Yellow leaves and brown spots on tomato plants are most commonly caused by early tomato blight. Once found, early blight can be managed by regularly removing affected foliage from your garden. However, the best way to manage early blight - or any other tomato disease - is to prevent it from affecting your tomato plants in the first place. Learn how to distinguish early tomato blight from other tomato plant problems, what to do if you find blight in your garden and how to prevent tomato disease from affecting your plants.
What to do if your Tomato Foliage is Turning Yellow
Once you know the basics of tomato plant care it is relatively easy, even for beginner gardeners, to grow a few tomatoes. However, producing any quantity of high-quality tomatoes on plants that thrive throughout the entire growing season is a more challenging task. From pests to disease to environmental stress, you need to learn to identify and respond to the signs of various tomato plant problems as they appear in your garden.
Healthy tomato plants should have full and lush dark green foliage without yellow or brown discoloration or spots. If you find tomato foliage with yellowing leaves, brown spots or other discoloration in your garden, follow these steps:
- Rule out causes of foliage discoloration that are not disease.
- Determine if the disease your tomato plants have is manageable or fatal.
- Properly remove and dispose of infected plants or plant material.
Are your Sure your Tomato Plants have a Disease?
Sometimes yellow tomato leaves are not a symptom of disease at all - especially when there are no brown patches or spots on the plant. These issues are often easy to treat and reverse. Some of the most common causes of yellowing tomato leaves without brown patches or wilting are:
- Your plants need to be fertilized. If your plants have an overall pale green to yellowish green color, it is likely they are not getting the nutrients they need. Feed them with a water-soluble fertilizer like fish emulsion or another liquid feed that is relatively high in nitrogen.
- Iron deficiency. If your plants have an all-over yellowish color but the veins of the leaves remain dark green, they likely have an iron deficiency. Make sure your plants have a nice layer of compost worked into the soil and feed them with a foliar spray that contains iron.
- Your tomato plants are over or under-watered. Tomato plants need 1 inch of water per week (2 during the hottest months of the year). Make sure your plants aren’t getting too much more or too much less water than this.
Looking for more general tomato care instructions? Head over to my post about growing tomatoes for beginners.
Do your Tomato Plants have a Fatal or a Manageable Disease?
If there is no environmental or physiological explanation for the yellowing leaves (like the ones described above), your tomato plants likely have a disease. Plant diseases can be difficult to identify as there are a lot of them and the symptoms can be difficult to distinguish. The good news is you don’t really need to know the exact disease your tomato plants have. All you really need to know is whether your sick-looking tomato plant has a manageable disease or a fatal one.
Fatal Tomato Diseases
The most common fatal diseases you might find on your tomato plants are late blight and fusarium or verticillium wilts. If you find a fatal disease on your tomato plants you need to remove and dispose of the entire affected plant immediately to prevent the disease from spreading to your other plants.
Your tomatoes most likely have a fatal disease if:
- They are dry or dehydrated looking and severely wilting. Some wilting in the hot afternoon sun is normal for healthy tomato plants, but they should perk back up in late afternoon and they shouldn’t be browning.
- Irregularly-shaped brown patches or entire branches turning brown.
- There is fuzzy white growth on the underside of these brown patches.
- From the bottom of the plant up, the foliage is rapidly wilting, rotting and falling off the plant.
- In addition to foliage discoloration and wilt, the fruit is rotting
This guide is meant to give you quick advice on how to handle diseased tomatoes for those uninterested in the details of plant diseases. If you want more detailed information about the various tomato diseases that might affect your plants check out a comprehensive guide to tomato disease from a university or agricultural college extension like this one. This site has a useful gallery of tomato diseases.
Manageable Tomato Diseases
The most common manageable diseases that might affect your tomato plants are early blight and leaf spot. If you find a manageable tomato disease you can leave the plant in place for the growing season. You need to stay on top of maintenance by pruning away affected foliage, sterilizing your pruners before and after you prune foliage off each plant. Tomato plants with manageable diseases should still produce healthy tomatoes.
You most likely have a manageable tomato disease if:
- Yellowing foliage begins on the bottom leaves of the plant and works its way up.
- Yellowing is accompanied by brown bullseye-shaped spots rather than large irregular patches of brown.
