http://www.extento.hawaii.edu/kbase/crop/Type/f_prolif.htm
Various parts of orchid plants are attacked by this fungus. The most serious
disease caused by F. proliferatum on orchids is damping-off and rots of
young plants. Hundreds of young seedlings are lost in community pots due to
this devastating disease. Rots of these plants kill many and stunt the
growth of survivors. As surviving plants mature they are plagued by the
recurrence of fusarial diseases during wet periods.
On dendrobium plants at least 9 months old, new shoots are blackened by
Fusarium infections and slow rots develop especially at the leaf tip. Leaves
are lost and the entire apical tip of new shoots are commonly killed.
Fusarium proliferatum causes small (2 - 5 mm) circular to oval spots with
irregular edges. Spots expand very slowly. As the leaf matures, some of the
spots develop a black edge, while the center of the spots becomes sunken.
The leaf tissue surrounding the spot is slightly chlorotic or pale green.
With mature dendrobium plants, only the young leaves or wounded leaves are
susceptible, while mature unwounded leaves are resistant. The occurrence of
leaf spots on mature leaves is the result of infection when leaves were
young. The distribution pattern of leaf spots reflect the leaf position of
the unopened, young leaves of a new shoot. A characteristic pattern of spots
for this disease is a row of spots across the width of the leaf (Fig. 1).
Sunken brown spots also occur.
The fungus infects the leaf sheath causing black to dark brown rots with
irregular edges. Rots expand very slowly and after a few months, the center
of sheath blights or rots can be white to tan.
Circular to elongate spots also develop on flowers. Spots are tan to deep
brown with a dark border (Fig. 2).
On cattleya hybrids, elongated black rots on new leaves or blackened sheaths
of young shoots are caused by Fusarium proliferatum.
