Tomato Pests &
Diseases Guide

A dark, sunken, leathery patch on the bottom of the fruit. Starts small and pale, grows into a large black or brown area as the fruit develops. It hits green fruit just as often as ripe. Only affects the fruit, not the leaves or stems.

Calcium doesn't reach the developing fruit fast enough. This is almost never a soil deficiency. Calcium travels through the plant via water, so when watering swings between too wet and too dry, the plant can't transport it fast enough to keep up with rapid fruit growth. Overfertilizing with nitrogen or potassium also blocks uptake even when calcium is present in the soil.

Large sections of leaves disappear overnight. Entire branches get stripped. The hornworm itself is bright green with white diagonal stripes and a prominent horn at its rear , up to 5 inches long. Dark green droppings on the soil below are the easiest early signal. Use a UV flashlight at night , they glow bright green.

The adult sphinx moth lays eggs on the undersides of tomato leaves in late spring. Each egg hatches into a caterpillar that feeds nonstop for 3–4 weeks. Gardens near woodlines or without row cover protection are most exposed. They arrive in waves , typically one generation in early summer, sometimes another in late summer.

Clusters of tiny, pear-shaped insects on new growth and leaf undersides. Can be green, yellow, black, or white. Leaves may curl or look distorted. A sticky residue on leaves (honeydew) is a reliable sign , sometimes followed by sooty black mold growing on it.

Aphids reproduce asexually , a single aphid can produce dozens of offspring in a week. They're drawn to lush, nitrogen-rich new growth. Overfertilized plants are bigger targets. They also spread plant viruses as they feed, which makes early control more important than the colony size suggests.

Deep, irregular holes bored into ripening fruit , often at the stem end. The inside is hollowed and filled with dark frass. The caterpillar is yellowish-brown with dark stripes and is usually found inside the fruit. Small, dark entry holes are the first sign , probe inside and you'll find tunneling in the flesh.

The tomato fruit worm moth lays eggs on leaves and developing fruit in early summer. Larvae hatch and immediately burrow in, where they're protected from sprays. One larvae per fruit is typical , they're territorial. Warm, dry summers and adjacent corn crops increase pressure significantly.

Small, dark, water-soaked spots on leaves surrounded by a yellow border. Centers dry out and fall away, leaving jagged holes. On fruit: small, raised, dark brown spots with a waxy white border , concentrated on the shoulders of green fruit. Stems and calyx may also show brown spotting.

Caused by a bacterium that thrives in warm (75–86°F), wet conditions. It spreads rapidly via rain splash, overhead irrigation, and handling wet plants. It can survive on infected seed and plant debris in the soil , which is why it tends to reappear in the same bed year after year.

Gray-green spots on leaves that develop a fuzzy gray bloom , that's the mold sporulating. Leaves dry up and die. On stems, look for a brown, water-soaked lesion, especially near the soil or at a pruning cut. The fuzzy gray coating is the giveaway , nothing else looks quite like it.

Botrytis cinerea lives on dead plant matter and becomes a parasite when humidity stays high (above 90%) and temperatures are cool (60–75°F). It enters through wounds, dead flower petals, or damaged tissue. Dense plantings with no pruning create the exact microclimate it needs.

White or light gray powdery coating on the upper surface of leaves , starts as circular spots and spreads to cover entire leaves. Yellow spots may appear alongside. Heavily infected leaves brown and drop. Unlike most fungal diseases, it thrives in warm, dry conditions , it doesn't need wet leaves to spread.

Fungal spores spread through the air , wind, insects, and clothing all carry them. Warm days followed by cool nights create ideal conditions. Dense plantings and over-fertilizing with nitrogen both increase susceptibility. Older, lower leaves are typically hit first.

Bacterial wilt is caused by Ralstonia solanacearum, a soilborne bacterium that invades the plant's water-conducting vessels and produces a slime that blocks water uptake. Plants wilt rapidly — often a single branch first, then the whole plant within days. Unlike other wilting diseases, bacterial wilt moves fast and is always fatal. There is no cure once a plant is infected.

The classic test: cut a wilted stem near the base and hold the two ends close together in a glass of water. If thin, white, thread-like bacterial strands stretch between the cut ends, it's bacterial wilt. Leaves wilt suddenly during the heat of the day but may appear to recover overnight in early stages. The collapse accelerates quickly.

The bacteria is primarily spread by cucumber beetles feeding on infected plants and then moving to healthy ones. It also spreads through contaminated soil, water, and tools.

Early blight is caused by the fungus Alternaria solani. It starts on the oldest, lowest leaves and works its way up the plant. The telltale sign is dark brown spots with concentric rings — like a bullseye or target — surrounded by a yellow halo. It weakens the plant over time but rarely kills it outright. Most common in warm, humid conditions.

Look for dark brown circular spots with clearly defined rings on lower leaves first. The surrounding leaf tissue turns yellow. As it progresses, affected leaves drop off, exposing fruit to sunscald. Stems can develop dark, sunken lesions at the soil line — a condition called collar rot.

