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Stubborn Disease
Spiroplasma citri

Stubborn Disease, Spiroplasma citriThe sources from which I first diagnosed the problem with my tangelo tree to be stubborn disease listed the cause as a virus.  Recently I found that the cause has been identified as a bacterium.  Spiroplasma citri belongs to a group of the smallest bacteria, so small that it is "almost" a virus.  The first sign of trouble was the curling of new leaves.

Stubborn Disease, Spiroplasma citriSoon after the new leaves curl, they die and drop off, leaving bare branches sticking out where new growth should be.  As a result the foliage became very sparse, consisting only of older leaves.  Another symptom is that the fruit tend to be lopsided.

Stubborn Disease, Spiroplasma citriThe next season the tree appears to be recovering.  But the new growth is very bushy, since the normal growing tips are dead, and new branches come out from farther back.  Stubborn disease is spread by bugs called leafhoppers (leafhopper 1, leafhopper 2).

[ Classification, Taxonomy ]

[Monera ]  [Backyard Biology ]  [ Science Can Be Fun ]