How to Recognize (and Prevent) Problems With Your Tomato Plant

Tomato plants are a popular addition to vegetable gardens, but they can be a real challenge. From the moment tomato seeds sprout to the day you compost the plant at the end of the season, tomato plants are surprisingly susceptible to problems. Now that most of you should have your tomato plants in the ground, here’s how to identify problems on your plants, as well as prevent and treat them. 

Stimulate more flower production 

In order to produce tomatoes, you need flowers on your tomato plants, since the pollination of those flowers is what creates tomatoes. While they’ll usually do this on their own, if you notice there aren’t a lot of flowers or you just want to encourage more, you can try using products designed to stimulate flower growth. Sea Magic Organic Growth Activator, made from seaweed, should be used in addition to your regular fertilizer program because it will stimulate flower growth in tomato plants. Sea Magic is easy to use and safe for the home garden. This Tomato & Vegetable Blossom Spray Set contains the plant hormone cytokinin and promotes cell division in plants, which leads to blossom set (flowers developing on the plants), fruit development, and increased yields. This means more potential for fruit set (fruit developing on the plants), even in less desirable weather, as the more flowers, the more fruit.  

Prevent and treat blossom end rot (BER)

The most common tomato growing problem in the world is blossom end rot, which manifests as the bottom of your tomatoes being black, sunken or shriveled.

BER is hard to treat—the problem happens long before you see it in the fruit and is usually a result of a plant’s lack of ability to absorb calcium. This can be because there isn’t enough calcium in the soil, or the plant suffers from another nutrient deficiency (too much nitrogen, not enough phosphorus/potassium) that causes it to not be able to access the calcium in the soil. It can also be due to drought stress, or inconsistent watering. Inconsistent can mean over- or under-watering, which is why it’s important to consistently deliver water directly at the root of your tomatoes. Soil conditions, like compacted or poorly draining soil, can also hinder calcium uptake. 

According to Nancy Awot-Traut, Horticulture Expert at Burpee Gardening, a key challenge for gardeners is that the symptoms of BER, such as fruit rot, typically appear days to weeks after the initial water stress or nutrient imbalance occurs. The most critical time to avoid BER is the first two to three weeks after fruit set. Avoiding BER means getting your soil tested to make your pH is 6.2-6.8, and has enough calcium. According to Awot-Traut, it’s important to avoid over fertilization, since that can result in too much nitrogen. Mulching at the base of plants can help maintain consistent moisture, and ensuring that each tomato plant has enough space (this will depend on the variety and should appear on the seed packet or plant label, but at least 18 inches is standard). 

Once you see BER, it’s too late for affected tomatoes, but you can try to treat the plant for future tomatoes by using a foliar spray like Rot Stop or Cal Mag. 

Prevent virus and fungi

With all the moisture involved in growing tomatoes as well as density of the leaves, there’s a lot of opportunity for the spread of virus and funguses. One of the primary ways fungi spread is by splashing up from the soil when there’s a lot of rain or overhead watering. Mulching and watering at the base of plants prevents this problem from happening. Ensuring that each plant has enough space around it and is pruned to create air flow can help mitigate the spread. Choosing to grow varieties that have good disease resistance can help as well. 

Remember, in the garden you are the most likely vector of disease spread. When you go out into the garden and touch all your plants in the morning, with the dew still present, you may just be spreading whatever is on one plant to all the others. This is also the reason it is critical you keep your pruning shears clean between plants. A spray bottle of Lysol that you use between plants is effective. 

Unlike other fruit that have only a few recognizable issues, tomatoes can suffer from a litany of different fungi or viruses. Septoria leaf spot is a fungus that appears as black spots on your leaves and spreads quickly. Leaves progressively turn yellow and die.

Blight, another common fungus, manifests as irregular black shapes on your tomato leaves.

Fusarium wilt fungus will yellow the leaves, which then turn brown, from the outside of the leaf towards the stem.

Anthracnose is a whole class of fungus that will cause large black or brown spots on your tomatoes. 

Bacterial speck and bacterial spot show up as small brown spots, and are a result of bacteria in the soil that can overwinter.

Mosaic virus is likely the cause of shrunken, twisted and curled leaves.

The most effective treatment for virus or fungus is being bold about removal. Rather than treat plants, the best course is usually swiftly removing the affected plants and then ensuring they go in the trash, rather than compost. If you wait, you risk the problem spreading to all the other plants around the affected one, and in a short summer season, it’s rarely worth that risk. While some fungicides may help treat the problem, you are then introducing those chemicals into your food. It’s safer to take the loss and hope your other plants do better. Remember that the fungus and viruses can remain in the soil over winter which is why crop rotation (moving your crops around in the garden every year) is essential.

Recognize tomato pests

As if the viral and fungal threats aren’t enough, you also have a lot of pests in the garden that will aim for your tomatoes. The best way to mitigate this is to ensure that you are checking your plants daily, diversifying your varieties and planting deterrents around the tomatoes like marigolds, sweet alyssum, dill, and nasturtiums, which will help drive these pests away. The upside is that many of these pest problems can be treated. 

Tiny white or yellow spots can mean spider mites, which will steal chlorophyll from your plants.

Aphids, a common pest problem that you can actually solve, look like tiny white raised dots on your plants that cluster and cause tomato leaves to curl. Spray them off with water, plant nearby trap plants like nasturtiums and treat the tomato with a spray of soapy water.

Tiny round holes in tomato leaves are likely due to flea beetles, and can be managed the same way, with soapy water and nearby traps like yellow sticky traps.

Hornworms are gigantic green worms on your tomato stems that look like tomato stems but will devour your plants. They can simply be removed by hand. 

Everyone thinks of tomatoes as the first thing to grow, and there are few treats as lovely as a sun-warmed, just-ripe tomato you grew yourself. But the road to getting a healthy tomato is long and full of threats to derail your fruit production. Knowing what those threats are, and working to prevent them—and, if possible, mitigate them—will make it a more satisfying season.