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30 pests & diseases
Aphids
Soft-bodied sap-sucking insects 1–3 mm long that cluster on new growth and leaf undersides in large colonies. They can be green, black, white, or grey depending on species. In warm weather aphid populations double every few days, making early action essential.
Tomato Hornworm
The larval stage of the Five-Spotted Hawk Moth, this caterpillar grows up to 10 cm long and is bright green with white diagonal stripes and a distinctive rear horn. Its camouflage is excellent and it can strip a tomato plant rapidly before being noticed.
Cabbage Worm
The pale green caterpillar of the Small White butterfly (Pieris rapae), typically 2–3 cm long and covered in fine hairs. Adults are the familiar white butterflies seen fluttering around brassicas in summer. Both larvae and eggs are superbly camouflaged against the plants they infest.
Japanese Beetle
A metallic blue-green beetle with copper wing covers, about 12 mm long. Adults skeletonise leaves and damage flowers and fruit in midsummer, while their c-shaped white grubs live underground and feed on roots. They aggregate on favoured plants, and a single plant can attract dozens.
Squash Bug
A flat, grey-brown bug about 15 mm long that overwinters as an adult in garden debris and emerges in late spring to attack cucurbit crops. By piercing plant tissue and injecting toxic saliva, it can cause rapid vine death — a problem compounded by its ability to carry cucurbit yellow vine disease.
Cucumber Beetle
Small yellow-green beetles (6 mm) with either black spots or black stripes. Both species cause feeding damage but are most damaging as vectors of bacterial wilt and cucumber mosaic virus, which they transmit when feeding. A plant can look healthy one week and be wilting irreversibly the next after beetle feeding.
Flea Beetle
Tiny jumping beetles (1–3 mm) that create characteristic shotgun-blast patterns of small holes in leaves. Multiple species attack different crops; the crucifer flea beetle is most common in vegetable gardens. Seedlings are most vulnerable — adult beetles overwinter in leaf litter and emerge hungry in early spring.
Whitefly
Tiny (1–2 mm) white-winged sap-sucking insects that cluster in large numbers on leaf undersides. They excrete sticky honeydew, promote sooty mould, and can spread plant viruses. Populations build extremely rapidly in warm, sheltered conditions and are a particular challenge in greenhouses and polytunnels.
Spider Mites
Microscopic eight-legged arachnids (not technically insects) that pierce plant cells to feed on sap. Nearly invisible to the naked eye, they are most problematic in hot, dry weather and can build to devastating population densities within days. The fine webbing they produce is often the first sign of a significant infestation.
Slugs and Snails
Soft-bodied molluscs that rasp holes in plant tissue using a toothed radula tongue. They are nocturnal and most active in wet weather and mild temperatures. Seedlings and low-growing soft-leaved crops are most vulnerable, and a single night's activity can destroy an entire bed of newly transplanted lettuces.
Colorado Potato Beetle
A distinctive beetle with cream wings boldly striped in black, about 10 mm long. Both adults and the bright orange-red larvae cause severe defoliation of nightshade family plants. It can develop resistance to insecticides rapidly, making organic management approaches more durable than chemical options.
Earwigs
Brown nocturnal insects (12–15 mm) with characteristic rear pincers. They are omnivores — they eat both plant material and pest insects including aphids, mites, and small caterpillars. In most gardens they are more beneficial than harmful; significant damage occurs only when populations are very high or plants are already stressed.
Powdery Mildew
One of the most common fungal diseases in the garden, caused by several related species. Unlike most fungi, powdery mildew actually thrives in warm, dry weather with poor air circulation, rather than in wet conditions. It affects an enormous range of crops and is almost universal in humid temperate climates.
Early Blight
A fungal disease caused by Alternaria solani that affects tomatoes and related crops. It begins on the oldest lower leaves and progressively moves up the plant over the season. It rarely kills established plants outright but reduces vigour, causes premature defoliation, and can significantly reduce yield.
Late Blight
The most destructive disease of tomatoes and potatoes worldwide, caused by the water mould Phytophthora infestans — the same organism responsible for the Irish Potato Famine. In cool, wet weather it can kill an entire plant within days. Once it is established in a planting, complete loss is possible.
