So much for the actual; water-lilies and marginal plants are susceptible to few ailments. Nymphaeas may sometimes suffer from a fungus disease of the genus Cercosporae. This is comparatively rare, but when the fungus is present, spots will develop on the which became dry and crumpled. A light spraying of Bordeaux mixture, applied every other day at half the strength directed for other plants, is the only remedy. The affected should, of course, be removed. But do not mistake the natural decay of leaves for this fungus. If healthy leaves are rising to the surface and developing as others are dying off, then this is only evidence of the natural cycle of events. And, of course, once autumn frosts have arrived you can expect the Nymphaeas to die back quickly.
A peculiarity of some water-lilies is the phenomenon known as fasciation. An individual plant may grow and flower normally for a number of years. Then, for no apparent reason, it ceases to bloom and instead of producing leaves of usual size, it throws up a much larger number of tiny leaves. If you lift the plant you will discover, instead of just a few separate and well-defined growing points, a jungle of leaves and shoots growing all over the tuber. Fasciation is rare, but when it occurs there is only one solution. Remove any eyes or shoots that appear normal. These can be planted and should grow into ordinary tubers which will flower and produce leaves of the usual size. The original tuber can be discarded.
Reverting to type is a tendency that you may notice with some of your variegated marginals. In amongst the variegated foliage plain greenmay develop. Given time, the whole plant may revert to the plain colour of its ancestors and you will have lost the variegated species with which you began. The only thing you can do is cut out the plain as they arise and hope that the rest of the plant will remain true to type. The fact that the variegation on the leaves of his pseuda-corus variegatus, for example, may lose some of their lustre, the green and bright creamy stems taking on a duller appearanceat the end of summer, is not evidence of reverting to type, but only of the ageing process of the leaves. Should any straight leaves appear on Juncus effusus spiralis, they also should be ruthlessly cut out.