Sampling for Laurel Wilt

Jonathan H. Crane, Tropical Fruit Crop Specialist 

May 23, 2012  (Download PDF - Click Here)

Sampling declining trees 

1. Equipment: pruning hand saw or hatchet, plastic zip-lock bags, permanent marker, gloves, disinfectant (Pine-Sol, 1 oz in 8 oz water), flagging tape and latex paint. 

2. Information on the plastic sampling bag: 

a. Date 

b. Your name 

c. Name of grove 

d. Location of the tree (row, tree number) 

e. Cultivar (variety) of avocado. 

f. Write the words “Laurel Wilt sample” 

3. Take a sapwood sample. The sapwood is the first 2-4 inches of wood just under the bark. Healthy sapwood is white to off-white in color. Unhealthy sapwood has dark brown to bluish to black streaks in the sapwood. 

a. Where on the tree to sample? First look to see where the canopy is showing signs of decline and then look for evidence of beetle holes – try to sample in these areas. 

b. Sampling options 

• Sample by hatchet. The bark of avocado trees can be thick (1/2 to 1 inch or more). The outer bark is rough and greyish colored and the color of the inner bark is pink. Remove the outer and inner bark until you see either dark-stained (streaked) wood. Once sapwood is exposed take chips of the symptomatic (brown-streaked) sapwood and place in the bag for analysis. We need about . cup or so of this wood. 

• Sample by hand-saw. Removing the bark is not necessary. Cut a wedge-shaped (<) piece of wood such that the pointed end extends several inches into the sapwood. We need 1 to 2 pieces. 

c. Paint the wound made by the sampling with a thick coat of latex or oil-based paint to discourage additional beetle infestation. Spray paint will not inhibit beetle boring. 

d. Sanitize the hatchet or hand-saw after each sample to prevent the spread of the disease. Examples of disinfectants 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 (equal parts alcohol and water); 5) 5% quaternary ammonium salts. There are ammonium chloride based disinfectants (i.e. Green-Shield® or KleenGrow™) that are good disinfectants for cleaning tools. Do not mix quaternary ammonia products with bleach. 

e. Take the labeled sample or samples to the TREC Plant Diagnostic Clinic at 18905 S.W. 280 St., Homestead, FL 33031. Please fill-in the sample form sheet at the clinic. The charge is $40.00. 

f. The analysis should be completed within 10 business days of sample delivery. 

Disease Control & Plant Health Strategies in Ornamentals 
PDF - Click Here

Dr. Ann Chase 

Professor Emeritus of Plant Pathology 

University of Florida, MREC 

Dr. Aaron Palmateer 

Assistant Professor of Plant Pathology 

University of Florida, TREC 

Paul Pilon 

Perennial Solutions Consulting 

AGENDA: 

8:00–8:50 a.m. – Registration 

8:50–9:00 a.m. – Introduction (BASF) 

9:00–9:30 a.m. – What is Plant Health (BASF) 

9:30–10:20 a.m. – Plant Health: Trial Results and Significance to Greenhouse and Nursery Operations – Paul Pilon 

10:20-10:30 a.m. – Break 

10:30-11:30 a.m. – Ornamental Disease Management & Update – Dr. Ann Chase 

11:30-12:30 p.m. - Disease Management in Ornamental Nurseries – Dr. Aaron Palmateer 

12:30 p.m. – Lunch - sponsored by BASF 

4 REGIONAL SEMINARS OFFERED!!! 

June 26, 2012 at the UF/IFAS Miami-Dade County extension office, Homestead 

June 27, 2012 at the Palm Beach County UF/IFAS extension office, Palm Beach 

June 28, 2012 at the Gulf Coast Research and Education Center, Wimamua 

June 29, 2012 at the Mid Florida Research and Education Center, Apopka 

CLICK BELOW FOR FREE REGISTRATION 

Disease Control & Plant Health Seminar 

www.eminj.com/BASF/PageantIntrinsic/Registration.cfm 

Sponsored By:

Managing downy mildew of impatiens in the nursery and landscape

Dr. Aaron  Palmateer's
Managing downy mildew of impatiens in the nursery and landscape - PDF - CLICK HERE

Downy Mildew on Impatiens

Check out:

Downy Mildew on Impatiens FactSheet (Stay tuned for new management recommendations)