Damping Off
A collective term for seedling collapse caused by soil fungi and water moulds (Pythium, Fusarium, Rhizoctonia) that attack seeds and seedlings at or below the soil surface. It is the most common cause of seedling death in indoor propagation and is caused almost entirely by overwatering and poor airflow — both of which are fully preventable.
Downy Mildew
A water mould (oomycete) disease that, despite its name, is not closely related to powdery mildew. It thrives in the opposite conditions — cool, wet, and humid weather — and different strains are specific to different plant families. It can be confused with powdery mildew but the spore growth is on the underside of leaves, not the top.
Bacterial Wilt
A bacterial disease caused by Erwinia tracheiphila, transmitted exclusively by cucumber beetles as they feed. The bacteria colonise the plant's water-conducting xylem vessels, blocking water movement and causing rapid collapse. There is no treatment once a plant is infected — prevention and cucumber beetle management are the only defences.
Fusarium Wilt
A soil-borne fungal disease caused by Fusarium oxysporum with many crop-specific strains. The fungus enters through the roots and colonises the vascular system, blocking water transport. It can persist viable in soil for 20 years or more, making rotation planning critical for affected beds.
Root Rot
A collective term for root disease caused by water moulds and fungi (primarily Pythium and Phytophthora) that attack roots in waterlogged or poorly-drained soils. It is almost entirely a condition-driven problem — the pathogens are ubiquitous in soil, but only cause disease when plants are kept too wet. Improving drainage resolves most cases.
Mosaic Virus
A family of plant viruses transmitted primarily by aphids that cannot be cured once a plant is infected. Multiple species infect different hosts — Cucumber Mosaic Virus, Tomato Mosaic Virus, and Tobacco Mosaic Virus are among the most common. Management focuses entirely on prevention and immediate removal of infected plants.
Septoria Leaf Spot
A fungal disease caused by Septoria lycopersici that is one of the most common foliar diseases of tomatoes worldwide. While it rarely kills plants outright, it causes progressive defoliation that reduces photosynthesis, weakens plants, and reduces yield. The spores live in infected debris in the soil and are splash-distributed to lower leaves.
Botrytis (Gray Mold)
Botrytis cinerea is one of the most widespread fungal diseases affecting both garden plants and stored produce. It infects primarily through damaged, dying, or senescent tissue and spreads rapidly in cool, humid, still-air conditions. Soft fruits — strawberries, raspberries, grapes — are particularly vulnerable at harvest.
Rust
A large group of highly host-specific fungal diseases producing characteristic rust-orange powdery pustules on leaf surfaces. Each rust species infects a particular host plant. Leek rust, allium rust, and mint rust are among the most common in vegetable and herb gardens. Rust weakens plants and causes premature leaf drop in severe cases.
Anthracnose
A group of related fungal diseases (primarily Colletotrichum species) causing dark, sunken lesions on fruits, leaves, and stems. Each strain is host-specific. It is most destructive on ripening fruits and berries, with infected produce rotting rapidly. Spores spread via water splash and are most active in warm, humid conditions.
Black Spot
A fungal disease primarily associated with roses but also affecting cane fruits in the garden (as related Diplocarpon species). It thrives in warm, wet conditions and can cause severe defoliation. The fungus overwinters on fallen leaves and infected canes, and spreads by rain splash in spring.
Verticillium Wilt
A soil-borne fungal disease caused by Verticillium dahliae and V. albo-atrum that colonises the vascular system similarly to Fusarium wilt. It affects a very wide range of plants and can persist in the soil for many decades. It is most severe in cool soils in spring and autumn, and particularly problematic on strawberries and stone fruits.
Deer
Deer can cause severe damage to gardens overnight, browsing a very wide range of plants. They are most active at dusk and dawn and are more destructive in late winter and early spring when natural forage is scarce. A single deer visit can destroy beds that took months to establish, and once deer find a food source they return reliably.
Rabbits
Rabbits can cause substantial damage to gardens, particularly in early spring when other forage is limited. They target tender young growth and low-growing crops and a small family group can cause losses disproportionate to their size. They make clean, angled cuts — the opposite of the ragged tearing caused by deer.
Voles and Moles
Voles are small rodents that create surface and subsurface tunnels and feed on roots, bulbs, and tubers. Moles are insectivores that eat grubs and earthworms — their tunnelling can uproot plants but they do not eat plant material. Both are present in most gardens; voles cause the primary plant damage.