- There is no serious wilting of the plant.
How to Dispose of Diseased Tomato Foliage and Fruit
Diseased tomato fruit and foliage needs not just to be pruned from the plant but to be removed completely from your garden and destroyed if possible. Don’t leave affected plant material lying around your garden beds as this can spread the disease.
- Burn it: If you’ve got a fire pit, destroy diseased tomato foliage by burning it.
- Bury it: If you have a large enough property you can also bury diseased tomato foliage. Find a location away from where you plant your vegetables and bury diseased tomato foliage in a hole that is at least one foot deep.
If you are going to compost diseased plant material, make sure you are using a hot and not a cold compost method.
- Compost it: Composting diseased foliage is advisable only if you have a municipal green bin pick-up that will remove the diseased plant material from your property or if use a hot compost method for your DIY compost that gets hot enough to destroy disease spores. Avoid returning composted plant material to your garden that might still contain pathogens or fungal spores.
- Trash it: If none of the above options work for you, dispose of diseased tomato plants and plant material with your regular garbage.
- Stop it from returning next year: Don’t collect seeds from diseased tomato plants and, if space allows, plant your tomatoes in a different location for the next year or two, especially if your tomatoes have a fatal disease.
The Best way to Treat Tomato Blight is to Prevent it.
Some common tomato growing problems are easy to solve as they arise. Hand pick bugs and squish eggs if you encounter pest problems or apply fertilizer or adjust your watering if your plants are pale and stunted. Tomato disease is different. Once infected with disease, your plants can’t be cured, only managed. So the best thing you can do for healthy tomato plants and a productive harvest is to prevent your tomatoes from becoming sick in the first place by making your garden inhospitable to the pathogens and disease spores that cause disease. Practicing good garden hygiene is the single most effective way to ensure healthy, disease-free, tomato plants from seed or transplant to harvest. This means:
- Maintaining good air circulation around your tomato plants.
- Only working in your garden when the plants are dry.
- Always using clean, sterilized garden tools.
- Creating a barrier between the soil and your tomato plants.
- Water your Plants Properly.
- Choose Disease-Resistant Tomato Varieties.
Air Circulation
Tomato diseases thrive in wet, humid conditions. While it’s true that the roots of your tomato plants need to be adequately and consistently watered throughout the growing season, the leaves and fruit of your tomato plants should be kept as dry as possible. Of course, unless your tomatoes are growing in a greenhouse, you can’t stop them from getting wet in the rain. But you can minimize the time your plants spend wet and humid by maintaining good airflow around your plants.
There are a few things you can do to increase the airflow around your tomato plants and limit the opportunity for tomato diseases to spread in your garden:
Leave Adequate Spacing Between your Tomato Transplants
- The proper spacing for tomato plants depends on the type of tomato you are planting and the pruning method you choose.
- If you are growing large determinate varieties or indeterminate varieties and have plenty of growing space, aim to leave 18 inches to two feet between each tomato plant and at least 2 to 3 feet between each row of plants.
The varieties of tomatoes you choose helps determine the spacing, staking and pruning methods you should use.
- If you would like to save space in your garden you can get away with spacing your tomato plants more closely together at around 12-18 inches apart as long as you are either growing dwarf tomato varieties or you are willing to commit to regular and more extensive pruning.
Grow your Tomatoes Vertically
- Technically you can grow tomatoes by allowing them to sprawl along the ground. But, if you want disease-free tomato plants, it’s best to find some way to lift them off the ground so air can circulate around them and the fruit and foliage have less contact with the soil.
- If you are growing dwarf tomatoes or small determinate tomatoes, small tomato cages may be sufficient to contain your tomato plants in an upright position. Otherwise, there are a wide range of techniques commonly used to support larger tomato plants such as tying each plant to a single stake, training them up a string trellis or using the Florida weave or stake and weave method. Try out different methods till you find one you like.
- No matter how you support your tomato plants vertically, they won't climb up the supports on their own. You will need to periodically train them to the supports by tying them up with string, twine, green tying tape or tomato clips.
Prune your Tomatoes for Air Circulation
Remove Bottom Leaves
As your tomato plants grow, remove all of the foliage from the bottom of each plant, aiming to leave 1-2 feet of open space (depending on the height of your plants) at the bottom. You want to be able to crouch down and see through your tomato bed at ground level - with only the stalks of each plant visible.
