Flower Garden Pests and Diseases
Pests and fungus diseases of particular plants
Rust: fungus disease. Symptoms are raised, bright rust-brown spots on under-surface of leaves and on stems; leaves wither. Some varieties are resistant; consult catalogues. Spray thiram at two-week intervals from end of early summer to end of late summer. Remove badly infected plants and burn.
Aster wilt: soil-borne fungus disease which infects roots. Symptoms are wilting, then blackening of stems from base and browning of internal tissue of living stems. Wilt-resistant varieties are available; destroy infected plants, sterilize or replace soil.
Foot rot: soil-borne fungus disease which invades roots. Symptoms are blackening of base of stem, followed by sudden and total collapse of plant. Destroy infected plants, water soil round remaining plants with thiram or a copper-containing fungicide.
Leafminer: insect pest. Symptoms are wavy white lines on upper surface of leaves, in bad infestations leaves brown and wither. Hand-pick and spray with dimethoate; do not spray flowers.
Leafminer, see Chrysanthemum
Vine weevil: insect pest. Symptoms are leaves wilting for no apparent reason, fat cream-coloured grubs in corms and compost. Adults are black, 0.6cm (1/4in) long, with a long, two-pronged snout; they eat holes in margins of leaves. Hand-pick grubs, water compost with HCH (BHC), trap adults in small pieces of rolled up sacking or paper placed on the soil.
Earwig: insect pest. Symptoms are holes and ragged edges to petals and leaves, flowers may then be infected with. Nocturnal feeder; trap in flower-pots stuffed with straw or paper, placed upside down on tops of and spray plants and ground with trichlorphon or carbaryl.
Thrips: insect pest. Symptoms are small silvery streaks on leaves and buds, later turning brown. Thrips are tiny, yellow-to-black pests, known as ‘thunder bugs’, most frequent during hot, dry weather. Remove affected buds, and spray with malathion.
Hollyhock Rust: fungus disease. Spray thiram at two-week intervals from the end of early summer to the end of late winter. Remove badly infected plants and burn.
Leather-jacket: insect pest. Symptoms are roundish patches of beige-coloured grass, slowly enlarging during late autumn, winter and spring. Grass is killed. Leather-jackets are grey-brown, slowly-moving caterpillars found in top 2.5cm (1in) or so of soil. Mature size is 2.5-3cm (1 – 1-1/2in) long, adults are cranefly (daddy-long-legs). Water lawn with HCH (BHC) solution.
Fusarium patch: fungus disease (sometimes known as snow mould). Symptoms are pale yellow-brown patches of dead grass, edges sometimes fringed with white, fluffy growths. Disease most common autumn and winter. Remove infected areas, replace with fresh soil andor seed; water neighbouring turf with copper-containing fungicide.
Fairy ring: soil-borne fungus disease; symptoms are rings of toadstools in grass, 90cm (36in) and more in diameter. If grass within and around ring is dark green and does not die, spike 10cm (4in) deep and water with sulphate of magnesium at 60g in 4.5L per sq m (2oz in 1 gal per sq yd), two or three times at four- or five-week intervals.
If the grass has died completely within ring, leaving a bare patch, remove soil and turf to a distance of 60cm (24in) beyond ring and a depth of 30-45cm (12-18in); replace with fresh, or sterilize the same area, forked up, with formalin, using a dilution rate of 1 part formalin to 39 parts water, and applying 18L per sq m (4gal per sq yd). Cover for ten days, then fork soil and replant when smell of formalin has gone (about six weeks).
Bulb fly: insect pest. Bulbs grow and flower poorly, do not flower at all, or die and do not appear in the season following infection. Bulbs become soft and contain white maggots internally. Destroy such bulb’s and dust soil round remainingwith HCH (BHC) from end of late spring at two-weekly intervals until end of early summer.
Black-root rot: soil-borne fungus disease. Symptoms are yellowing leaves followed by withering, death of plant and blackening of roots. Destroy affected plants; rest soil for three years, or sterilize, or replace.
Stem rot: soil-borne fungus disease. Symptoms are yellowing of leaves which then die, main stem rots at base. Destroy affected plants; dust soil with fungicide containing mercury (calomel) and improve, or plant in different site.
Black-root rot, see Pansy; rust, see Antirrhinum (N.B., no resistant varieties of pelargonium).
Peony Blight: fungus disease. Symptoms are wilting of plant and death of young shoots at base of main stem, following browning. Remove affected parts where possible. Treat plants and soil round them with benomyl fungicide; dig up and destroy plants if they do not recover and plant new specimens in a different site.
Bud disease: physiological. Symptoms are stem just below flower bud shrivelling and turning brown; bud hangs down and does not open. Supply potash in spring; make sure plant does not run short of water or become waterlogged. Protect from hot sun after cold nights.
Eelworm: pest. Symptoms are twisted, narrow leaves, turning brown from base of plant and falling, stems swollen and splitting from base upwards, flowering poor or non-existent. Dig up plants in winter, use roots for, and destroy remainder of plant. Plant in different site.
Foot rot, see Aster
Thrips, see Gladiolus; black-root rot, see Pansy
Fire: fungus disease. Symptoms are blackened patches on leaf tips and later rest of leaf, and on buds and flowers; bulbs have blisters on the outside. Destroy badly infected plants; spray remainder and soil with captan or thiram, avoiding flowers. Following year start spraying when growth 2.5cm (1in) tall, until flowers unfold.
Leaf-midge: insect pest. Symptoms are thickened leaves, rolling inwards from margins. Plants small and poorly flowering. Pick off infested leaves and spray plant with dimethoate early in late spring, the middle of late summer and in mid-autumn.
Flea-beetle: insect pest. Symptoms are small round holes in leaves of seedlings and very young plants; tiny, hopping irridescent beetles present. Dust derris or HCH (BHC) on to leaves when dry.
Wire-stem: fungus disease. Symptoms are brown, constricted stem near base, plant stunted if not killed. Destroy infected plants; use sterilized soil for seed compost or seedbed. Dust seed with captan or thiram.