 |
 |
Greasy Spot (fungus - Mycosphaerella citri)
.
This
is a very common disease in Texas. The fungus is primarily a leaf pathogen,
but it can also infect fruit. Yellow spots are seen at first on the upper
surface of the leaf [Picture]. The corresponding
areas on the undersides of the leaves turn dark and appear slightly raised
and greasy [Picture]. With severe infection,
leaves may turn yellow and drop prematurely. The infection is favored by rust
mite injury and humid weather. Yellowing caused by scale insects may be mistaken
for early symptoms of greasy spot [Picture].
Either citrus oils or fungicides can be applied during the summer for control. Heavy infections occurring in wet years may require 2 to 3 fungicide treatments. Since infection occurs on the lower leaf surface, thorough spray coverage is essential for effective control. The spores of the fungus originate in the leaf litter on the orchard floor and are released following rainfall or irrigation. Thus, removing litter will reduce the amount of spores present.