Tomato Plant Problems from Diseases to Pests & How to Fix Them

By Emily Murphy

Given the right conditions, tomatoes will practically grow themselves. The basic formula is heat, full sun, nutrient rich soil that’s free draining, consistent water, and room for them to breath. No matter if you’re growing patio tomatoes in containers or vining tomatoes in raised beds, the formula is the same. However, every once in a while problems creep in (quite literally), so it’s best to be prepared and ward them off at the pass.

What do pests and diseases of tomatoes look like and what can you do about them? Your first and best line of defense is to choose tomato varieties that are adapted to your unique climate and resistant to the diseases common to your region.

The next best line of defense is to buy starts that appear perfectly healthy or to grow seedlings to reduce the risk of disease. Nursery starts should be vividly green, perky, and free of any marks, spots, or discoloration.

Once you’ve selected the right healthy tomato varieties, it’s valuable to recognize common pests and diseases and understand simple solutions for remedying problems. To help, we’ll break down the process into 4 components:

1. Pests vs. Disease
2. Common Tomato Pests
3. Common Tomato Diseases
4. Other Common Problems

Pests vs. Disease

First, identify what part of the plant is being affected. Is it the leaves, stem, flower, or fruit that appears disfigured, discolored, or dying? This will help determine if it’s an animal, bacteria, a fungus, or something else entirely.

3 Sure Signs of Pests

1. Leaves or fruits are partially eaten, have holes, or insect tracks are evident
2. Visibly seeing animals, eggs or larvae of aphids, weevils, or caterpillars on or near plants
3. Seedlings disappear completely or plants are defoliated

5 Sure Signs of Diseases

1. Leaves start yellowing or develop brown or black spots
2. Leaf tips turn brown, curl, or shrivel
3. A white film develops on leaf surfaces
4. Fruits have soft spots, rotted stems, or are moldy
5. Seedlings tip over or bend near the base of the stem shortly after the germination process

Common Tomato Pests

• Aphids are tiny winged and wingless insects that are often found on the undersides of leaves or feeding in clusters throughout plant vegetation.

They can be difficult to see, but if ants are present, then aphids generally are too. (Ants like to feed off the sugary honeydew that’s a byproduct of aphid feeding.) Aphids are sap sucking creatures that cause plants to weaken, stunting growth and cause leaves to become misshapen. To rid your tomatoes of aphids, use a heavy stream with a Thumb Control Watering Nozzle to knock them off leaves. Then spray plants with soapy water. If the problems persist, encourage natural predators such as ladybugs.



• Tomato horn worms are large caterpillars with a horn-like tail (see above image).

You’ll find eggs or caterpillars on or near plants in the tomato family. Or you’ll discover the leaves of your tomato have disappeared. Tomatoes are the preferred host plants of these larvae. When you see them, pick them off plants and put them in soapy water. It’s also helpful to keep your garden weed free. These same tips also apply to other caterpillars.

• Slugs and snails love tomatoes as much as you and me.

If you find leaves and fruits with large holes, slugs or snails are near. Look for accompanying slime trails to positively identify. The best remedies for slugs and snails are four-fold. First, water directly above the root crown and not the entire garden. (Slugs and snails prefer moist environments.) Next, inspect plants regularly and handpick any unwanted visitors. If the problem persists, employ traps and/or barriers. Place a shallow dish filled with beer near plants to trap slugs and snails (they’ll climb in and die) or sprinkle a ring of diatomaceous earth around plants to prevent them from reaching crops.

• Whiteflies are bright white, winged insects that form large colonies on the undersides of leaves.

They’re highly visible and, when leaves are moved or disturbed, will fly off in small white clouds of bugs. Like aphids, they’re sap suckers that cause plants to weaken. Spray plants using a heavy stream of water with your watering nozzle and apply insecticidal soap.

• Cutworms are larvae or caterpillars that feed on young plants at night.

If you find seedlings have disappeared by morning, they could be the culprit. To protect plants, place a collar made from cardboard, aluminum, or another recycled material at ground level and around stems to form a barrier.

• Flea beetles are double trouble.

The adults, which are small black beetles that jump like fleas, feed on foliage leaving pits and small holes on leaves. Their larvae feed on roots. These beetles can be controlled by sprinkling plants with diatomaceous earth, introducing beneficial nematodes to soil, and placing row covers over young plants.

Common Tomato Diseases

• Damping-off affects young sprouts and is caused by a fungus found naturally in soil.

If your seedlings suddenly tip over near soil level, wilting at the stem, it’s most likely due to damping-off. To prevent this disease, water seedlings when first planted and then water just enough to keep soil moist but not water logged. Make sure seedlings have room to breathe, giving them plenty of air circulation, and use clean containers and tools when planting and tending plants. If you see plants behaving as if damping-off is occurring, sprinkle cinnamon around the base of plants. It acts as a natural fungicide.

• Bacterial leaf-spot forms small, rough black spots surrounded by yellowing leaves.

It can also occur on fruits. To prevent leaf-spot, grow resistant cultivars, keep your garden weeded, provide plenty of air circulation and sun, and manage water. It’s best to water tomatoes at soil level using a Thumb Control Watering Nozzle and Flexogen Hose. Water in the morning as this will give plants time to dry through the day.

• Fusarium wilt and verticillium wilt are both fungi that access plants through soil moisture.

  While different fungi, they have similar affects. If you see yellowing leaves, leaves that develop large brown splotches, and discolored stems, it’s most likely due to fusarium or verticillium wilt. If your tomato plants are suffering with these symptoms, it’s best to pull them and avoid planting tomatoes again in the same soil. Don’t throw infected plants into your compost, rather put them in the trash to avoid further contamination. Be sure garden tools are clean before your next planting.

  Fusarium and verticillium wilt can be controlled much like leaf-spot. Grow disease resistant varieties, make sure soil has excellent drainage, encourage air circulation, weed when needed, and water at soil level and in mornings whenever possible.

• Early blight causes brown spots with concentric rings and yellow halos to form on leaves, and it eventually causes stems and tomatoes to rot.
• Late blight causes large, dark patches to form on leaves and leaf tips but without yellow halos.

Late blight then spreads to stems and fruits, where more brown spots and even white fuzz can be found. To prevent and control blights, grow resistant varieties, encourage air circulation, keep your garden clean and weeded, and water at soil level and in mornings.

OTHER COMMON PROBLEMS

• Blossom end rot is generally a sign that soil has a calcium deficiency or the pH is off and, therefore, plants can’t access available calcium.

You can test soil for pH, but start by adding an organic source of calcium such as lime, kelp, or ground egg or oyster shells.

• Cracked or split fruit is typically due to extreme fluctuations in watering and temperatures.

It can be difficult and often impossible to control outdoor temperatures and water that comes as rain. However, mulching soil and watering consistently is your best bet for preventing tomatoes from splitting or cracking.