Annual cycle of root nematodes on white clover in pasture

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Abstract
Fortnightly sampling for H. trifolii cysts in soil, larvae in soil, and larvae and females in roots was carried out in Southland from September 1973 to April 1975. Cyst numbers were 50 000-70 OOO/m2 during the periods of nematode dormancy in December-January and March-April. A brief reproductive period occurred in January-February. Female nematodes next appeared in the roots in significant numbers in September-November, although larvae began emerging from cysts in May. Invasion of clover by H. trifolii corresponds with increasing clover growth rates, but emergence of larvae from cysts may not. In the annual cycle the spring mortality of larvae in roots, the maximum larval density of about 1000/10 g roots, and the two reproductive cycles are similar to those previously reported for a yellow-grey earth in the Wairarapa. However, the total cyst count is lower than in the Wairarapa (70 000/m2 cf. 180 000/m2) and the period of summer dormancy is 8 instead of 14 weeks.

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