Plant Doctor Archive

Daylilies dying off

I HAVE a garden full of daylilies and in some areas the plants are dying off. The backs of the leaves develop fine rusty-looking channels, then the leaves turn yellow and die. Several months ago I found aphids down in the inner leaves and sprayed with Orthene. Some plants I chopped off and sprayed and these have come away again but are now showing dryish tips again. I am now wondering if it is mites or some soilborne disease.

DAYLILIES are generally not prone to pest or disease problems, but, in certain conditions, there are several fungus diseases, including rust and leaf spots that can affect them.

The symptoms you describe suggest fungal disease rather than mites or aphids. The cool, wet weather we experienced in spring and early summer have encouraged fungal problems in plants that are normally relatively disease free.

Clearing out the affected leaves as you have done is a good idea, as is cutting out about two-thirds of all the foliage in winter to reduce the risk of disease overwintering and to encourage healthy new growth in spring. Now that the weather has improved, you may find the problem goes away and new growth is disease free, but you could spray with a fungicide such as Bravo, Fungus & Mildew Spray or Fungus Fighter. Follow the label recommendations.

Daylilies do best in free-draining soil, exposed to lots of sun and fresh air and are more likely to suffer disease if shaded and sheltered by nearby shrubs or if their leaves remain damp for long periods. So it may pay to prune nearby shrubs to increase air flow and exposure to sun, if necessary.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.