FOLIAR (BUD AND LEAF) NEMATODES

Aphelenchoides fragariae and A. ritzemabosi are the two foliar nematode species found in California. They can be both endoparasitic and ectoparasitic, depending on the host plant. Second stage juveniles hatch from eggs that are either contained within plant stem or leaf tissues, or on the surface of tissue layers within leaf or flower buds. Juveniles develop through the third and fourth stages to become adult males or females. After males copulate with females, the females lay about two fertilized eggs a day. These species appear to lay relatively few eggs: A. ritzemabosi has been found to lay only 20 to 30 eggs, although this may be an underestimate because it is difficult to observe the female throughout an entire life cycle. The life cycle is relatively short for phytoparasitic nematodes; for example, for A. ritzemabosi it is between 11 to 14 days at 13C to 23C. As with stem and bulb nematodes, some juvenile stages adapt to drying and may remain alive and be carried in dry plant parts including seeds. These species are active, rapid swimmers; they may also be washed off plants by heavy rain and thereby infest lower portions of the plant near the soil level.

Infection by Aphelenchoides species in ornamental and strawberry plants often results in the killing of either a flower or leaf bud, or a growing point that produces a "blind" plant. When an infected growing point is not killed and continues to grow, the stems, foliage, and other structures that develop from it are likely to be crinkled, distorted, or twisted. The penetration of and feeding on leaf tissue will cause leaves to crinkle, curl, and discolor in the interveinal regions. Strawberry fruits may also become malformed and discolored from foliar nematode infection.

Aphelenchoides fragariae on carnation
Aphelenchoides fragariae on fern
Aphelenchoides fragariae on African violet, healthy in center
Aphelenchoides fragariae on Easter lily
Aphelenchoides fragariae on strawberry

From: McKenry, M.V. and P. A. Roberts. 1985. Phytonematology Study Guide. University of California, Division of Agriculture and Natural Resources.

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