Diseases and Insects of Myrica faya

Insects and pathogenic fungi collected in its native habitats have been tested for their biocontrol potential under quarantine.  Among the fungi, Ramularia destructiva, Nectria galligena, and an undescribed species of Cryophonectria have been found to cause damage to M. faya in the field in its native habitats and have been, or are being tested under quarantine in Hawai‘i.  Also, a leaf spotting species of Septoria, tentatively referred to S. myricae, is known to infect Myrica cerifera (waxmyrtle) in the eastern U. S. and was found capable of infecting M. faya as well, on which it can cause defoliation. 

      Branch galls (left, from Maderia) and cankers (right, from the Azores), and large trunk cankers, were frequently observed.   The cankers were found to be associated with a Nectria sp., referred to N. galligena.  Whereas no fungus fruiting bodies were found associated with the galls, it was considered likely that these were caused by Nectria as well.   Although N. galligena itself has a broad host range, it was not found on other woody species in areas where infection of M. faya was common.  The disease on M. faya may be caused by a host-specific form of N. galligena, although the fungus has not been evaluated experimentally.

       A perithecium (sexual fruiting body) of Nectria from bark canker tissue (left).  The Cylindocarpon state (imperfect state) of Nectria formed in culture (right).

       The fungus Ramularia destructiva frequently was found attacking growing shoots of M. faya throughout its habitats.   Diseased terminals typically curled around, sometimes in a complete circle.  The fungus produced white sporulating material on the diseased tissue surface as shown (right).  Whereas the disease caused by Ramularia was usually not severe, occasionally it was found to cause significant impact (middle), and more rarely to severely attack the entire plant, as shown on the young M. faya (right) in the Canary Islands.  The pathogen appeared to be specific to M. faya, as it was not found on any other plant.

   In addition to its occurrence on shoots, R. destructiva was occasionally observed infecting M. faya inflorescences in the Azores.

     Ramularia destructiva was cultured in pure culture (left).  Conidia (spores) of R. destructiva (right), with characteristic dark thickenings at the points where they were attached to conidiophores or to each other.  Other than observations of its activity in the field, this fungus has not yet been tested for its potential as a biocontrol agent.

    Among the insects, or insect damaged observed on M. faya in Madeira was a shoot tip mining caterpillar that hollowed out the pith of developing shoots (arrow) and destroyed the apical growing point, and a fruit boring caterpillar which destroyed the seed.  Both types of damage are thought to be possibly caused by the same insect, Carposina atlanticella.  More extensive work with potential insect biocontrol agents was carried out by entomologists and is reported elsewhere (Lutzow-Felling et al., 1995).

    A species, apparently undiscribed, of the fungus Cryphonectria was found in the Azores causing trunk cankers of M. faya.  Cankers caused by this species were not found on other trees, although neighboring chestnut trees were found with cankers infected by the related C. parasitica, the fungus responsible for widespread and devastating chestnut blight in the eastern U. S.  The fungus fruits on the surface of cankered bark, as shown on an inoculated M. faya stem in quarantine (left), producing long, sinuous spore tendrils as viewed with a hand lens (right).

     In hosts-specificity tests in quarantine in Hawai‘i, cut stem sections of several woody species were inoculated with Cryphonectria sp.   The fungus sporulated profusely on M. faya (left) and did not sportulate on most other species tested.  However, sporulation was observed on sections of kolea (Myserine lessertiana) in the family Myrsinaceae, an endemic Hawaiian tree.   Such a reaction was unexpected since these families are not closely related to one another.  Although inoculation of cut stem or branch sections may provide some indication of susceptibility or lack thereof, the ability of the fungus to attack an intact, living plant in the field is still a matter of question.

In addition to potential biocontrol agents from the native habitats of M. faya, other fungi are under investigation:

   A constant, usually low level of twig dieback, caused by Botyrosphaeria ribis, occurs through the M. faya population in Hawai‘i.  B. ribis has been reported in Hawai‘i on several woody hosts.

   Significant numbers of mature fruit of M. faya in Hawai‘i has been observed to become commonly infected with Botrytis cinerea, a pathogen already present in the environment (Duffy and Gardner, 1994).  This reduction in viable seed may, in effect, be a "spontaneous biocontrol" to which little previous attention has been given, but without which the invasive ability of M. faya would be even greater than it is at present.

    A species of the leaf-spotting fungus Septoria, at present referred to S. myricae, is becoming a problem in commercial plant nurseries in the southeastern U. S. where waxmyrtle ( Myrica cerifera) is grown for use in landscaping.  The fungus becomes a problem mainly under condtions of sprinkler irrigation.  Leaves with several leaf spots typically fall from the plant.  The fungus was tested on M. faya and found to be capable of attacking this species as well.  It is currently under consideration in Hawai‘i as a biocontrol agent.   Host range testing on plants from more than 20 families has indicated that the fungus is limited to the genus Myrica.  Under permit, the fungus has been released to the field, where inoculation trials are underway.

    Microscopic characteristics of Septoria myricae:  a pycnidial conidioma (left), and conidia (right).

         Inoculum of S. myricae is prepared in a kaolin formulation for storage.  It is applied by suspension in an aqueous sucrose solution, and applied to foliage of M. faya in the field with a commercial back pack power sprayer.

In recent years, an apparent spontaneous die-off of M. faya has been observed in Hawai‘i Volcanoes National Park.  The condition was typically fast-acting, quickly killing previously vigorous trees.  Whereas M. faya appeared most susceptible to the die-off, it became obvious that other plant species, including the endemic ‘ohi‘a, were attacked as well.  Several possible explantations for the condition were investigated, eventually leading to the feeding activity of the two-spotted leafhopper (Sophonia rufofascia), first reported in Hawai‘i in 1988.  The insect is thought to have originated in China.  Thus far, it has demonstrated an exceptionally wide host range in Hawai‘i, attacking a large number of unrelated crops, ornamentals, and native species.  The damage to its hosts is thought to be caused by a potent feeding toxin that is injected during feeding, rather than by a transmitted pathogen, such as a phytoplasma, as had been earlier postulated.

      M. faya trees killed by the two-spotted leafhopped in Hawai‘i Volcanoes National Park.