Six Ways to Prevent Tomato Diseases

Have you ever worked hard to plant your garden, with dreams of picking red luscious tomatoes – only to see your tomato plants slowly wither away and die before your eyes?

Tomatoes are susceptible to more than three dozen different diseases. However, you will most likely only have to deal with 2 or 3 main diseases in your area. Some diseases are soil-borne, some can be spread by seed, and others through the air or water.

In this article, you’ll learn six basic principles to help keep your tomato plants healthy:

1. Choose Disease-Resistant Varieties
2. Give Your Plants Ideal Growing Conditions
3. Follow Good Sanitation Procedures
4. Reduce the Spread of Disease by Water
5. Sterilize Your Tomato Seeds
6. Use Organic Fungicides (a last resort)

Choose Disease-Resistant Varieties

Disease-resistance has been bred into many newer tomato varieties – some open-pollinated and some hybrids. Many heirlooms are very susceptible to common diseases, though a few offer resistance to a particular disease. For example, the heirlooms “Lemon Drop” and “Mr. Stripey” are resistant to late blight.

Unfortunately, “disease-resistant” doesn’t mean that a particular variety is immune – only less susceptible. You will still need to use the other methods listed in this article to help keep your plants healthy.

Whenever possible, before you choose your tomato varieties and plant your garden, find out what diseases are common in your area – ask your neighbors, local nurseries, farmer’s market, or your local Cooperative Extension office.

If you already have diseased plants, try to identify the exact problem. See the Resource listed at the end of this article for photos and descriptions of various tomato diseases.  Your local Cooperative Extension office may also be able to help you identify your problem.  If you know which disease you’re dealing with, you can then choose a control method best suited for it.

Seed companies use disease codes to let you know which varieties are resistant to which diseases:

F Fusarium wilt
FF Fusarium wilt races 1 and 2
FFF Fusarium wilt races 1, 2, and 3
V Verticillium wilt
N Nematodes
T Tobacco mosaic virus
A Alternaria alternata (stem canker or early blight)
St Stemphylium (gray leaf spot)
TSWV Tomato spotted wilt virus

So, if you see a variety with “VFTN” after its name, it means that it is resistant to 4 diseases – verticillium wilt, fusarium wilt, tobacco mosaic virus, and nematodes.

It’s now also possible to purchase grafted tomato plants, where the rootstock is very resistant to common soil-borne diseases, and the flavorful tomato variety is grafted on top. You don’t need to use grafted plants unless you have a soil-borne disease in your garden. Many companies now offer grafted tomato plants, including: Johnny’s Selected Seeds and Territorial Seed Company.

Give Your Plants Ideal Growing Conditions

Healthy, vigorous plants are less susceptible to disease. You want your plants to be able to grow quickly, with no interruptions.

• Grow your tomato transplants in larger pots, such as 1 quart. Do not let them get pot-bound.
• Provide your plants with deep, well-drained, fertile soil to grow in.
• Grow your tomato plants in full sunlight (preferably 8 hours or more).
• Keep your plants’ soil steadily moist – don’t let the soil dry out, nor stay soaking wet.
• If you have very cool summers, consider growing your tomatoes inside a small hoop house for extra warmth.
• Make sure your garden soil has plenty of organic matter/compost. This will encourage an abundant population of beneficial soil organisms that can help reduce disease problems.
• Wait until the soil is warm and the weather is settled before planting your tomatoes in the garden. Putting them outside when the weather and soil is still cold can stunt their growth for the entire growing season – and make them more susceptible to disease.