Click Here: http://palmbeachcountyextension.wordpress.com/2012/01/26/downy-mildew-on-impatiens/

University of Florida / IFAS Palm Beach County Cooperative Extension Service 

Laura Sanagorski, Environmental Horticulture Extension Agent  , Bill Schall, Commercial Horticulture Extension Agent 

Downy mildew of cucurbits: identification and management By Dr. Shouan Zhang UF/IFAS/TREC

Downy mildew is one of the most economically important diseases of cucurbits, especially in areas with high humidity and rainfall such as South Florida. This disease occurs on cucurbits including cantaloupe, cucumber, pumpkin, squash and watermelon. Downy mildew is an annual disease problem on pumpkin and squash in eastern and central US states for many years.  A tremendous breeding effort in the mid-twentieth century resulted in adequate control of this disease in cucumber production without fungicide application. However, downy mildew has become one of the most important diseases in cucumber since 2004.  The resurgence of the devastating disease has caused substantial economic losses to cucumber growers, and it continues to be an important disease problem in other cucurbit crops that significantly impacts the cucurbit production. Because the production of cucurbits exists year-round throughout the state of Florida, downy mildew is endemic and occurs nearly every growing season to some degree.

Fig. 1 Damage to cucumber plants by downy mildew in the field. 

Look out for the symptoms

Downy mildew begins as small water-soaked lesions on the underside of leaves. The lesions are usually limited by small leaf veins, giving the lesions an angular appearance. It is caused by an oomycetous pathogen called Pseudoperonospora cubensis. Under high humid conditions, a layer of gray-brown to purplish-black fluffy stuff appears on the underside of the infected leaves.  Inspection with a microscope of the presence of the acutely and dichotomously branched sporangiophores (tree-liked structure) bearing lemon-shaped sporangia is characteristic of the downy mildew pathogen. Leaves will turn necrotic and curl upwards within days if the weather condition favors the pathogen. Therefore, scouting for the disease is critical. 


Symptoms of downy mildew vary on watermelon and cantaloupe, and the lesions are not always angular and often associated with an upward curling of the leaves. The pathogen of downy mildew does not affect fruits of cucurbit crops. However, it can result in significantly reduced yields and deformation of fruits especially in cucumber.  In addition, increased exposure to direct sunlight due to early defoliation causes more sun-scalded fruits in watermelon and winter squash.

Fig. 2.  Symptoms of downy mildew on upside (left) and underside (right) of cucumber leaves. Note the angular and chlorotic lesions on infected leaves.  

(http: www.cals.ncsu.edu/plantpath/extension/fact_sheets/Cucurbits_-_Downy_Mildew.htm)

The mystery behind downy mildew

Pseudoperonospora cubensis is an obligate parasite that requires live host tissues in order to survive and reproduce. The pathogen must overwinter in an area that has mild weather in winter season, e.g. South Florida, and where cucurbits are present.  The spores are dispersed via wind or splash water to neighboring plants and to other fields by wind or irrigation water.  Symptoms appear several days to nearly two weeks after infection.  


The pathogen favors cool and moist weather.  Therefore, downy mildew is common during winter growing seasons in South Florida. Optimum conditions for sporulation are 15-25°C (59-77°F) with 6 to 12 hours of water film on the leaves such as morning dew. Sometimes temperatures during daytime are not favorable for this pathogen, however, nighttime temperatures may be ideal.

Fig. 3.  Symptoms of downy mildew on upside (left) and underside (right)

of butternut squash leaves. Note the gray-brown to purplish-black ‘down’ on the underside of the infected leaves.

Fig. 4.  Symptoms of downy mildew on leaves of cantaloupe (left) and watermelon (right). Note irregular lesions and turn brown to black in color.

(http: www.cals.ncsu.edu/plantpath/extension/fact_sheets/Cucurbits_-_Downy_Mildew.htm)

Downy mildew management

Resistant Cultivars

Host resistance is most economically important and effective component in integrated disease management and should be utilized whenever possible. Resistant cultivars have been developed for cucumbers and cantaloupe, and to a lesser extent for squash and pumpkin.  Though downy mildew has been severe on resistant cucumber cultivars in recent years, they are more effective than susceptible cultivars in delaying infection.

