Ornamental crop production is the most important section of agriculture in Miami-Dade County, contributing nearly $1 billion in 2022. Because of the aesthetic values of the ornamental plants, various diseases are a limiting factor to the profitability of local growers. The diagnostic service of the plant clinic at the University of Florida Tropical Research and Education Center helps growers decide how to proceed when their plants look abnormal.
When mailing plant samples to the plant clinic, a sample submission guide prepared by Peres et al. (https://edis.ifas.ufl.edu/publication/SR007) is a good reference to follow. In Miami-Dade County, however, most ornamental growers can deliver their plant samples to the plant clinic. Unfortunately, neither a pathogen nor a pest was found in some of the plant samples submitted, many times due to the quality of the samples.
The publication by Peres et al. provides general guidelines for submitting disease samples of good quality to identify the pathogen leading to the damage, including aboveground part and root infections. Since the purpose of submitting plant samples is to determine the way to properly treat the plants, samples that may lead to inaccurate diagnosis, including totally necrotic, dry, and long-dead, as shown in this example (Fig. 1), are not good samples to be submitted. The plant sample in Fig. 2 is still okay for submission; however, it is too late to save the plants like that, even with an accurate diagnosis. The best samples to submit are those exhibiting early symptom development. This is particularly relevant for plants that have foliar diseases, as shown in Fig. 3. When you see wilting, chlorosis, dieback, and decline of the aboveground parts, such symptoms often indicate there might be a problem with roots (Fig. 4). Growers should bring the whole plant, including soil, to the plant clinic for a diagnosis. In addition, inadequate sample quantity and quality could also affect the accurate diagnosis, as shown in Fig. 5. Bring in at least 12 leaves with typical symptoms or problems to the clinic for potential tests (Peres et al.). Except for specific purposes, do not submit leaf samples that look healthy, as shown in Fig. 6 A and B. Instead, you can bring a few leaves to the plant clinic or extension office for a quick consultation before you pay for a formal diagnosis.
In addition, soil was submitted together for some plant samples, and low EC values were seen in some of the reports, indicating that poor nutrient status may lead to the problem. When plants grow under stress, such as abnormal pH and nutrient levels, most of the plants will show similar symptoms. This is different from the disease incidence pattern, which usually is clustered. If the majority of the plants are affected, growers may test their soil pH and EC level first, if they have the equipment, before submitting a sample.
Whenever local growers have an issue with their plants, your local extension agent is always here to provide help. Even though the agent may sometimes not be able to tell what has caused the problem, the agent can help you with the best option or prepare the best sample for the following tests. Such service is free of charge and a phone call away.
(Pictures were plant samples submitted to the Plant Clinic at UF TREC)
Fig. 1 A and B
Fig. 2
Fig. 3 
Fig. 4
Fig. 5
Fig. 6 A and B
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