Winter 2012 - Miami-Dade County Extension Office - University of ...
Winter 2012 - Miami-Dade County Extension Office - University of ...
Winter 2012 - Miami-Dade County Extension Office - University of ...
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Update from the Florida <strong>Extension</strong> Plant Diagnostic Clinic<br />
By Aaron Palmateer & Stephanie Suarez, UF-IFAS Tropical Research & Education Center<br />
This has been a really busy year for the Florida<br />
<strong>Extension</strong> Plant Diagnostic Clinic at the Tropical<br />
Research & Education Center in Homestead. Hot<br />
temperature, high humidity, and record-<br />
breaking rainfall created highly favorable<br />
conditions for a variety <strong>of</strong> plant diseases. Leaf<br />
spots, mildews, wilts, and anthracnose are just<br />
some <strong>of</strong> the most common and aggressive<br />
diseases attacking tropical foliage plants.<br />
Leaf spots caused by<br />
Xanthomonas and<br />
Pseudomonas were found on<br />
a number <strong>of</strong> tropical foliage<br />
plants, but sample numbers<br />
were greatest for Ficus (F.<br />
microcarpa ‘Green Island<br />
Ficus’, F. elastica aka rubber<br />
tree, F. benjamina and F.<br />
lyrata ), Duranta erecta<br />
(Golden Dew Drop or Gold Mound), and<br />
Poinsettia. Bacterial pathogens typically cause<br />
water-soaked spots on leaves that are confined<br />
between the leaf veins and sometimes appear<br />
angular in shape with a yellow halo. Bacterial<br />
plant diseases are <strong>of</strong>ten the most difficult to<br />
control and require quick detection and<br />
preventative action to manage.<br />
Mid to late summer we experienced a dramatic<br />
influx <strong>of</strong> plant samples submitted to the<br />
diagnostic clinic that were diagnosed with<br />
southern wilt caused by the<br />
bacterium Ralstonia<br />
solanacearum. There are<br />
different strains <strong>of</strong> this<br />
bacterial pathogen called<br />
biovars and we’re finding<br />
two that cause disease on<br />
Mandevilla and Pothos. This<br />
disease affects the vascular<br />
tissue where symptoms<br />
include root rot, yellowing<br />
and browning <strong>of</strong> the leaves, and wilt that ultimately<br />
leads to plant death. If you happen to see these<br />
symptoms on Mandevilla or Pothos, it is<br />
recommended that you remove and discard the<br />
plants so that the disease does not spread.<br />
Fungal plant pathogens are the most common and<br />
South Florida has a lot <strong>of</strong> them.<br />
This year brought more plant disease samples than<br />
ever before. Root and stem rots, leaf spots,<br />
hardwood rots and wilts were just some <strong>of</strong> the plant<br />
diseases caused by fungi this year. One disease<br />
that’s been receiving a lot <strong>of</strong> publicity in South<br />
Florida, laurel wilt <strong>of</strong> avocado, has been keeping the<br />
clinic busy. We continue to receive avocado trunk<br />
tissue samples to be tested for laurel wilt. For<br />
instructions on how to properly take samples and<br />
more information about the disease refer to the<br />
following website: http://www.savetheguac.com.<br />
One leaf spot pathogen that<br />
causes disease on palm trees is<br />
Calonectria. This pathogen<br />
infects several species <strong>of</strong> palms<br />
and is mostly a problem in<br />
production nurseries. The<br />
diagnostic clinic has received<br />
several samples <strong>of</strong> Calonectria<br />
leaf spot over the past few<br />
months on Chamaedorea<br />
cataractarum (cat palm), Ravenea<br />
rivularis (majesty Palm), and Howea forsteriana<br />
(kentia palm).<br />
Colletotrichum is another fungal plant pathogen<br />
and the disease it causes is referred to as<br />
anthracnose. This pathogen has a very broad plant<br />
host range and can be seen in everyday landscapes<br />
but is very common on such plants as Orchids,<br />
Sansevieria, woody ornamentals and palm trees.<br />
Some people may be more familiar with the disease<br />
(Continued on page 7)<br />
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