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New Findings on Limb<br />
Dieback of Figs in California<br />
Pruning Practices Can Help Protect<br />
from Disease Pathogen<br />
By THEMIS J. MICHAILIDES | Plant Pathologist, UC Davis/Kearney Agricultural Research and Extension Center<br />
DAVID MORGAN | Staff Research Associate, UC Kearney Agricultural Research and Extension Center<br />
and GIORGIO GUSELLA | Graduate Student in Plant Pathology, University of Catania, Italy<br />
Back in 2004, and again in recent<br />
years, there were concerns by fig<br />
growers mainly in Madera and<br />
Merced counties about an excessive<br />
killing of major branches of their fig<br />
trees (Figure 1). Visits to some orchards<br />
back then and recently indicated<br />
that indeed they had a major problem.<br />
Initial close examinations of the dead<br />
branches showed symptoms which<br />
were similar to another disease: branch<br />
wilt of walnut.<br />
The bark of dead fig branches had<br />
cracks and one could easily remove<br />
large pieces of the bark, exposing the<br />
woody tissues underneath which were<br />
covered by a black powder. Rubbing<br />
this black powder with your finger<br />
could easily remove masses of it (Figure<br />
2, see page 25). The inner surface<br />
of the broken and removed bark pieces<br />
were also black due to these powder<br />
masses. A lot of trees had many dead<br />
major branches while others had one<br />
or two dead along with other branches<br />
bearing chlorotic and thin canopy, distinct<br />
from the green and dense canopy<br />
of healthy branches.<br />
Figure 1. Left, Fig tree affected by severe limb dieback; top right, still active canker; bottom<br />
right, inactive canker (branch is dead) (all photos courtesy G. Gusella.)<br />
Pathogen Activity<br />
To collect samples, we cut some of the<br />
symptomatic branches close to the<br />
interface of dead and alive-looking<br />
(green) tissues. We noticed that in a<br />
cross section, the dead woody tissues<br />
were delineated from the healthy tissues<br />
by a dark brown line while the living<br />
woody tissues were white (Figure 1).<br />
Slices of these woody tissues from the<br />
branches were taken, isolations were<br />
made in the laboratory and a fungus<br />
known to be a pathogen of woody<br />
tissues was consistently recovered.<br />
The name of this pathogen is Neoscytalidium<br />
dimidiatum, which is a new<br />
taxonomic name of Hendersonula<br />
toruloidea fungus, which represents<br />
the pathogen first reported to cause the<br />
24 Progressive Crop Consultant March / April 2021
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