Wax plant

The disease develops in overly wet, poorly aerated substrate and attacks the roots and the base of the stem. The roots turn brown, rot and lose their bark, which slips off easily, and a dark, watery rot appears at the stem base. The above-ground part wilts, yellows and dies back despite moist soil – a characteristic symptom, because the damaged roots no longer take up water. Especially at risk are houseplants, succulents and cacti (from overwatering), and in the ground conifers, rhododendrons, ericaceous plants and strawberries on waterlogged sites. The process begins inconspicuously at the root hairs and root tips, which darken and disappear, after which the rot advances towards the framework roots and the root collar. Healthy, pale, active roots waste away — what remains is a dark, rusty-brown or blackish, watery mass, and the outer layer of the root bark slips off like a glove, exposing the discoloured central cylinder. In trees and shrubs, infection of the collar and the base of the trunk (stem-base rot) shows as a dark, often streaking patch, sometimes with oozing, and the bark there is moist and sunken; in conifers and rhododendrons, browning and dieback are seen from the bottom or from the centre of the crown while the soil is still moist. Characteristic is the nested (patchy) occurrence of symptoms in the bed — where water and the pathogen accumulate locally. It is worth distinguishing the two causal oomycete genera: Pythium mainly attacks seedlings and fine roots, causing damping-off and root rot in cool, wet substrate, whereas Phytophthora also attacks older, woody plants, framework roots and the collar, more strongly in warmer, water-saturated soil. Key for diagnosis is the contradiction of the symptoms: the plant wilts and looks 'dry', although the substrate is wet — this results from the destruction of the roots, not from a shortage of water.

On leaves, shoots and fruit a black, soot-like coating forms that can be partly wiped off with a finger. These fungi do not infect the plant tissue – they grow on the sweet, sticky honeydew excreted by aphids, whiteflies, mealybugs, psyllids and scale insects. The coating therefore appears exactly where these pests feed, and its main harm is that it masks the leaf blade, reduces photosynthesis and disfigures the plants. The symptom is often seen on citrus, lime, maple and on houseplants and greenhouse plants. The coating may be thin and cobweb-like or thick, crusty and dull black — depending on the fungus species and the amount of honeydew; on evergreen plants it can persist through the whole winter. A key identifying feature: after the blade is wiped, healthy green tissue emerges from beneath the black layer — sooty mould leaves no spots, necrosis or pitting, because it does not penetrate the leaf. The extent of the symptom is also characteristic: the soot settles where the sticky honeydew drips, so it appears not only on leaves but also on objects beneath the plant — the pavement, garden furniture, a windowsill or car bodywork — which in itself reveals pests feeding higher up. The sooty mould fungi themselves are dark-pigmented (melanised) saprotrophs, which is why the layer is deeply black. Direct damage to the plant is usually moderate — weakening through leaf shading, loss of vigour, poorer appearance and reduced market value of fruit or ornamental plants — but a dense, long-lasting coating on many leaves genuinely limits assimilation and growth. Sooty mould is best treated as a visible signal that a colony of sap-sucking insects is developing higher up on the plant (or on a tree above it).

Insects covered in a white, cottony, waxy coating, gathering in leaf axils, at the base of shoots and on the underside of leaf blades. They look like tufts of cotton wool. They suck sap, weaken the plant and excrete sticky honeydew, on which black sooty mould develops. A common pest of houseplants and succulents. Adult females are oval, soft-bodied insects about 2-5 mm long, with a pinkish or grey body hidden under wax, often bearing waxy filaments along the sides and at the tip of the abdomen. Males are tiny, winged and do not feed. In most species eggs are laid in white, cottony ovisacs (cocoons), from which mobile larvae (crawlers) hatch and spread across the plant, carrying the infestation to neighbouring specimens; some mealybugs (e.g. Pseudococcus longispinus), however, are ovoviviparous and give birth to live crawlers without a distinct ovisac. In the warm, dry conditions of homes and glasshouses mealybugs develop all year round, in several overlapping generations - which is why a single treatment is rarely enough. Feeding symptoms are stunted growth, yellowing, deformation and premature leaf drop, and under heavy infestation dieback of shoots; the black sooty mould on the honeydew further reduces photosynthesis and disfigures the plant. A separate form is the root mealybug (Rhizoecus), forming white, waxy clusters on the roots and inside the root ball - the plant weakens and wilts with no visible pest on the above-ground parts. Mealybugs are often attended by ants, which eat the honeydew and protect the colonies from natural enemies.

A soft scale whose females form brown, dome-shaped, strongly convex "cups" (3–6 mm) sitting motionless on shoots, twigs and leaf bases. They suck sap, weakening the plants, and excrete abundant honeydew on which black sooty mould develops, disfiguring leaves and fruit. It feeds on fruit trees (plum, peach), grapevine, ornamental shrubs and houseplants. It belongs to the soft scales (Coccidae), not to the true armoured scales — its brown shield is the sclerotized body of the female and cannot be separated from her. In the Polish climate it usually develops one generation per year. It overwinters as an immature larva (second instar) attached to shoots and twigs, in bark crevices and near the buds. In spring the larvae resume feeding and the females grow quickly, turning into the characteristic, hardening "cups". Beneath its shield the mature female lays numerous eggs — often from several hundred to over a thousand. The crawling larvae (so-called crawlers) that hatch from them, usually at the turn of June and July, spread out onto the leaves and young shoots, where they attach and feed; before leaf fall they return to the shoots to overwinter. Symptoms of infestation are weakened growth and dieback of twigs under heavy attack, sticky, glossy honeydew on the leaves and beneath the plant, a black sooty coating that hampers photosynthesis, and numerous ants feeding on the honeydew. The larvae and females cluster in the forks of twigs, on the undersides of shoots, at the base of the leaves and along the veins and leaf stalks.