Rose Rosette Mites Detected in Florida

First report of Phyllocoptes fructiphilus, the vector of Rose rosette virus in Florida.
by Xavier Martini, Austin N Fife, Gary Knox, and Mathews Paret

The eriophyid mite Phyllocoptes fructiphilus is the vector of Rose rosette virus (RRV), an emaravirus identified as the causal agent of the devastating Rose Rosette Disease (RRD). Incidence of RRD has grown exponentially, as the range of P. fructiphilus spread from the non-native, invasive wild rose, Rosa multiflora (Thunb) into other cultivated and uncultivated roses in the southeastern United States. In July 2019, P. fructiphilus was collected for the first time in Florida. Phyllocoptes fructiphilus is an established native pest of ornamental roses in the western United States and has become widely distributed in the eastern United States. However, the mite has never been previously found in Florida. RRV is currently not established in Florida. However, RRV infected plants have been identified on plants shipped for commercial production to Florida many times since 2013 and destroyed by UF-IFAS in collaboration with DPI-FDACS. Phyllocoptes fructiphilus were not present in any of these intercepted plants. This new confirmation of the presence of Phyllocoptes fructiphilus in the landscape is critical and warrants continued monitoring of the mite in Florida.

Description and biology

Eriophyid mites like Phyllocoptes fructiphilus are notable for their small size (140-170 µm long and 43 µm wide), carrot-shaped body and for having only four legs instead of the usual eight for other mites. P. fructiphilus lives on the new growth of buds and between stem and leaf petioles during the warm season. Mites overwinter under bark and old bud scales. Females begin laying eggs on shoots in the spring. Development from egg to adult takes 1 week. Adult females can live up to 26 days, and they can lay an egg each day. Therefore, these mites have the potential to build up to large numbers very quickly. P. fructiphilus lives and breeds on all cultivated roses, wild native roses and wild non-native roses such as multiflora roses.

Disease symptoms

It generally takes between 17 and 90 days for P. fructiphilus to transmit RRV to a rose. Symptoms appear 1 to 3 months after infection. As the mites are not visible to the naked eye, knowledge of how to recognize RRD symptoms is essential. Symptoms include: witches’ brooms (red small twisted leaves on elongated branches); severe thorn proliferation; leaf mosaic; distorted leaves and flower buds. Some of these symptoms can be misidentified and confused with herbicide damage or young leaf flush. In spring and fall, many healthy roses have reddened foliage; however, red pigmentation associated with RRD will persist for the life of the foliage. Plants usually die 1 to 2 years following infection.

Dispersal

Phyllocoptes fructiphilus dispersal is mostly aerial and the mite spreads via wind currents between plants. Therefore, the closer a rose is located to RRD roses the more likely it is to be infested, especially if the roses are situated downwind from the mite source. It is likely that humans also disperse these mites by moving infested plants or plant parts between different locations. Phoretic dispersal via insects and other animals is also possible but has not yet been demonstrated for P. fructiphilus. Another possible source of dispersion is by contaminated clothing and equipment.

Management

There is currently no cure for RRD. If a plant is infected, it is recommended to uproot (as the virus survives in the roots) and destroy the plant immediately. A new plant can be planted 7 days later in the same location, as mites do not survive more than 5 days without a rose host. To avoid spread of the disease, it is recommended to inspect roses for RRD symptoms before being purchased and avoiding entering areas with roses after coming back from an infested area. RRD can be transmitted by grafting but not by pruning.

Cultural control of mites

As dispersal of the mites is mostly aerial, walls and windbreaks may reduce P. fructiphilus dispersal and the spread of RRD. When planting roses, leave enough space between plants to prevent leaves from touching, which allows mites to crawl from one plant to another. Pruning will reduce mite populations, but prunings and fallen debris may contain mites. To prevent prunings from dispersing mites, it is critical to immediately bag prunings on-site and transport bagged materials for off-site disposal.

