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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 />

6

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