Xiphinema americanum The Dagger nematode Damage.   Dagger nematodes cause root stunting and tip galling.  In addition, as virus vectors they can be damaging at very low population levels. Biology.  Dagger nematodes are migratory ectoparasites (piercing the roots to feed) found only in soil.  Ecology.   Xiphinema americanum is widely distributed, especially in sandy soils. Symptoms.  Enlarged root tips and feeder roots may occur which could result in a 'witches' broom' effect on the root. Yields may be reduced when nematode populations reach high levels.  Damage to other crops.  Xiphinema americanum has a wide host range  including strawberries, soybeans, forest trees (spruce, pine, etc.), perennial orchards as well as grape.  Control.  Chemical control is effective in protecting new roots from nematode feeding until they can become established. Links and References.  Grape nematode (Dagger). Oregon State University.