Chemical control of mites

Spirotetramat (e.g. Kontos®) and abamectin (e.g. Avid®)* based miticides include products labelled for eriophyid mite control in greenhouses and nurseries. Some studies indicate that carbaryl or bifenthrin based insecticides may effectively control P. fructiphilus. These chemicals can be found in some products labelled for use in landscapes and home gardens.

Scouting and collection

Due to their size, the mites are only visible under magnification. They can be found on leaf petiole bases and axillary buds, and are associated with fast-growing and soft tissues. There are a few different species of eriophyid mites that live on rose other than P. fructiphilus. Species identification can only be done under a microscope by a specialist. If the presence of either Phyllocoptes fructiphilus or RRD is suspected, please contact below before shipping. Collect the damaged/infested shoots and/or fruit and place them into a sealable polyethylene bag. Place paper towels into the bag (to reduce mold) and then carefully seal the bag before sending it to the following addresses:
Sam Bolton Division of Plant Industry/Entomology Florida Department of Agriculture and Consumer Services The Doyle Conner Building, 1911 SW 34th St, Gainesville, FL 32608 samuel.bolton@FreshFromFlorida.com 352-395-4679 or Dr. Xavier Martini University of Florida NFREC, 155 Research Road, Quincy, FL 32351 xmartini@ufl.edu 850-875-7160

Resources

For more information on RRD, please visit these sites: Rose Rosette Disease: A New Disease of Roses in Florida https://edis.ifas.ufl.edu/pp317
Roserosette.org

* Mentioning these pesticides does not signify endorsement or recommendation of any specific treatment option or chemical by the University of Florida.

Palm Management and OTC Injection Class

Agent Susan Haddock is holding a class on Palm Management and OTC Injections.  Here is the agenda and registration link:  https://www.eventbrite.com/e/palm-management-with-core-sampling-otc-demos-tickets-46205077631?aff=eac2

Palm Management

8 am-12 noon

This workshop will combine lecture and demonstration of palm sampling and OTC injection technique.

Agenda

8-8:50 am            IPM and Palm Management, Susan Haddock

9-9:50 am            Lethal Bronzing Disease Diagnosis (same as Texas Phoenix Palm Decline-TPPD)

                             Safely Sampling and Injecting OTC, Wayne Grubbs

10-11:40 am        Diagnosing and Correcting Palm Nutritional Deficiencies, Susan Haddock

11:45 am             CEU Distribution and adjourn

CEUs:

FDACS - 2.0 Core and 2.0 LLO, LCLM, L&O, O&T, LUF;  FNGLA - 4.0; Certified Arborist: 3.25; 
 Municipal Specialist: 3.25;  BCMA - Science: 3.25;  TW Climber Specialist: 3.25;  TW Aerial Lift Specialist: 3.25; 

Downy Mildew on Roses and Fungicide Treatments

Downy mildew on roses in Florida production areas is not uncommon.  This disease causes leaf spots which can cause significant defoliation.  The disease best grows with cool to warm weather (60-70 F) with high humidity and leaf wetness.   Here is a link to a good article on rose downy mildew from e-Grow with recommendations for preventative fungicide treatments.     https://e-gro.org/pdf/2017_719.pdf

Latest Pest Update

Here is the latest Pest Update for ornamental growers.  I would like to give credit to Lee Bloomcamp from Syngenta for taking the time to provide this information for growers.

Disease Issues

Leaf spots are prevalent now, as foliage ages and dies off.  Unless plants are going to be sold soon, treatment for foliar diseases is unnecessary, especially for deciduous plants.  Most leaf spot disease have long life cycles, and treating affected foliage now may not reduce leaf spot appearance.  Use a systemic fungicide as a drench to protect new growth as it emerges for better long term control, and use fungicides preventatively to keep infection from occurring.

Powdery mildew is active, recently seen on Mexican petunia, verbena, Gerber daisies, goldenrod, snapdragons, and crape myrtle.  This disease like cooler weather, with high humidity.  Scout regularly and maintain a preventative fungicide application program on vulnerable crops.  Mural, Palladium and Concert II are all very effective against  powdery mildew and leaf spots, other good choices for PM include Milstop, Eagle, and Phyton 27.

