Pine Wilt Disease
by David Steg on 10/13/14
| Common Name: | Pine Wilt |
|---|---|
| Pathogens: | Pine Wood Nematode Bursaphelenchus xylophilus, together with related stresses and/or microorganisms |
| Common Host: | Pine Pinus spp Figure 19 - Generalized life cycle of the pine wood nematode. |
| Significance: | In recent years the pine wood nematode has received considerable attention in Florida as well as the country as a whole. The pine wood nematode was initially thought by many to have been introduced into the United States. This caused considerable alarm since native tree species often have little innate resistance to introduced pests. However, recent evidence indicates that it is likely that the pine wood nematode is a native of North America. In Japan, where it may very well have been introduced, the pine wood nematode is responsible for the death of pines over vast acreages over the past 30 or more years.Today the pine wood nematode is known to occur throughout Florida and in much of the U.S. It has been detected in the recently dead and dying stems and branches of several species of pines. The role of the pine wood nematode is the death of the trees (pine wilt) is still not well understood. In the United States, it appears that, in general, the pine wood nematode is not a primary, aggressive killer, but rather a secondary, contributing factor, perhaps working in concert with other microorganisms to finish off trees which have been injured or stressed by environmental or other agents. However, the pine wood nematode has been reported as a primary pathogen on certain exotic (introduced) pine species, and it appears likely that it may play a similar role on native pines in certain situations. |
| Recognition: | Trees affected by pine wilt characteristically exhibit a fairly rapid foliage color change from green to yellow-green to reddish or brown. This usually occurs during the mid to late summer. A key feature of this disease phenomenon is a concomitant marked reduction in resin flow within the sapwood of symptomatic trees (determined by cutting a branch or into the trunk for examination). Death of affected trees is rapid. Pine wilt symptoms are frequently related to and often follow severe injuries or stresses sustained by pines such as lightning, fire, construction damage, soil compaction or drought.Pine wood nematodes are small (less than 1 mm in length) and difficult to see with the unaided eye. However, placing small segments of suspect branch or wood samples in a jar of water overnight (samples submerged) provides a useful detection aid. If the nematode is present, hundreds to thousands of the nematodes will swim into the water and can be seen readily as clouds upon swirling the container (laboratory confirmation of specific identity is advised). |
| Infection Biology: | The pine wood nematode reproduces and proliferates rapidly (one generation every 4-5 days with each female laying up to 80 eggs) in the resin ducts within the wood of infected, dead and dying pines. It is in just such pines that the larvae of the nematode's insect vectors (various longhorn beetles; Coleoptera, Cerambycidae) develop and mature. Mature longhorn beetles emerge from the dean and dying trees in the late spring carrying the dispersal stage of the pine wood nematode. The nematode is introduced into the xylem of susceptible pines as the beetles strip the bark from branches in order to feed. Following its maturation feeding the adult female beetle finds a suitable declining pine in which to lay her eggs. If the pine is infected with the pine wood nematode the cycle is set to repeat. |
| Control: | Practical controls for the pine wilt disease and its apparent causal agents (Bursaphelenchus xylophilus, etc.) are lacking. Where practicable, keeping insect vector activity at a minimum by destroying breeding habitat (fresh cut or fallen logs, recently dead or dying trees, severely injured trees, etc.) would presumably be advisable. |
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