Tuesday, December 1, 2009

Clinic Update 12/01/09



We had a pretty eventful past couple of weeks. Dr. Palmateer and Tara Tarnowski traveled to Puerto Rico to meet with Dr. Consuelo Estevez de Jensen , director of the University of Puerto Rico Plant Diagnostic Clinic, which is located in Juana Diaz. We are currently collaborating on a project to investigate more sensitive PCR methods for molecular diagnostics. We spent a day at the experiment station in Juana Diaz, trying out a new PCR method. We also travelled to Mayaguez to visit the Plant Pathology department at the Mayaguez Department, and visited with Dr. Brian Irish at the USDA-ARS station. He showed us their extensive collection of cacao germplasm, as well as many other neat tropical plants they have at the station. See photos to the left of the University of Puerto Rico experiment station in Juana Diaz, Dr. Estevez de Jensen in the USDA cacao collection, the biggest baobob tree on the island (also at the USDA station), and Dr. Palmateer appreciating one of the many breathtaking views on the island.


On October 13th, a group of agricultural scientists from Germany visited TREC. We showed them around the clinic and our tropical fruit collections. They then toured several local nurseries. The whole group seemed to enjoy seeing all the tropical fruit and foliage crops we have here in south Florida.

Finally, on October 20th, the latest group of Master Gardeners from right here in Miami-Dade county came through for a tour. The were enthusiastic about everything we showed them, and asked all sorts of questions. We had fun looking at several disease samples together and testing their diagnostic skills. All of them did a pretty good job of distinguishing between symptoms and signs, and were really excited to see vascular discoloration, bacterial streaming, and several photos of fungal spores taken from the samples we were looking at. What a fun group!

Friday, November 13, 2009

Disease of the Month: Physiological disorders of tropical foliage plants

Physiological disorders of tropical foliage plants

This month we are taking a look at two physiological disorders commonly seen on foliage plants here in south Florida during the colder months. Physiological disorders are not caused by pathogens, but by environmental factors instead. Because these disorders are not caused by biotic agents, they are not infectious and will not spread.

Oedema (edema) occurs when roots take up water faster than it can be used by the plant or transpired through the leaves. Water pressure builds up in the mesophyll or internal cells of the leaf causing them to enlarge and form tiny swollen blister like areas. The swollen blisters are usually round, and can become corky with age. The tissue under the surface of the lesion, however, often remains green. Oedema lesions can resemble insect galls or scale insects, but scales can be scraped off of the plant surface while oedema blisters cannot.

See above for a photo of oedema on orchid, and below for oedema on sapodilla (front and back of leaf).

Oedema is most common during winter months in south Florida (November-March) especially during extended periods of cooler, cloudy weather. The cooler air temperature slows transpiration and water evaporation by the leaves, and so excess water in the warmer soil is absorbed by the roots faster than it is lost from the leaves. Several tropical plant species are very susceptible to oedema. For example, Ixora, Peperomia, and some orchids may show symptoms of oedema any time throughout the year due to favorable conditions (i.e. excessive water, low air movement, etc.).

Oedema lesions are permanent, but under favorable growing conditions, affected plants will produce healthy new growth. Although it may be tempting to remove affected leaves as soon as lesions appear, these leaves are still able to photosynthesize and so removing them may be harmful to the overall health of the plant. Once sufficient new growth is present, the older blistered leaves can be pruned out. The most important step in preventing oedema is to make sure plants are not over watered, especially during cooler weather. Water in the morning, as daily temperatures are rising. Spacing plants further apart to allow more air flow on leaf surfaces can also reduce oedema. For potted plants, avoid accumulation of water in saucers and use well-drained soil mix.

Mesophyll cell collapse is another physiological disorder that occurs after exposure to low water or air temperatures. The low temperature directly damages the mesophyll cells of the host, but symptoms may not appear for 6-8 weeks after damage occurs. Symptoms are localized or large areas of sunken or yellow spots on the foliage. These areas may become brown and necrotic with age, and saprotrophic (not pathogens) fungi may colonize the dead tissue. New leaves are more susceptible than older leaves. On orchid species, temperature of 35-45°F and water that differs by more than 25°F from leaf tissue can cause mesophyll cell collapse. Some studies also suggest that extreme fluctuations in day/night temperatures may lead to the condition.

Mesophyll cell collapse can be difficult to diagnose because symptoms develop many weeks after the damage occurs. If you suspect that the symptoms you are seeing are due to mesophyll cell collapse, you can check temperature records for the area or greenhouse for the last six weeks and look for cold temperatures or extreme fluctuations in high/low daily temperatures. Also, the pattern of symptoms seen can be clue as to whether the damage is due to mesophyll cell collapse. If the damage is due to a single cold temperature event, symptoms will be seen on a few newer leaves, but growth developing after symptom development should be healthy.

Like oedema, damage from mesophyll cell collapse is permanent, but several steps may be taken to prevent or minimize future damage. When watering plants, take care that water is not too cold (more than 25°F/4°C different than plant tissue). Sensitive plants may need extra protection from cold temperatures (heaters and physical protection from cold winds).

Several IFAS extension publications exist for these two physiological disorders as well as other disorders caused by environmental factors:

Publication #PP265 Physiological Disorders of Orchids: Mesophyll Cell Collapse. R.A. Cating and A.J. Palmateer.

Publication #PP244 Physiological Disorders of Orchids: Oedema. R.A. Cating, A.J. Palmateer, C.M. Stiles, P.F. Harmon and D.A. Davison.

Publication #PP248 Guidelines to Idenitification and Management of Plant Disease Problems: Part 1. Eliminating Insect Damage and Abiotic Disorders. Monica Elliott, Ken Pernezny, Aaron Palmateer, Nikol Havranek.

Also, here is a thorough treatment of abiotic diseases on houseplants from the American Phytopathological Society:

APSnet Feature: Non-infectious diseases of common houseplants. January 2001.

Monday, November 2, 2009

BLOG POST 11/02/09

We've been busy this last couple of weeks, with 24 samples to diagnose and experiments underway. On October 16, we had a group of students in a tropical cropping systems class from Gainesville come down to TREC for a visit, and we talked about the ornamental industry here in Florida, as well as the function of the diagnostic clinic. It is always astonishing to read the statistics about how large the nursery industry is--it has an economic impact of $2 billion dollars a year, and provides about 40,000 jobs!

Dr. Palmateer gave a plant pathology training at the Miami Dade County Extension for the Master Gardeners. He was impressed at how interested and engaged the audience was.

Our newest dieback of Eugenia project is underway, we are testing different fertility and irrigation rates to see how they influence disease development. We currently have seventy healthy plants in our greenhouse, which we plan to inoculate next week, and then monitor for disease development. Our hope is that this experiment will provide useful information for growers about how to manage the disease with cultural methods.

Have a look at the Clinic website if you haven't already. You can find helpful information about the proper way to submit a sample (including a video demonstration), as well as contact information for Clinic staff.

Vegetable season is starting, so we expect to see more vegetable samples coming in...

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".