Citrus canker control: tips on treating citrus canker disease

Citrus canker is a financially devastating disease that has
been eradicated from the citrus market a couple of times only to return again.
During past eradication attempts, thousands of trees were destroyed. Today,
mass eradication has been deemed unfeasible, but there is still a quarantine
regarding shipping or taking citrus across state lines. So, what exactly is
citrus canker? Read on to learn about citrus canker symptoms and how to treat
the disease should it appear in the home garden.

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What is Citrus Canker?

Citrus canker goes way back to its discovery in Texas in
1910 and into Florida in 1914. It was introduced on seedlings imported from
Japan. It is caused by the bacterium Xanthomonas
citri and likely originated in southern Asia. The disease can now be found
in Japan, the Middle East, central and southern Africa, and Central and South

This bacterium is extremely contagious and is fostered when
there is steady rain combined with high temperatures. Both rainwater and
overhead irrigation spread the bacteria from plant to plant and is then further
spread by wind, birds and animals, people and machinery.

Asian leaf miners also play a part in the spread of citrus
canker. They do not act as vectors but rather cultivate infection and spread of
the disease through damage caused in the foliage via feeding.

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Citrus Canker Symptoms

The initial symptoms of citrus canker are raised lesions
that can be found on both sides of the leaf. They have a crater-like appearance
surrounded by concentric circles. They may have a water-soaked margin and a
corky texture. As the disease progresses, the lesions may be surrounded by a
yellow halo.

Further into the infection, these halos become shot holes.
You may see fungi (white fuzz) and fruiting bodies (black dots) on older
lesions as well. The exact look of the disease varies depending upon the citrus
tree variety and the length of time the tree has been infected.

How to Treat Citrus

During initial infections in the United States, the only
method available for treating citrus canker was to burn infected trees, an
effort first waged by growers and then taken over by the agricultural state
departments. Rigorous citrus canker controls were instigated wherein infected
trees were not only destroyed, but all green wood trees were removed within a 50-foot
radius of those infected. The disease was finally declared eradicated in 1933
at a cost of $6.5 million!

Today, with regards to treating citrus canker via chemicals,
worldwide the disease is managed with preventive copper-based bactericides.
This is generally used in conjunction with cultural practices such as pruning
and defoliation of diseased summer and fall shoots and the use of windbreaks.
Pruning is also done in the dry season when conditions are less favorable for
the spread of the bacteria.

Other citrus canker control methods include the use of
resistant citrus varieties and the introduction of a USDA quarantine program
with restrictions on taking and bringing fruit into various states. Eradication
has been deemed unfeasible due to a number of factors, primarily the cost and
general uproar by non-commercial growers.

Bild von eyen120819
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