Late blight is caused by Phytophthora infestans — an oomycete (water mold) that thrives in cool, wet conditions. Unlike early blight, late blight spreads with terrifying speed and can kill an entire plant in 3 to 5 days under the right conditions. It spreads through the air as spores and can travel miles from infected plants.

Look for irregularly shaped, water-soaked dark lesions on leaves and stems — often with a white, fuzzy mold on the underside of leaves in humid conditions. Lesions are not circular like early blight; they look more like bruised, greasy patches. Fruit develops firm, dark, greasy-looking brown rot. The smell is distinctive — slightly rotten.

Septoria leaf spot is caused by Septoria lycopersici, a fungus that appears shortly after the first fruits set. It starts on the lowest leaves and moves upward rapidly. Left unmanaged it can defoliate an entire plant by midsummer, leaving fruit exposed and yields dramatically reduced.

Spots are small, circular, and numerous — typically an eighth of an inch in diameter. They have a dark brown border with a tan or gray center. Look closely and you can see tiny black specks in the center of each spot — these are the fungal fruiting bodies. This is the key difference from early blight, which has larger spots with concentric rings.

Tobacco Mosaic Virus (TMV) is one of the most resilient plant viruses known. It can survive on dried plant material, tools, clothing, and even in cigarette tobacco for years. It spreads through mechanical contact — touching an infected plant then touching a healthy one. There is no treatment. Infected plants must be removed.

The classic sign is a mosaic-like mottling of the leaves — patches of light green, yellow, and dark green in an irregular pattern. Leaves may also look blistered, curled, or distorted. Young leaves are often narrower than normal and may have a fernlike, stringy appearance called "shoestring." Fruit may show yellow rings or internal browning.

If you smoke: wash your hands thoroughly with soap before touching tomato plants. Cigarette tobacco frequently carries TMV.

Spider mites are not insects — they are arachnids, closely related to spiders. They are barely visible to the naked eye and live on the undersides of leaves, piercing plant cells and sucking out the contents. A single female can lay hundreds of eggs and a colony can explode in days during hot, dry weather. They thrive when plants are stressed.

Look for stippling — tiny yellow or white dots scattered across the upper leaf surface where mites have fed. Leaves may look dusty, bronzed, or washed out. Check the underside of leaves for fine webbing and tiny moving dots. The webbing is the giveaway. Shake a leaf over white paper — if tiny specks move, you have mites.

Whiteflies are tiny, white-winged insects that cluster on the undersides of leaves and feed by sucking plant sap. They excrete a sticky substance called honeydew that coats leaves and encourages black sooty mold to grow. Heavy infestations weaken plants, cause leaf yellowing and drop, and can transmit viruses between plants.

Gently shake or brush against the plant — whiteflies take flight in a visible white cloud when disturbed. Check the undersides of leaves for clusters of tiny white insects and their pale, scale-like eggs and nymphs. Leaves may appear yellowed, sticky, or coated with black sooty mold from their honeydew deposits.

Cutworms are the larvae of various moth species. They live in the soil and emerge at night to feed, cutting through seedling stems at or just below the soil line. A cutworm can sever an entire transplant in a single night. They are most destructive right after transplanting when stems are young and tender.

You won't see them — they hide in the soil during the day. What you'll see is a severed seedling, cut cleanly at the base, lying on the ground. Dig an inch or two into the soil around the base of cut plants and you'll often find a fat, gray or brown caterpillar curled in a C-shape. That's your culprit.

The brown marmorated stink bug (BMSB) is an invasive species from Asia now found in nearly every US state. Shield-shaped, mottled brown, and about the size of a dime. They feed by piercing fruit with needle-like mouthparts and injecting digestive enzymes — essentially liquefying the flesh inside before sucking it out. The damage isn't obvious from the outside, which is what makes them so frustrating.

On the outside: look for tiny yellow or white pinprick marks on the fruit surface, often near the stem end. Surrounding tissue may turn yellow or stay pale green on ripe fruit. Cut the tomato open and you'll find dry, spongy, pale, or corky areas just under the skin — that's the real damage. Heavily infested fruit may show cloudiness throughout. Shake a plant over white paper and watch for the bugs to drop. They're there — they're just good at hiding.

Fusarium wilt is caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici. It enters through the roots, invades the plant's water-conducting vessels, and blocks water uptake from the inside. Once infected, a plant cannot be saved. The fungus can survive in the soil for up to 10 years without a host — which is why crop rotation matters so much.

The classic sign is one-sided wilting — only half the plant, one branch, or even one side of a leaf turns yellow and wilts while the other side looks fine. This asymmetry is the key diagnostic clue. Lower leaves yellow first. The plant may appear to recover overnight early in the infection but eventually collapses entirely. Cut the stem near the base lengthwise — you'll see brown streaking in the vascular tissue just under the outer layer. The pith (center) stays white.