Very high level resistance to powdery mildew in melon and cucumber are very often linked to leaf necrosis phenomena appearing especially during periods of short days and low light (spring, autumn). Thus, against the background of very early crops, rare varieties exhibit leaves that show:

- localized lesions of irregular shape, chlorotic to necrotic (figure 1);
- generalized inter-vein dryness (figure 2).

The manifestation of this non-parasitic problem is quite rare now because breeders have become accustomed to ruling out it during their breeding programs for resistance to powdery mildew. Faced with this problem, it will therefore be impossible to put in place any measure to control it.

Note that the symptoms of crown blight are quite comparable to those caused by another physiological disease: scorch leaf.