An Ecological Study of Xiphinema Americanum Cobb in an Ornamental Spruce Nursery

Two seasonal population peaks of Xiphinema americanum were observed in an ornamental spruce nursery. One cycle extended from April to August and the other from September to January. These peaks became less obvious in the larvae and non-gravid adult populations as sampling depths increased. The gravid adult population, however, showed two distinct cycles at all sampling depths. Large numbers of nemas became tesselated and transparent in July; this was followed by a sharp decline in the nematode population. Eggs and third and fourth stage larvae were apparently the only stages to survive winter temperatures; adults disappeared at all sampling depths from 0-50 cm even though the soil was never frozen below 33 cm and the temperature never dropped below 1° C at 46 cm. There appeared to be an antagonism between X. americanum and Criconemoides xenoplax since C. xenoplax declined and X. americanum increased in number in two ornamental blue spruce plantings.