Downy Mildew is also showing up.  Salvias, basil, roses, coleus, and viburnum are some of the primary victims.  Downy mildew is systemic, meaning that it lurks in the plant until conditions are right for spore production.  That’s why fungicides are best used preventatively, curative rescue applications are often too little, too late for this fast-moving disease.  Limiting leaf wetting, increased spacing and airflow, and removal of severely infected plants is also important.

Phytophthora, Volutella and other systemic stem and root diseases continue to be a problem across Florida.  Extreme summer heat and the need for lots of irrigation are contributing factors.  In woody plants and some herbaceous material, cutting in to the stem tissue can help with diagnosis- discolored tissue indicates possible Phomopsis, Volutella or other die-back diseases like Phyllosticta  and Pestalotiopsis.  Roots are often unaffected.  With Phytophthora, roots are often discolored, and little to no evidence is found in woody tissue.  Segovis is an outstanding addition to phythophthora rotations- fully systemic, drench and foliar applications, low use rates and a 4 hour REI.  Bacterial disease symptoms can look like both.  Consider getting a disease analysis done if problems are severe, as a number of things can cause general dieback associated with these diseases. Specific fungicides and cultural controls are needed, and time and money can be wasted on the wrong products and techniques!

Sanitation is key to disease prevention- clean up old, diseased leaves and cuttings to reduce inoculum, and be ready to treat new growth as soon as it appears.  This is when many disease cycles begins, even if damage doesn’t appear until  foliage has matured.  Send samples off for diagnosis if problems are persistent.  Knowing the disease involved helps to determine the best timing, cultural controls and fungicides for preventative applications.

I am also seeing secondary foliar symptoms that look like disease but are related to nutritional issues.  Summer weather can deplete nutrients in even the best slow release fertilizers, and some micronutrient deficiencies can result from extreme soil pH conditions, and look like disease problems.  Proper diagnosis of the problem leads to a quicker resolution- did I mention this already?

Insects and Mites

Caterpillars are evident in many crops this time of year.  Species like Fall Armyworm, European Pepper moth and Cutworms have spring and fall population peaks, so check plants like ferns, poinsettias, bedding plants, gingers and other herbaceous perennials for caterpillar damage.  Webbing, droppings and foliage damage at the soil line are good indicators.  If uncertain, take the entire plant and soil out of the pot, and break it up into a bucket of water.  Larvae, pupae, webbing and other debris will float to the surface for easy ID.

Water floatation is also a good way to survey for Azalea root weevil, and Flea beetle grubs, which often attack the roots of the same plants that host adults feeding on foliage. Grower feedback on Mainspring GNL for caterpillar and flea beetle control has been very good, looks like we have another tool for these pests!  Mainspring GNL is labeled for foliar and drench applications, is systemic, and also has a 4 hour REI.


(Disclaimer-Mention of a commercial or herbicide brand name or chemical does not constitute a recommendation or warranty of the product by the authors or the University of Florida, Institute of Food and Agricultural Sciences, nor does it imply its approval to the exclusion of other products that may also be suitable. Products should be used according to label instructions and safety equipment required on the label and by federal or state law should be employed. Pesticide registrations may change, so it is the responsibility of the user to ascertain if a pesticide is registered by the appropriate state and federal agencies for its intended use.)

UF/IFAS Online Course on Disease Management for Growers

Would you like to have a better basis for what is going on with plant diseases and how to treat them?  We have a class for that.  We are less than 3 weeks away from the start of the next class on the Greenhouse Training Online series, Disease Management. The class begins on September 26^th and you can register up to October 3^rd. 

For more about how the class works and pricing go to the direct link  at http://tinyurl.com/DiseaseMgtHills2016

This course will train you to:

Learn how plants become infected, what factors contribute to plant disease development and what are the different options available for diagnosing and controlling diseases in the greenhouse and nurseries.
Learn fungicide formulations and accurate rate calculations.
Know rules and regulations of handling fungicides.
This is an intermediate level (some experience and training, entry level university).