Follow Good Sanitation Procedures

• Keep smokers away from your garden, and have them wash their hands thoroughly with soap and water before handling your plants.
• Do not use transplants that are stunted, mottled, or otherwise look ill – you could introduce diseases to your garden.
• Destroy volunteer tomato or potato plants, if you have previously had diseased plants in your garden. They can carry some diseases.
• Grow nightshade family plants (tomatoes, potatoes, eggplants, and peppers) only once every 3-5 years in each garden bed.
• Remove all tomato-related weeds inside or near your garden. These can transmit diseases. This includes nightshades, ground cherries, and horse nettle.
• Remove any diseased-looking leaves as soon as possible – so they won’t spread more spores to the rest of your plant (this won’t work with seed- or soil-borne diseases).
• Disinfect your tools promptly if they have been used near a diseased plant. Also, wash your hands thoroughly after handling diseased plants.
• Avoid putting diseased plants into your compost pile (dispose of or burn the plants instead).

This is especially important for soil-borne diseases. If your plants develop bacterial canker, fusarium wilt, or verticillium wilt – carefully pull the plants up, and dispose of them. Disinfect your hands, tools, stakes or cages. Avoid planting tomatoes, potatoes, peppers, or eggplants in that area for the next 3-5 years.

Reduce the Spread of Disease by Water

Water is an aggravating factor for many tomato diseases. Many fungi thrive in high humidity, especially when the leaves are wet for long periods of time.

Rain can also splash disease spores from the soil up onto the leaves, or spread spores from lower infected leaves to healthy leaves up higher on the plant. That’s one reason why some diseases start on lower leaves and spread upwards.

• Don’t harvest or handle your plants when they are wet – diseases spread more rapidly in water.
• Space your plants far enough apart to provide good ventilation.
• Staking or trellising your plants can provide better ventilation and allow them to dry out more quickly.
• Avoid watering the foliage of your plants, to help keep the leaves dry.
• Another option is to grow your plants inside a hoop house, and water only the soil. In 2013, this allowed me to harvest fresh tomatoes long after all the local gardeners lost their plants to a major outbreak of late blight due to a very wet summer.
• Spread organic mulch over the soil underneath the plants, to help prevent soil-borne diseases from being splashed up onto your tomato leaves during heavy rainfalls.

However, if you have cool summers (highs usually in the 70’s or low 80’s), organic mulch may keep your soil too cool for your warm weather crops to thrive.  You might want to use special red plastic mulch instead, as it can keep your soil warm while helping to reduce the spread of disease. In most other situations, I don’t recommend using plastic mulch.

Sterilize Your Tomato Seeds

Some diseases can be spread by seed. If you experience seed-borne diseases, soak your seeds in a 10% bleach solution (1 part bleach to 9 parts water) for 10 minutes, rinse them well with clear water, and then plant. I haven’t had to use this technique yet, as I haven’t seen any seed-borne tomato diseases in my garden, and I buy high-quality seed from reputable sources.

Use Organic Fungicides (last resort)

Fungicides can’t destroy disease already on your plant leaves, but they can help slow the spread of diseases to uninfected leaves. There are natural fungicides made from copper, sulfur, or baking soda. Some people use compost tea or seaweed solution. It’s best to first remove any infected leaves, and then thoroughly spray your plant with the product.

One of my local organic farmers uses Maxicrop Soluble Powder seaweed solution if his tomato plants start showing signs of disease, despite doing all of the recommended preventive control methods. BioSafe Disease Control 32 oz Ready to Spray is another option. Follow the directions on the labels very carefully.

I haven’t used fungicides yet, as my plants do just fine most years if I give them the best growing conditions possible, and use most of the other control methods mentioned above to help prevent disease. However, these products may have been able to save my outdoor tomatoes in 2013, when late blight killed most plants in my region due to a very wet summer.

Just be aware that preventive fungicides won’t help control seed-borne or soil-borne diseases.

Resource:

Here is one great resource – an article from Clemson Cooperative Extension that includes disease descriptions, some excellent photos, control suggestions for individual diseases, recommended fungicides, and a list of disease-resistant tomato varieties:  Tomato Diseases

Summary

You will have the best chance for growing healthy, vigorous plants that will provide you an abundance of rich, juicy tomatoes by choosing disease-resistant varieties, giving your plants ideal growing conditions, following good sanitation procedures, reducing the spread of disease by water – and, if necessary, sterilizing your tomato seeds or using organic fungicides.