b'Especially during hot weather the fungus can spread quickly. Some varieties are especially sensitive. In growing tunnels mildew can be avoided partly by preventing from arising. Aeration should be done by opening just the side that is out of the wind.Purple spot disease | ALTERNARIA ALTERNATA Test centre HoogstratenTypical characteristic of this type of fungous disease are thepurple spots which appear on the leaves of the attacked plants. These round spots, measuring 2 to 5 mm, are having a red or brown spot in the middle. Just a single spot on the stem of a leaf or a cluster of flowers will be enough to let it die.91'