight is one of the most common diseases of all plants, not just tomatoes. It too is a fungus and it is typical of warm regions of the USA.
You will recognize it because it forms dark spots on the lower leaves. Then the spits get larger and larger and the leaves drop off.
It will weaken the plants and reduce your crops. In some cases, it can also ruin your tomato fruits though. In fact, in hot regions, the tomatoes may literally crack.
So, here are some blight resistant tomato varieties to grow in your garden.
Now you know a lot about tomato diseases. You know how they get them. You know which ones are more common.
You know how to read the signs on seed packets that tell you which diseases the tomatoes are resistant to.
You also have a very long list of tomatoes resistant to common diseases and how to avoid problems that don’t come from pathogens.
And I hope this will soon translate into healthy tomatoes in your garden and bigger, but also tastier crops for you, your family and your friends!
Amber Noyes was born and raised in a suburban California town, San Mateo. She holds a master’s degree in horticulture from the University of California as well as a BS in Biology from the University of San Francisco. With experience working on an organic farm, water conservation research, farmers’ markets, and plant nursery, she understands what makes plants thrive and how we can better understand the connection between microclimate and plant health. When she’s not on the land, Amber loves informing people of new ideas/things related to gardening, especially organic gardening, houseplants, and growing plants in a small space.