Monday, October 5, 2009

Disease of the month: Dieback of Eugenia

Eugenia dieback symptoms
October's disease of the month is dieback of Eugenia, caused by the fungus Neofusicoccum parvum. Eugenia (scientific name=Syzigium paniculatum) is a popular ornamental that is often used in topiaries. It is a tree that is native to the rainforest, and is grown in the US in zones 10 and 11. Nurseries in Miami-Dade County produce an estimated 600,000 eugenia plants per year.

After Hurricane Wilma in November 2005, a serious dieback disease of eugenia first appeared in South Florida. Affected nursery plants had wilted, defoliated branches, with the dieback symptoms affecting anywhere from a few affected branches to the entire plant canopy. When diseased branches were cut longitudinally, the vascular tissue had a red discoloration (right).

Causal agent
N. parvum in cultureWork by Aaron Palmateer and Randy Ploetz has determined that a fungus, Neofusicuccum parvum, causes the dieback. Neofusicoccum parvum (=Fusicoccum parvum, teleomorph Botryosphaeria parva) is actually a complex of closely related species that have a wide host range, with 43 different hosts reported in the USDA-ARS Systematic Mycology and Microbiology Fungal Database. It also causes a dieback on Syzigium cordatum in South Africa, a native ornamental tree in that country. Neofusicoccum parvum has been associated with dieback on many other tropical and subtropical hosts, including avocado, guava, citrus, eucalyptus, and mango. The fungus grows rapidly in culture, producing fluffy grey colonies that darken with age. It can produce unicellular conidia that form septa and become pigmented with age, but many isolates grow vegetatively without producing spores.

Disease Cycle and Epidemiology
Dieback occurs mainly in the late summer, with the onset of high temperatures. The severity of external and internal symptoms increase as temperature increases. Sunlight does not impact disease severity, so the production of eugenia in full sun is not a contributing factor to the disease.

water stress/fertility experimentFurther research is needed to fully characterize the disease cycle and to determine the environmental factors that contribute to disease development. We have a greenhouse experiment underway (right) to evaluate the role of water stress and soil fertility in causing dieback symptoms. In the future we plan to investigate how the pathogen is spread from plant to plant.

Currently it is recommended to use good sanitation measures to manage this disease. This includes pruning symptomatic branches and removing the diseased cuttings from the nursery. Sanitize all tools used to prune or work with plants before each use. It's best to sanitize pruning shears between each plant. Some growers handle this by dipping shears in bleach and then dunking in oil after drying (to minimize rust). Examples of disinfectants for tools include: 1) 25% chlorine bleach (3 parts water and 1 part bleach; 2) 25% pine oil cleaner (3 parts water and 1 part pine oil); 3) 50% rubbing alcohol (70% isopropyl; equal parts alcohol and water); 4) 50% denatured ethanol (95%; equal parts alcohol and water); 5) 5% quaternary ammonium salts. Soak tools for 10 minutes and rinse in clean water. Do not mix quaternary ammonia with bleach.

Chemical control options include applying a copper based fungicide according to the manufacturer's label. Recommendations include applying fungicides after pruning to minimize infection of the freshly cut tissue. Be certain to achieve good coverage especially on new wounds made during pruning. Because it is likely that plant stress contributes to disease outbreaks, the maintenance of plant health is likely important for dieback management. Although information on this new disease is relatively limited, an extension publication is in preparation, and the following publications give more information on the pathogen and disease:

VIDEO: Check out our video from a trip to a topiary nursery on the west coast of Florida.

Thursday, October 1, 2009

Welcome to the Plant Diagnostic Clinic.

We'd like to use our first blog post to familiarize our followers with the TREC Plant Diagnostic Clinic, located at the University of Florida Tropical Research and Education Center in Homestead, FL. Our clinic is responsible for the diagnosis of diseased plant samples submitted from southern Florida. We get an average of 16 samples every week, 95% of which are diseases or insect problems from ornamental plants. This year we have already diagnosed 619 samples!

So who can use the services we provide? Anyone can. While most of our clients are commercial growers and nurseries, we also help homeowners, extension agents, and researchers.

The clinic is run by Dr. Aaron Palmateer, who is supported by several staff members: Ian Maguire, Tara Tarnowski, and Jill Ploetz. Also, several TREC faculty are affiliated with the diagnostic clinic. Diseases of vegetables are diagnosed by Dr. Shouan Zhang. Ornamental plant samples affected by insect pests are diagnosed by Dr. Catherine Mannion. Insect samples from vegetable crops are diagnosed by Dr. Dak Seal and Dr. Jorge Peña diagnoses insect pests associate with tropical fruits.

In addition to diagnostics, we have an ornamental pathology research program. Right now we have several projects in the works, including investigating environmental factors influencing Eugenia dieback caused by Neofusicoccum parvum, chemical trials to identify products to manage an array of diseases, and developing rapid and easy diagnostic tests using molecular tools.

In this blog we will keep you updated on new developments in the clinic, as well provide posts on our "Disease of the Month".