Late July/August is the time to be extra vigilant, especially when checking potatoes and tomatoes.
If the weather's mild, wet and humid, these are ideal conditions for a deadly attack of phytophthora infestans (late blight) for which there is no chemical cure.

The pathogen's carried on the wind and first indications that your plants have been attacked are dark patches on leaves with a white powdery mould - particularly underneath.

If left unchecked, the plant will be turned into a rotting mes...