Tomato Troubleshooting Guide

There’s nothing quite like growing your own tomatoes but this can sometimes be a bit of a challenge. They can succumb to so many different pests and diseases, it’s hard to be positive about growing them. With perseverance though, there is light at the end of the tunnel. These are just some of the reasons your tomato plants may not be performing at their best. Catch them early and you could have the best crop of fresh tomatoes ever.

The problems mentioned here are really the beginnings of the things that can go wrong with a tomato plant, but they are perhaps the important things to remember. Other common crop problems can also attack tomatoes so look out for red spider mite, whiteflies, aphids, American bollworm, cutworms, Septoria leaf spot and nematodes as well. At the end of the day, its well worth it for a good crop of tomatoes and there are so many disease-resistant varieties available in seed form that are ready for the season.

1. Not enough sun

Tomatoes are sun-loving plants and need 6 – 8 hours a day. Under 5 hours and the plants will be stunted and unhealthy and will eventually perish.

2. Incorrect watering

Watering is perhaps one of the most important factors in keeping plants healthy and free from fungal and bacterial diseases that will appear when the plants are stressed.

Drip irrigation is the best choice for tomato plants as watering the leaves will promote fungal diseases. Alternatively, water at the base or root zone of the plants to saturate to at least 15 – 20cm below the surface to make sure they have enough to carry through to the rest of the plant. Water 2 – 3 times a week during the summer growing season and reduce this in the cooler months.

Over-watering can cause the roots to suffocate by inhibiting oxygen flow and causing them to rot. A sign of this is fruit that has split skin.

3. Unbalanced soil

Tomatoes prefer loamy soil, but will grow in just about any soil that is not clay. The roots need aeration and the soil should be loose and welldraining. Being heavy feeders, they need plenty of extra compost at planting time and regular feeding. A word of caution though, you can kill off a tomato quickly with too much fertiliser. Too much nitrogen will cause the plants to produce leaves and no fruit and can cause a build up of sediment on the surface of the soil which can then attract fungi. This will need to be scraped off and replaced with an organic mulch. Make sure the feeding programme is adhered to with products that are specifically formulated for tomatoes.

4. Too much heat

A summer heat wave could kill off tomatoes rapidly. Tomatoes like the temperature to be between 20 and 29°C. When it gets higher than that, they may need to be covered with shade cloth. Fruit may develop sunscald – basically sunburn for tomatoes – and this forms blisters that are often attacked by black mould. Remember to keep them watered in extreme heat as well.

5. Nutritional imbalance

As mentioned earlier, tomatoes like to be fed often. When fruiting, they need a flower and fruit formula that contains more phosphorous than nitrogen every 2 weeks. This type of formula also contains other essential nutrients like potassium, calcium, magnesium, boron and zinc. A lack of fertiliser can be seen in yellowing leaves, poor growth, a lack of buds and fruits and sometimes purple-coloured stems.

6. Phosphorous deficiency

In certain circumstances, a tomato plant is unable to absorb enough phosphorous from the soil. The plants will be stunted, the leaves may curl or turn brown or purple. Usually, the soil is too cold or too wet and the pH is off. An acidic soil below a pH of 6.5 and an alkalinity above 7.5 will both have an effect on the plants absorption rate. The solution to this problem is to dig in a high phosphorous fertiliser into the soil or use a seaweed-based liquid fertiliser as a foliage drench to jumpstart the plants enzymes into working.

7. Calcium deficiency

Curling leaves with a dull-looking colour could be a calcium deficiency. This is often the case in soils with a high acidity level and could cause blossom end rot. Bring up the alkalinity of the soil by adding agricultural lime and dig in crushed eggshells. Alternatively use a calcium nitrate fertiliser and water in well at the root zone of the affected plants.

8. Blossom End Rot

When the plant’s ability to absorb calcium is compromised, the plant may develop brown marks at the blossom end of the tomato. This rotting at the ends could be caused by severe drought, pruning and very cold temperatures. Sometimes it is only visible once the fruit is cut and in severe cases it could also cause black mould. Rather prevent the problem by testing the pH 2 – 3 months before planting and adjusting the calcium levels with agricultural lime if necessary or a calcium nitrate fertiliser and water in well at the root zone of the affected plants.

9. Early Blight

Yellowing leaves towards the top of the plant may be a sign of early blight. Early blight is caused by the fungus Alternaria solani and although it can appear at any time of the year, it will usually appear in late spring when the plant starts to fruit and is more prevalent in wet weather.

You can identify early blight by noticing concentric circles with tan centres and yellow halos on fruit and stems that may have sunken dark spots. To prevent this disease, avoid splashing water on plants although spores can be carried by wind. Cut off any infected areas and destroy. Spray with a registered early blight copper fungicide to prevent the spread.

10. Late Blight

Caused by the fungus Phytophthora infestans that also caused the potato famine of 1845, late blight usually occurs in wet weather in summer and autumn. This is one of the most serious fungal diseases that can occur in your garden and there is really nothing that can be done except to act quickly and destroy all signs of the plants. It moves quickly and can kill a tomato plant in a few days. Pale green spots on the tips of leaves are an early indication. Brown spots may appear on green fruit followed by a white mould. Brown and black spots can be present along the entire stem. Regularly use a bio-fungicide for blight as a preventative measure after heavy rain.

11. Anthracnose

This is a fungus called Colletotrichum phomoides and it forms pulpy holes at the blossom end of fruit, more so in overripe tomatoes. It happens more often in humid, hot weather and is often spread by watering the whole plant (not just the root zone) with overhead watering systems. Pick fruits when they are ripe and adjust watering. If severe, there are fungicide treatments available to control this fungus.

12. Canker

Yellow dots with a dark circle around them on ripening fruits is a sign of bacterial canker. This disease called Clavibacter michiganensis is a naturally occurring soil bacteria, although it can also be brought into the garden with other infected plants. Any weak spots on a plant can be a target for infection if water splashes from the soil onto the plant. There is no treatment for this disease and plants will need to be removed and destroyed. No tomatoes can be planted in the same spot for at least 3 years. Avoid canker by watering at the base of the plant and not getting the leaves and fruit wet.

13. Fusarium Wilt

Another fungus caused by Fusarium oxysporum that occurs in the soil. This fungus gets into the roots of the plants and then clogs up the cells as fluid moves through the stems. When water is no longer able to get to the ends of the stems, the plants will die. Look out for yellowing on one side of the plant and brown marks on the stems. Wet weather and bad drainage are often the culprits. There is nothing to do but remove and destroy the plants.

14. Powdery Mildew

This fungus is easy to identify on the leaves of tomatoes by the white powdery substance that covers the leaves. It feeds on the leaves and stems causing them to yellow and the spores move to other plants quickly by wind. Use neem oil or a specific fungicide. Prevent by using a bio-fungicide regularly and making sure there is enough air flow between plants. Remove any infected plants immediately to stop the disease from spreading.

15. Tomato Hornworm

Identifiable by their green colouring with a V-shaped white marking, these pests hide under the leaves by day and only come out at night to feast on the leaves and green tomatoes, destroying an entire plant in a few days. Use an organic pesticide specific to tomato hornworm or hunt them at night with a torch and a bucket of soapy water to drown them in.