Xiphinema americanum The Dagger Nematode Damage to Corn.   Dagger nematode is a common associate of corn in the United States.  Crop losses are hard to measure, however, because the nematode usually occurs with other known pathogenic species. Biology.   X. americanum is a long, didelphic nematode up to 2 mm long.   There is speculation that the life cycle takes a year or more to complete. Ecology.   Dagger nematodes are found in sandy soils. Symptoms.  Damage to other crops.   Xiphinema has a wide host range, being an important pest in many other crops. Control.   Annual cultivation of fields may disrupt the life cycle of this nematode, resulting in reduced populations.