Diseases

Many diseases are spread by water, be that from rain or watering the crop. Careful watering can help reduce spread of disease. Most diseases also favour humid conditions so try and maintain a good airflow through your crop by ventilating to allow air change to take place.

A number of the more common diseases encountered under Irish conditions are listed below.

Botrytis (Grey mould)

• This is a furry grey mould which will invade the plant where wounds occur.
• A humid atmosphere encourages botrytis to develop so good ventilation is important to create air movement and keep foliage dry. High humidity will encourage spores of the disease to develop on the ripening fruits causing ‘Ghost Spot’ on tomatoes.
• Lettuce crops can suffer from this disease, mostly in spring and early autumn.
• Water plants early in the day, to avoid build-up of humidity at night-time.
• If this disease becomes a major problem your local garden centre or garden shop may have some specific control products available. (Follow manufacturer’s directions and safety instructions.)

Tomato Blight

• Tomatoes are in the same family as potatoes and can be affected by the same blight disease.
• Blight is a bigger problem on older heirloom varieties than on the newer F1 hybrids.
• Control humidity in the greenhouse.
• Practice good hygiene.
• Use a clean water source.
• Destroy all debris from previous crops.
• Blight is more likely to be a problem on outdoor tomato crops.
• To protect the crop, your local garden centre or garden shop may have some specific control products available. (Follow manufacturer’s directions and safety instructions.)

Damping-off 

(Rhizoctonia, Phytophthora, Pythium)

• Root rots are a common cause of seedling loss with blackening of roots or stems.
• Use quality disease free compost.
• Avoid over-watering and ensure soil or growing medium is free draining.
• Use fresh soil each year to avoid carry-over of these diseases.

Powdery Mildew

• Powdery mildew is common on glasshouse crops, especially cucumbers and strawberries.
• It will appear as a white fluffy growth on the upper surface of leaves. If noticed early remove infected leaves and try to reduce the airflow through the house to prevent its spread. 
• To protect the crop, your local garden centre or garden shop may have some specific control products available. (Follow manufacturer’s directions and safety instructions.)

Blossom end rot

• Not technically a disease but a very common problem for home growers.
• Calcium is required for normal cell growth. When fruit is growing rapidly it may be deprived of calcium when there is a shortage of calcium in the soil, if there is too little moisture available or when plants are waterlogged at the root. If plants are short of calcium a lesion can form at the blossom end of the fruit and as the fruit develops this lesion becomes an enlarged brown rot.
• This problem can generally be avoided by regular even watering.