South American Leaf Blight:
essential data |
Disease Name, Other
Names, Crops Affected Causative
Agent, Synonyms,
Description
of the Agent Symptoms Prevention
and Treatment
Other Comments |
| Disease name |
South American leaf blight |
| Other Names |
none |
Causative Agent
|
Microcyclus ulei |
| Synonyms |
- Aphosphaeria ulei,
- Dothidella ulei,
- Fusicladium ulei
|
| Crops Affected |
Rubber plants of the genus Hevea.Not all species
of the genus are affected and the disease is currently confined to
tropical Latin America and the Carribean. |
| Description of the Agent |
M. ulei is an ascomycete, a member of the sac fungi. One
of the features of these fungi is that they generate spores, called
conidia or conidiospores, that can be easily dispersed by the wind
and splashing rain drops and do not need insects or other animals
to spread them, although they may also play a role.
The fungus produces two other types of spore. The pycnidiospore
does not play a significant role in spreading the disease. The ascospores
are the product of the sexual cycle of the fungus and they are spread
at night, whereas the conidia are spread during the day.
|
| Symptoms |
The disease is only seen on young leaves of the plant (less than
10-15 days old) and can be a risk to mature plants that have begun
to shed leaves annually. The first sign are discolored green masses
on the leaves that become gray as the fungus starts to produce conidia.
These spots can grow together, consuming the leaf causing it to die
and fall.
Older leaves are less susceptible to the disease and when they
are infected the fungus produces dense bodies called pycnidia that
may fall away and tear a hole in the leaf making it susceptible
to further damage or infection. |
| Prevention and Treatment |
The fungus can be controlled by a number of fungicides,
including:
- benomyl
- carbendazim
- chlorothalonil
- fenarimol
- mancozeb
- propiconazole
- thiophanate methyl
- triadimenol
- triadimephon
- triforin.
Benomyl-resistant strains have been found in Brazil.
Some species are not susceptible to the disease, and some strains
of susceptible species are resistant and crown budding or grafting
of resistant plants onto productive trees can be used to control
spread.
The fungus is quite sensitive to local conditions for germination
and careful selection of sites can be used to create safe havens
called escapes where at least part of the crop can be protected.
|
| Other Comments |
The disease currently threatens the fairly small
(<1% of total rubber production) western hemisphere rubber crops
and quarantine is the primary method of keeping it out of Asian
rubber plantations.
Rubber is arguably the most important non-food crop in the world
and a loss of rubber supplies could have a crippling effect on most
economies.
M. ulei is no respecter of reputation or money. When Henry
Ford tried to establish the ill-conceived Fordlandia rubber plantations
in the Amazon Basin in the 1920's South American Leaf Blight devastated
the seedlings. The plan was not helped by attempting to apply North
American farming methods to the complex ecosystems of the Amazon.
|