Early Detection

Early detection of downy mildew is critical for preventing cucurbits from the damage of this disease due to its rapid and destructive nature. Many growers lost huge values of cucurbits to downy mildew as they waited until symptoms of the disease were clearly seen before initiating sprays. Following early detection, immediately applying preventative fungicides is imperative for the control of this destructive foliar disease. A downy mildew forecasting system (http://cdm.ipmpipe.org/) has been established to assist cucurbit growers in timing their fungicide applications for maximum benefit.  The system documents the disease outbreaks and provides a risk assessment for future outbreaks in regions where cucurbits are grown.

Chemical Control

It is unlikely to achieve satisfactory control of downy mildew without the use of fungicides. Many growers heavily rely on fungicides for downy mildew control due to the aggressive and destructive nature of this disease. Both protectant and systemic products should be applied. Fungicides are effective in downy mildew control when applied prior to infection and continually sprayed at 5- to 7-day intervals. Previcur Flex, Tanos, Ranman, Reason, Presidio, Aliette and Quadris are examples of fungicides for control of downy mildew in Florida.  The products should be applied in a program to prevent resistance development in the pathogen population by rotating with fungicides of a different mode of action. Protective fungicides such as chlorothalonil and mancozeb should be incorporated as mixing partners. All fungicides should be applied according to the manufacturer's label. 

Shouan Zhang is a vegetable plant pathologist based at the IFAS Tropical Research

and Education Center, University of Florida in Homestead, FL. 

He can be reached at:

EMAIL: szhang0007@ufl.edu

PH: (305)246-7001 ext. 213.

Bacterial blight of Ficus Caused by Xanthomonas

Species of Ficus are common tropical foliage plants used for interior decoration and in landscapes throughout warm climates such as South Florida. Ficus species used as foliage plants include F. altissima, F. benjamina, F. binnedijkii, F. elastica, F. lyrata, F. microcarpa, F. pumila, F. retusa, and F. rubiginosa among others . Florida has led the nation in the production of foliage plants, accounting for more than 55% of the national wholesale value since the 1960s (Chen, J., R.J. Henny, and D.B. McConnell. 2002)

Hot, humid, and rainy conditions (typical summer in South FL) are highly favorable conditions for plant disease. Xanthomonas is a bacterial plant pathogen that thrives under these conditions and is spread very effectively in water, especially windblown rain. Once cells of the bacterium come into contact with the plant they enter through wounds or natural openings such as stomata or hydathodes. Once inside the plant they can move systemically causing a severe blight of the leaves.

Xanthomonas campestris pathovar fici is reported to be the causal agent of bacterial blight affecting species of Ficus. Host studies indicate that several Ficus species and cultivars are susceptible including F. benjamina , F. buxifolia, F. triangularis, F. mexicana, F. maclellandii ‘Alli’, F. retusa ‘California Nitida” and ‘Green Gem’ and F. Grennisland (Chase and Henley 1993)

Symptoms:

On young plants initial symptoms appear as small, water soaked, circular lesions with irregular borders near the leaf margin (Fig 1)

After 7 to 14 days of initial infection, lesions enlarge, coalesce and typically cover large portions of the leaf area (Fig 2)

Premature senescence and leaf drop is common. When young plants (liner stage) become infected the disease can be fatal (Fig 3)

Older plants can also become infected and show a range of symptoms. Spots on the upper surface of leaves are brownish-black with a chlorotic halo (Fig 4) and leaf tissue appears water soaked on the opposite side (Fig 5)

Management:

Be certain to monitor irrigation and avoid watering late in the day or evenings. If using overhead irrigation water in the morning, so that the foliage has time to dry before evening. Allowing the foliage to dry will reduce spread of the bacteria. Using micro jet or drip irrigation minimizes moisture on the foliage and reduces Be sure to surface disinfest all pruning tools. Good sanitation is crucial for managing bacterial pathogens.

As a preventative measure apply one of the following labeled pesticides according to the manufacturer. If copper based fungicides have never been used be certain to test on a small number of plants before applying to the entire crop. Be careful to use appropriate rates of copper compounds, with water at pH 6.0 or 6.5, since copper toxicity symptoms can look similar to those caused by the bacteria.

Current Research:

The current Xanthomonas outbreak on Ficus elastica has negatively affected many tropical foliage nurseries throughout Miami-Dade County. Plant losses are reported to be in the hundreds of thousands, so this is most definitely becoming an economically important disease.

