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

Gardening

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.

So, 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 minutes it takes to ask questions at your local garden center and cross check varieties before planting, can save hours of frustration and possibly an entire crop. There are a few varieties, like ‘Celebrity,’ ‘Early Girl,’ and ‘Better Boy,’ with excellent disease resistance that also grow well across regions, but there are many other wonderful varieties to choose from.

Your next best line of defense is to buy starts that appear perfectly healthy or to grow your own 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:

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 that’s decided to take up residence in your tomato patch, bacteria, a fungus, or something else entirely.

3 Sure Signs of Pests

1. Leaves or fruits are partially eaten, have holes in them, or tracks or paths are evident where insects have burrowed their way through plant parts.
2. You can visibly see animals or the eggs or larvae of animals like aphids, weevils, or caterpillars on or near plants.
3. Seedlings disappear completely or plants are defoliated.

5 Sure Signs of Diseases

1. Leaves develop brown or black spots and yellowing may occur in these same areas.
2. Leaf tips turn brown, curl, or simply shrivel.
3. A white film develops on leaf surfaces.
4. Fruits have strange 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 sometimes 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 causing leaves to become misshapen. To rid your tomatoes of aphids, use your Thumb Control Watering Nozzle to knock them off leaves with a heavy stream. 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, most likely feasting away, or you’ll simply 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 that may come looking for a free lunch.

Slugs and snails love tomatoes as much as me and you. You’ll know they’ve been visiting if you find leaves and fruits with large holes. Look for accompanying slime trails to positively identify. I find the best remedies for slugs and snails are 4 fold. First, focus where you water with your nozzle to target watering 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’re 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, they will fly off in small white clouds of bugs. Like aphids, they’re sap suckers, weakening plants in the process, and they can be controlled in much the same way. 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. They can be controlled by sprinkling plants with diatomaceous earth, introducing beneficial nematodes to soil, and by 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 damping-off, 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 on or near leaf tips, and discolored stems, it’s most likely due to fusarium or verticillium wilt. If you find 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 (put them in the trash to avoid further contamination) and 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 or 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 or in mornings.

OTHER COMMON PROBLEMS

Blossom end rot is generally a sign that soil has a calcium deficiency or the soil pH is off and plants can’t access available calcium. You can test soil for pH, but I always 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.

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