Lily

A bright scarlet beetle (Lilioceris lilii) whose adults and larvae feed on lily foliage and can strip a plant to bare stems within days. The larvae cover themselves in their own excrement, appearing as slimy brown blobs on leaf undersides.

Watch for: Vivid red beetles on leaves and stems from first spring growth, chewed leaf margins, and slimy brown lumps beneath the leaves.

Prevent: Check plants twice a week from the moment shoots appear - early interception is far more effective than any treatment once numbers build. Clear debris around plants in autumn where adults overwinter.

Treat: Hand-pick adults into soapy water (they drop when disturbed, so cup a hand underneath) and wipe larvae off leaves. Neem gives some control on larvae; heavy infestations may need repeated attention through the season.

Squirrels, chipmunks, voles and mice are the wildlife that competes with you most directly for a crop. They take ripening nuts, seed and fruit off the plant, usually before you judge it ready, and cache what they do not eat. They also dig up freshly planted bulbs and sown seed, and voles tunnel in to gnaw bulbs and roots underground through winter. They climb anything, they know exactly when a crop is ripe, and a determined pair can clear a small tree or a new planting in a few days.

Watch for: Chewed husks, shells or hulls scattered under the plant, fruit and nuts vanishing as they ripen, and gnawed or half-eaten windfalls. On new plantings: freshly dug holes and scattered soil, bulbs missing or gnawed, dug-up seed rows, vole runways under the mulch, and gaps in spring where you know you planted.

Prevent: For a crop on the plant, timely and frequent harvest is the real defense - gather daily through the ripening window rather than leaving anything to hang, and pick slightly early to finish indoors where the crop allows it. Net or bag what you can reach. For bulbs and sown seed, lay wire mesh or hardware cloth over the planting, plant deeper, use buried wire baskets, and clear away the papery tunics and debris that advertise a fresh planting. Trunk baffles slow climbers on isolated trees, clearing jumping routes from nearby trees and roofs helps, and removing brush cover reduces the rodents sheltering nearby.

Treat: There is no rescue for what has already been eaten, so this is a prevention problem. Re-cover disturbed plantings with mesh promptly, replant losses inside cages, and trap or exclude persistent diggers where that is legal locally. On a large tree, accept that you will share the crop and concentrate on gathering promptly.

Lily bulbs lack the protective papery tunic other bulbs have, which makes them particularly attractive. Plant in wire baskets or hardware-cloth cages with sharp grit around each bulb, and trap where vole runs are active.

Bulb rot is not one organism but a group of soil fungi and water molds - Fusarium, Rhizoctonia, Pythium, Phytophthora and others - that live harmlessly in most soils and turn destructive only when the ground stays saturated. A bulb is a swollen food store with no way to shed water, so once the soil around it is airless the scales suffocate, soften and are invaded, and the whole bulb goes brown, mushy and sour-smelling. Dormancy is the dangerous season: a resting bulb draws almost nothing, so it can sit in cold or hot wet ground for weeks with nothing drying it out. The damage is underground and invisible, so the first sign is usually a clump that simply never comes up.

Watch for: A planting that fails to reappear at all in its season - the commonest symptom and the last one noticed. Shoots that emerge thin, yellow and stunted, or start up and then collapse. Clumps thinning year on year in the low, wet corner of a bed while the same bulbs thrive on higher ground. Lift a suspect bulb and look: a healthy one is firm and heavy with clean pale scales, a rotting one is soft, brown or blackened, often slimy between the scales, and smells sour. Roots gone brown and stringy rather than firm and pale. Standing water, or a dark permanently damp patch of soil, over the planting after rain.

Prevent: Drainage does nearly all the work. Plant bulbs in ground that drains freely and never stands in water, and where the soil is heavy plant on a raised bed, a berm or a slope, or grow them in containers - a pot needs an open hole and must never be left standing in a full saucer. Set bulbs at the depth the plant actually wants rather than deeper, and keep mulch pulled back from the neck. Water the soil rather than the calendar, and cut watering right back through dormancy when the bulb is not drawing. Never plant a bulb that is already soft, bruised or mouldy, and do not dig or plant in soggy ground.

Treat: Nothing brings rotted tissue back, so the work is triage and drainage. Lift the planting, sort the bulbs, and bin every one that is soft, discoloured or foul-smelling rather than composting it. Keep only bulbs that are firm all through, trim any small damaged patch back to clean tissue, let the cut surfaces dry in the air for a day, and replant into free-draining ground or fresh mix somewhere the water moves away. If the same spot rots bulbs every year, do not replant it - raise the bed, open up the soil, or move the planting and grow something else there.

Aphid-transmitted viruses that cause mottled, streaked or twisted foliage and progressively weaker, distorted flowers. Tiger lilies are often symptomless carriers that infect neighbouring hybrids.

Watch for: Yellow mottling or pale streaks along the leaves, twisted growth, and flowers that break colour or deform.

Prevent: Control aphids, buy virus-free bulbs from reputable suppliers, and keep tiger lilies well away from prized hybrids.

Treat: There is no cure - remove and bin affected plants (never compost them) so they do not act as a reservoir for the rest of the bed.

A fungal disease of wet, crowded conditions producing oval brown or orange spots on leaves that merge until the foliage collapses, sometimes taking the flower buds with it.

Watch for: Round to oval tan-brown spots on lower leaves after wet weather, spreading upward; grey fuzz in prolonged damp.

Prevent: Space plants for airflow, water at the base rather than overhead, and remove all dead stems and fallen foliage at the end of the season.

Treat: Remove affected leaves promptly and improve air movement; in persistently wet seasons a garden fungicide applied early can slow spread.