Why did daylillies die?


In the same bed, one of my daylillies just bit the dust. It had been “shrinking” over the last few months and only a few small leaves left. I pulled it from the ground to find the rootball had seemed to rot, or rather, had turned into this hunk of what looks like wet sawdust. On closer examination, I found a few teeny (and I mean teeny) fast-moving white worms I have never seen before.

As soon as they were exposed to sunlight, they’d burrow quickly back into the rootball. I found these little worms in the soil below the plant, too.

Do you know what they are and what I can do about them? I have read about a pest called gall midge, but I don’t know if they are in Hawaii. Do you think a systemic insecticide might help?

There is no need for systemic insecticides; the worms you see are not the larvae of the Hemerocallis gall midge.

This midge is a small fly which has been a pest of daylilies in Europe for several decades. It was found in British Columbia, Canada, in the summer of 2001 and is now reported to be in the Northwestern United States but not in Hawaii.

In addition, the larvae of the gall midge feed on the developing flower parts causing deformation. Infested buds may contain up to a hundred or more small white legless larvae that measure about 0.12 inches in length.

The worms you are seeing are feeding on the decaying bulbs; they were probably attracted to the bulbs because of the decay rather than causing the decay.

The daylilies you described may have a simple case of root rot (or bulb rot) due to prolonged wet soils. This year a number of plants, that are normally healthy, have died because of an overabundance of rainfall. The best course of action is not to plant daylilies in that same bed for at least three years.

For those growing daylilies, be aware of a relatively new disease called daylily rust. It came to Hawaii in 2002. The disease affects the leaves and the flower stalk. They become covered with a yellow to orange powder, which is the spores of the rust fungus. Different varieties of daylilies have varying degrees of susceptibility to the rust disease. With susceptible varieties the entire leaf will shrivel up and die. The spores do not affect the bulb itself even though they may be present on the surface. For more information on this disease, access New Pest Advisory No. 02-02 (March 2002) titled “Daylily Rust,” on the Hawaii Department of Agriculture website at www.hawaii.gov/hdoa.

To help readers familiarize themselves with botanical terms, here are two basic divisions in the plant kingdom:

Dicot or dicotyledon are flowering plants whose seeds have two parts, known as cotyledons or seed leaves. Beans are a good example. The veins in the leaves of dicot plants are characteristically branched or netted. Their flowering parts are in multiples of four or five. The root system is considered a taproot with a tapering root that grows downward and has other roots sprouting laterally from it.

In contrast, monocots or monocotyledons are flowering plants whose seeds have one part as in corn, hence the name mono. Their leaves have parallel veins with flowers parts in multiples of three. The root system is fibrous. Corn, rice and wheat are examples.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.

 

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