Prune Suckers
Suckers are branches that begin as tiny shoots between the main stem and the side branches of a tomato plant. If left to grow, suckers become additional “main stems” on your tomato plant that produce branches, fruit and suckers of their own. You can allow all the suckers on your tomato plants to grow but you will have a congested tangled mess of tomato plants that is prone to disease and difficult to harvest from.
Instead, limit the number of suckers you allow to grow on each tomato plant by pruning the ones you don’t want. You may want to prune all of the suckers or, if you have a bit more space, limit each plant to no more than 3 main stems. Suckers continue to appear throughout the growing season, so you need to commit to pruning once every week or two to maintain healthy plants.
Note: determinate tomato varieties don’t need their suckers pruned. Doing so can limit the productivity of the plant.
Stay out of your Garden when it is Wet!
After air circulation, the next best thing you can do to prevent disease on your tomatoes is to avoid working in your vegetable garden when it is wet. If it is raining or your garden is still wet with morning dew, avoid tying up or harvesting your tomatoes and absolutely do not do any pruning until the foliage and fruit have dried.
Always use Sterilized and Sharp Pruners and other Tools
Regular pruning is important to keep your tomatoes at a manageable size with good air circulation around the foliage and fruit. But pruning creates wounds in plants that are susceptible to disease until they have properly healed.
To minimize the damage done to your plants when you prune, it is important to use sharp, sterilized pruners. Sterilize your pruners with ethanol or isopropyl alcohol before you begin pruning and sterilize them again each time you move from one plant to another to avoid transferring disease from a sick plant to a healthy one.
Create a Barrier Between the Soil and the Plants
Many plant diseases are soil-borne. This means that some pathogens and fungal spores live in the soil and can infect any plant material they come in contact with. To prevent this, create some sort of barrier between the soil and your plants.
Defoliation
Not only does pruning the bottom branches of your tomato plants create space for air circulation underneath your plants, it removes any foliage that may droop down far enough to touch the soil and makes it less likely for soil-borne disease spores to splash up from the soil and onto the foliage when it rains or when you are watering.
Mulch
Another strategy for protecting your tomato plants from soil-borne disease is to thickly mulch - aim for a 2-4 inch layer - around the bottom of your tomato plants to create a physical barrier between the surface of the soil and your tomato plants.
Shredded leaves, dried grass clippings, wood chips, hay or straw and compost can all be used as organic mulch materials and each has their pros and cons. Try out different materials until you find one you like, starting with materials that are easily available to you.
Water your Plants Properly
The key to keeping tomato blight and other diseases at bay in your garden is keeping the leaves of your plants as dry as possible throughout the growing season. But whether you grow your tomatoes outside or under cover in a greenhouse, you can’t escape the need for watering. Opt for watering methods that apply the water as close to the soil as possible, so the roots of your plants receive the water they need, but the leaves stay as dry as possible. Watering close to the soil has the added benefit of minimizing splashing, further reducing the opportunities for soil-borne disease to come into contact with your plants
The ideal way of watering your plants close to soil level is to run drip irrigation through your vegetable beds. If you have no choice but to water by hand, avoid watering over the tops of the plants. Instead, place the hose or watering can close to the soil, using a nozzle that doesn’t create too much splashing. This will be easier to do if, as recommended above, you have defoliated the bottoms of your tomato plants.
Ideally, water your tomatoes early in the morning so plants have plenty of time to dry throughout the day and won’t remain wet overnight.
Choose Disease-Resistant Tomato Varieties
Another strategy for preventing tomato diseases from affecting your tomato plants is to choose tomato varieties that have been bred to be less disease-prone when you are seed shopping. This will often mean selecting hybrid, rather than heirloom, tomato varieties.
If you’d like to try growing disease-resistant tomatoes, check out this comprehensive list of disease-resistant tomato varieties compiled by Cornell College of Agriculture.
Remember, disease resistant varieties are less likely to succumb to disease. It does not mean that they are immune to disease. Growing only disease-resistant varieties won’t guarantee that your plants will be completely disease-free throughout the growing season.
.svg)
