Posted by: Curtis Utley, Jefferson County Extension Plant Diagnostic Clinic
Have you ever seen an established pine in your neighborhood just up and die? I received some branch samples last week from a Scots pine (Pinus sylvestrus) that “just died this fall”. Now this is alarming to a homeowner and a diagnostician alike. There are many possible causes for woody plants to die outright.
|Dead Pinus mugo.|
One of the causes of rapid death I screen for in exotic pines is the presence of pine wilt nematodes (Bursaphelenchus xylophilus). Exotic pines are those species not native to North America such as: Scots (P. sylvestrus), Austrian (P. nigra), mugo (P. mugo) , and red pine (P.densiflora).The nematodes are vectored to perfectly healthy pine trees during maturation feeding by the pine sawyers (Monochamus spp.); long horned beetles which carry the nematodes within their bodies from an infested pine tree the beetles, as a grubs, called home the year before.
|Wood chips bubbling in a beaker|
The screening process starts by taking branch samples cut close to the trunk, or better yet, trunk wedge samples. These samples are cut into ¼” inch cookies. These cookies are then cut into tiny blocks. The cubes are then put into a beaker full of distilled water and air is bubbled through the water and chips overnight. The next morning I pour the wood soup through a #45 sieve stacked on top of a #325 sieve.
|Wood chips poured on top of a #45 sieve stacked on top of a #325 sieve.|
|Material trapped by #325 sieve.|
|Petri dish containing material trapped by #325 sieve.|
All of the larger wood material is captured on the #45 sieve while the nematodes, if present, are washed through and captured on the #325 sieve.
All of the material captured on the #325 sieve is then transferred to a Petri dish and observed microscopically. If nematodes are present they can be seen swimming through the aqueous saw dust. Pine wilt nematode is confirmed by the structure of the male genitalia.
Pine wilt nematode Bursaphelenchus xylophilus. Sandra Jensen, Cornell University, Bugwood.org