OREGON H.J. Jensen December 1960 AND Plant Pathology Department ORNAMENTAL Vol. 4, Issue 3 Oregon State College NURSERY DIGEST Pages 1,2 Corvallis, OR

EXAMINE CLEMATIS ROOTS FOR NEMATODE INFESTATION

Clematis, like many other flowers, has its share of mutilating pests and disfiguring plant diseases. One of the most devastating pests is a root knot nematode. Meloidogyne hapla, which commonly afflicts this choice flowering shrub wherever grown. The first sign of imminent disaster is usually pronounced stunting which during warm weather is accompanied by excessive wilting. Frequently these symptoms are associated with chlorotic foliage. In general, however, foliage symptoms alone are not necessarily specific for root-feeding nematodes, but do indicate the probability of a disorder due to activities of these pests.

A much more accurate diagnosis is made by examining the root system. If small, bead-like swellings occur on roots, root knot nematodes are most likely responsible. Verification can be made easily by routine microscopic examination. These swellings, usually called "galls" or "knots," vary somewhat in size depending upon the population density and age of nematodes in root tissues. A recent invasion of nematodes is hardly noticeable because plant tissues have barely had time to react to this penetration. By the time nematodes complete their lifespan, galls are very conspicuous, and may contain several white, pear-shaped objects which are the adult females. Each female may produce 300 eggs from which hatch a new generation of young nematodes. Since these pests complete a life cycle in approximately two months, vast numbers build up rapidly during a single year. Continuous reproduction is greatly accentuated when a longlived plant like clematis is involved.

Sale of infected plants spreads disease

Not only is the sale and growing of nematode-infected clematis unfortunate from the standpoint of worthless plants, but inadvisable because such plants introduce this pest into the soil and jeopardize many other kinds of plants. This is due to the pest's amazing adaptability to any usual environmental or soil condition and to a host range comprising more than 2,000 kinds of plants. Once infected clematis establishes this pest in the home flower garden, greenhouse, lath-house, nursery, or windowbox, the following consequences are likely to occur:

1. The pests will eventually leave the dying clematis, wander about in the soil, and soon attack a great variety of plants growing in the area or remain inactive in soil and attack plants grown there in the future. 2. Effective control measures require soil treatment in absence of plants. Since nematocides (materials used to kill nematodes) are rarely used on established plants and are most effective in barren soil, the entire area must be returned to seed-bed condition for best results. 3. Best available control measures cannot be guaranteed to eliminate these pests because some nematodes manage to escape lethal concentrations of nematocides.

Numerous methods of control including hot water and chemical soaks have been and are being investigated. Unfortunately, no material or method, has given complete eradication. Thus the best current advice is to avoid becoming a disappointed owner of diseased clematis plants. Examine the roots of planting stocks for nematode galls especially if the clematis is a "bargain."

Clematis roots severely infected with root-knot nematodes look like this. Arrow is pointing to one of many galls. Insert shows mature female root-knot nematode magnified several times.

Oregon Ornamental and Nursery Digest was published from 1957 to 1975 by the Agricultural Experiment Station, Oregon State University, Corvallis.

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