Look for
Dark brown or black patches surrounded by paler areas on wilted and curled leaves. As the plant weakens, stems can also be affected showing brown discolouration and decomposition of the whole plant soon follows. Underground potato tubers suffer from an all over reddish brown rot that destroys the vegetable and has a foul odour. The fruits on a tomato will soon start rotting after the leaves become infected.
Plants affected
- Potatoes, tomatoes and other members of the Solanaceae family.
About
- Potato blight and tomato blight are both caused by the same fungal disease.
- Once the fungus takes hold it rapidly spreads rapidly by wind-borne spores.
- Tomatoes grown under glass will be less likely to succumb as the blight spores do not easily get inside greenhouses.
- The fungus spreads easiest when weather conditions are above 10 degrees centigrade and when there is high humidity in the air.
- Tubers carrying the disease which are not incinerated can become ‘Primary Infectors’ if they are replanted and conditions are ideal for the fungus.
- Periods of hot dry weather can subdue and delay potato blight symptoms.
- Blight cannot survive in soil or fully composted plant material. It over-winters in living plant material and is spread on the wind the following year.
- The most common way to allow blight to remain in your garden is through ‘volunteer potatoes’. These are tiny potato tubers which survive over the winter in the soil or the compost heap and shoot up again in the following spring.
Treatment
Chemical
There are a number of copper based fungicides, including Bordeaux mixture which will have some effect. They mainly work in a preventative way so waiting until the first symptoms appear may be too late.
Note: It is important to read manufacturer's instructions for use and the associated safety data information before applying chemical treatments.
Organic
- Regularly observe crops to check for damage and remove all affected plants immediately and incinerate.
- Keep weeds under control that could be alternative host plants e.g. Deadly Night Shade.
- Avoid growing at times of year when weather conditions are favourable for the fungus.
- At the first sign of infection, cut down all the tops of potato plants (known as the haulms) and burn or fully compost them. Then leave the tubers in the ground for a few days before lifting them to allow any blight spores on the soil surface to die off.
- Do not compost infected or unused tubers.
- Tomatoes should be harvested as soon as blight becomes apparent even if they’re still green (make chutney!)
Preventing Further Infection
- Grow resistant varieties such as: Potatoes ‘Axona’ or ‘Mira’ and Tomato ‘Ferline’.