The Palmateer lab is currently conducting research to 1) determine if Xanthomonas isolates from Ficus elastica are different from those previously reported to cause disease on other Ficus species; 2) conduct host range trials to see if other (i.e. Strelitzia spp., Ficus spp., Cordyline sp., Anthurium sp., Syngonium sp., and Dieffenbachia) popular foliage plants are susceptible; 3) evaluate the impact of temperature and light on disease; and 4) conduct bactericide efficacy trials.

Phytophthora diseases of ornamentals

The plant pathogen Phytophthora attacks all parts of the host plants, causing root and crown rots, and foliar and stem blights. Many Phytopthora species are pathogens on hundreds of hosts, including many important ornamentals. Phytophthera infestans caused the great Irish potato famine in the 1840's, which resulted in the death of 1.5 million people, and the immigration of another million to the United States. Once established in a nursery or landscape, it can be difficult to manage.

Common diseases of ornamentals caused by Phytophthora spp. in south Florida include stem and leaf blight of English ivy; root, stem and leaf blight of pothos and peperomia; root, crown and leaf blight of spathiphyllum; stem rot of dieffenbachia; foliar blight and root rot on anthurium and mandevilla; and root and crown rot of liriope.

Symptoms and Signs
Foliar symptoms of root and crown rots resemble those of nutritional deficiencies or overwatering, and include chlorosis, wilting, and defoliation. The plant canopy fails to thrive, indicating a problem with the root system of the plant. The root system itself may be stunted, with areas of brown and reddish necrosis, especially on feeder roots. The root cortex sloughs off easily, leaving the root stele.

Phytophthora also causes stem and foliar blights. These are irregular areas of necrosis on the stems and leaves that often are black and can cover large parts of the canopy. Phytophthora foliar blight can be distinguished from Rhizoctonia blight by the absence of mycelia, although heavy production of sporangia can be seen in necrotic areas in white patches. Symptoms of stem blights and crown rots can be seen on the right. Phytophthora also causes cankers and root rots on several large tree species.

Causal Agent
Although Phytophthora resembles a fungus, producing hyphae and spores, it is actually an oomycete and not in the Kingdom Fungi at all. It belongs to the stramenopiles, a group of protists that also contains diatoms and brown algae. Other plant pathogenic oomycetes are Pythium and the downy mildews (Peronospora, Plasmopora).

Like fungi, Phytophthora has an asexual and sexual stage. The genus produces lemon-shaped asexual sporangia that can wither serve as new inoculum or produce zoospores. These zoospores have a tail, called a flagellum, that they use like a whip to propel it through a film of water. Zoospores spread disease by swimming from infected to healthy tissue. See below left for pictures of an intact sporangium and one that is expelling its zoospores.
Under certain conditions, Phytophthora will undergo sexual reproduction and produce a round, thick-walled oospore. These spores can survive harsh weather conditions and so allow pathogen survival through unfavorable seasons, making Phytophthora diseases a perennial problem.

Disease cycle and epidemiology
Phytophthora survives dry, unfavorable weather in infected tissue or soil as oospores or another thick-walled spore called a chlamydospore. These spores germinate when weather is favorable for disease development and produce sporangia that in turn produce zoospores. The zoospores swim through films of water on the host and soil and infect susceptible hosts. In general, cool, wet weather favors disease development, although some species are more active at warmer temperatures.

Disease management
Sanitation is important in managing Phytophthora disease, because once a soil is infested with the pathogen, it can be very difficult to get rid of. All nursery stock should be inspected for symptoms before planting and pathogen-free soil should be used. Disinfect used pots and tools with a 10% bleach solution. Alternatively, soil, tools and pots can be sterilized with steam treatments.

Do not over water plants, as the disease is favored by wet conditions. Overhead irrigation encourages development of foliar blight by splashing spores within water droplets, and providing films of water on the foliage that the zoospores can swim through. Keeping foliage dry can limit the development of foliar blights.

If Phytophthora is a recurring problem, plants should be regularly scouted for disease symptoms. Diseased plants should be rogued and destroyed so as not to increase inoculum loads. In areas of the landscape infested with Phytophthora, only species that are not susceptible should be planted.

Several fungicides are available for control of Phytophthora. These may be applied according to the manufacturer label as part of an integrated approach that also follows the cultural practices outlined above.