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Most of the trials and tribulations affecting other garden plants also affect those under glass, only worse, because the increased warmth and close atmosphere will encourage them. There are, however, many which are especially annoying in the greenhouse, the most common of which are listed in the table below.

Common Greenhouse Problems

Symptoms Cause Remedy
Rotting flowers and buds, grey mould or discoloured blotches on leaves, stems and sometimes fruit Botrytis Spray with Benlate. Remove affected parts. Reduce watering and watch humidity in cold weather.
Powdery dust on leaves, new shoots distorted Powdery mildew Spray with Benlate.
Web-like covering on leaves which look dry and discoloured, red dust-like deposit Red spider mite Mist regularly and increase humidity.
Stems rotted off at base Basal stem rot No cure – pull up affected plants. Do not overwater.
Red pustules on leaves Geranium or carnation rust Spray with propiconazole. Do not use on edible crops.
Yellow mottling or discoloration Virus Noen. Pull up and burn.
Papery patches on leaves Sun-scald Increase shading in sunny weather.
Tiny, white, moth-like insects Glasshouse white fly Spray regularly with an insecticide suitable for use under glass.
Yellowing leaves which drop Overwatering Reduce water, especially in winter.
Woolly-looking insects Mealy bug Spray with an insecticide suitable for use under glass.
Clusters of green or brownish insects on shoots Aphids As above.
Patches of scale on stems Scale insects As above.
Plants or seedlings drawn up Insufficient light Try to improve conditions if possible.
Roots eaten off Leatherjackets, millipedes, vine weevil grubs, wireworms, chafer grubs, cutworms Usually occurs in greenhouse soil but can happen in pots if they are in contact with soil. Treat soil or compost with a soil insecticide. Vine weevil grubs can be controlled with beneficial nematodes.
Petals eaten Earwigs Trap in pots filled with hay or finely shredded newspaper.

Note: Most common insects are attracted to yellow colouring. Many insect pests can be trapped successfully by suspending the yellow sticky cards readily available from garden centres amongst the foliage of glasshouse plants. These should be positioned before signs of infestation, and removed when the surfaced becomes thickly covered with trapped insects.

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