Control of Pests and Diseases

Cultural and Biological Control in Protected Environments

Damping off in SeedlingsThis is a particular problem when sowing seed indoors or under glass. Caused by several different fungi, this disease causes emerging seedlings to collapse, often submerged in a mass of white fungal growth. Cultural controlRaise seedlings in commercial growing compost, which is usually free of these fungi. Either use new pots and trays for raising seedlings, or wash them thoroughly and preferably also treat them with a disinfectant such as Jeyes Fluid. Never reuse pots and trays in which damping off has been a problem Sow seedlings thinly to avoid crowding Preferably use mains water for irrigating seedlings grown in pots and trays. Avoid overwater ingKeep seedlings well ventilated to reduce humidity

Botrytis or grey mouldGrey mould, caused by the fungus Botrytis cinerea, is a very common disease, causing a growth of fuzzy grey mould. It infects many plants, especially those grown under glass where conditions are humid. It will infect most ornamental plants. especially Chrysanthemum, Cyclamen, Pelargonium and PrimulaCultural ControlHygiene is very important, especially under glass. Remove dead and dying parts of plants promptly and dispose of them.Reduce humidity by improving ventilation Avoid overcrowding plants

Glasshouse WhiteflyGlasshouse whitefly is a common sap-feeding pest, affecting many houseplants and greenhouse plants including tomato and Chrysanthemum Whiteflies excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.Biological controlTiny parasitic wasps, Encarsia formosa, attack whitefly nymphs. It is important to introduce the parasite before plants are heavily infested as it needs time to take effect. Encarsia is killed by most insecticides so is incompatible with chemical control methodsCultural ControlHang sticky yellow sheets above or among the plants to trap adult whitefly

Mealy bugMealybugs are common sap-feeding pests that infest a wide range of houseplants and greenhouse plants including African violet and tomato Mealybugs weaken plants and excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.Biological controlAdults and larvae of the ladybird, Cryptolaemus montrouzieri, find and eat mealybugs and their eggs in confined spaces on the plants. Parasitic wasps (Leptomastix spp.) are also available for use against this pest.The ladybird and parasitic wasps need relatively high temperatures and so are only likely to be successful during May to September. They are susceptible to most insecticides so are incompatible with chemical control.Cultural ControlInspect new plants carefully before putting them in a greenhouse or conservatoryRemove dead leaves and prunings as they may have mealybug eggs attached