New Ways of Managing Plant-Parasitic Nematodes Under Study - West Coast Nut


New Ways of Managing Plant-Parasitic Nematodes Under Study


Published: May 16, 2019

Andreas Westphal, Department of Nematology, University of California,
Riverside, Parlier, CA.

Walnut production is most productive on deep-rooting uniform soils with good water-holding capacity. Such soils are also conducive to infestations of plant-parasitic nematodes. Currently, the key pest of concern in walnut plantings is root lesion nematode (Pratylenchus vulnus). In California, this nematode is wide-spread in walnut producing areas and is estimated to be present in almost 85% of walnut orchards.

Because of the longevity of a walnut planting, even barely detectable nematode numbers can cause damage to the traditional rootstocks in the life span of an orchard. English and Paradox rootstocks are susceptible to root lesion nematode. Other nematodes, root-knot nematodes (Meloidogyne spp.), can cause damage to English rootstocks. The third species frequently present in walnut soil is ring nematode (Mesocriconema xenoplax) but its damage potential has not been as well documented as for the lesion and root-knot nematode.

Plant-parasitic nematodes entirely depend on their host plants to sustain themselves. They can injure root tissues directly, and also consume photosynthetic nutrients that otherwise would be used for plant growth and nut production. Trees of all ages are susceptible, but newly planted and young trees are especially sensitive. In addition, the so-called replant problem, a biologically-incited disease that is poorly understood, can hinder the establishment and growth of new plantings.

Nematode problems become most challenging when an old orchard is removed and replanted. Under these conditions, the succumbing trees may have left behind huge numbers of the soil-dwelling parasites without symptoms the grower associated with nematode damage. When the young trees are exposed to these high populations, they can be severely damaged. Soil sampling for nematode evaluation when replacing an orchard should be standard practice.