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CONTENTS
[Return to Nematode Identification] |
Ring nematodes (Criconemella xenoplax) are migratory ectoparasites (Fig. 1) related to pin nematodes but they are slightly longer and wider. They have a larger stylet and are easily distinguished by distinctive coarse ridges (annulations) around the body. Ring nematodes are not easily recovered by some soil extraction methods and may not be reported in accurate densities on some test reports. Thus, ring nematodes may be more prevalent in mint than previously believed. Recent work in the Willamette Valley of western Oregon has identified several fields with moderate to high densities of ring nematodes. Ring nematodes have a wide host range that also includes many woody plant species.Life Cycle The life cycle takes 25-35 days (Seshadri, 1964). After feeding for several days on roots, females deposit single eggs every two to four days (Thomas, 1959). Second stage juveniles (J2) hatch from the egg in 11-15 days, molt to J3 in three-five days which then molt to J4 in four-seven days to become adults five-six days later. Adult females begin to lay eggs in two-three days (Seshadri, 1964). Males are almost never observed. Ring nematodes increase more in coarse than in fine textured soils. Optimum conditions for reproduction include a pH near 7 and soil temperatures between 75 and 80 F. Ring nematodes appear to be sensitive to low soil moisture and low pH. Feeding BehaviorUnlike most soil nematodes, ring nematodes move using waves of elongation and contraction which pass from head to tail, similar to an earthworm. For this reason, they are more sluggish than other nematodes and do not extract well in procedures which require active migration, such as Baermann funnel procedures. Favorable feeding areas on roots appear to be found by trial and error. Once a suitable feeding site is located, the lips are held close to the root and the stylet makes short, deliberate probes as the head moves side to side and up and down. After a one or two minute interval, the stylet is inserted into the chosen epidermal cell, and all other body movement ceases. In some cases, the long stylet may allow the nematode to feed on deeper cortical cells while the nematode remains outside the root. Feeding in the same location may occur continuously for 18 hrs or more (Thomas, 1959), up to eight days in one instance (Sijmons et al 1994). Cell walls in the feeding area become modified to facilitate transport of cell contents towards the stylet for consumption by the nematode (Sijmons et al., 1994). Symptoms and Effects on Plant GrowthAlthough ring nematodes are found on a wide diversity of crops, few studies have been initiated to determine the potential for yield loss. Ring nematodes often occur in high numbers in peppermint, but no studies have been conducted to determine what damage they cause to mint. Although they do not appear to be strongly pathogenic on many plants, ring nematodes play an important role in peach tree short life disease. In carnation, blooms and root systems are reduced and top growth is stunted. |