If you have questions about the registration process, please email greenhousetraining@ifas.ufl.edu. Also, if you are registering 5 or more students from the same company or organization then contact greenhousetraining@ifas.ufl.edu for a quicker registration process.

Boxwood Blight Found in Florida

Boxwood blight is a devastating boxwood disease and it has just been found in North Florida.  A disease alert has been issued from UF/IFAS and FDACS DPI.  If you grow or purchase boxwood please take a moment and read the alert found at the link below.   There has been a bunch of research done in North Carolina on the cultural control, variety selection, and chemical control which can also be found at the same link.  If you suspect you might have problems please give Extension a call.  Photo credit Mathews Paret. link. http://hillsborough.ifas.ufl.edu/ornamental_production/index.shtml  

Sugarcane Mosaic Virus in St Augustine Grass

Photo from Phil Harmon EDIS #PP313

Here is a disease that has been showing up lately in our local area (Pinellas County) and growers should be aware of.  Mosaic disease of St. Augustinegrass was first reported in the 1960s in sugarcane producing areas of Palm Beach County, Florida. In September 2013, an outbreak of the disease occurred in Pinellas County. Leaf symptoms included mosaic, but turned necrotic and the severe dieback that completely killed some infected lawns.  Previously infected lawns as well as new ones started dying in both Pinellas and Palm Beach Counties. As of November 2014, all samples have tested positive for presence of Sugarcane Mosaic Virus. This 3-page fact sheet was written by Phil Harmon, and published by the UF Department of Plant Pathology, November 2014.  Here is a link to the factsheet.  http://edis.ifas.ufl.edu/pp313

If you are a sod producer and suspect that this might be happening in your production field let your local Extension Agent know.

Scouting Help from North Florida

Dr. Mathews Paret from the UF/IFAS Quincy Research and Education Center has some really good disease information resources that can be used for your own information or for some of your crop scouting.  Please scan below to see what is available on his U-scout web page.

New in Plant Disease Blog:  http://nfrec.ifas.ufl.edu/paret/u-scout/Blog/Blog.html
Phytophthora crown and root rot of scotch bonnet
Phytophthora root rot of boxwood
Phytopthora root rot of gardenia
Daylily rust

New in Extension Tutor:   http://nfrec.ifas.ufl.edu/paret/u-scout/Tutor.html

Latest field trial data on bacterial spot, bacterial wilt, target spot and root-knot nematode management on tomato.
Latest field trial data on gummy stem blight (watermelon), powdery mildew (watermelon, cantaloupe), and Phytophthora crown and root rot of squash.
Latest field trial findings on management of diseases of crape myrtle using resistant varieties
History and present status of watermelon rind necrosis

This section also includes tutorials on many other aspects: hands on identification of tomato and cucurbit diseases, Florida and South Eastern Vegetable production handbooks 2014, rose and cucurbit diseases and management, and other topics on plant disease management.

Plant disease databases: Databases includes 100s of pictures of vegetable diseases (tomato, cucurbits, pepper, and brassica crops) and ornamentals (rose, crape myrtle, hydrangea, and magnolia). Most of the pictures are field shots and reflect how you may see the disease in the field.

Tomato:  http://nfrec.ifas.ufl.edu/paret/u-scout/Tomato/Tomato.html
Cucurbits:  http://nfrec.ifas.ufl.edu/paret/u-scout/Cucurbits/Cucurbits.html
Pepper:  http://nfrec.ifas.ufl.edu/paret/u-scout/Pepper/Pepper.html
Brassica:  http://nfrec.ifas.ufl.edu/paret/u-scout/Brassica/Brassica.html
Rose:  http://nfrec.ifas.ufl.edu/paret/u-scout/Rose/Rose.html
Crape Myrtle:  http://nfrec.ifas.ufl.edu/paret/u-scout/Crapemyrtle/Crapemyrtle.html
Hydrangea:   http://nfrec.ifas.ufl.edu/paret/u-scout/Hydrangea/Hydrangea.html
Magnolia:   http://nfrec.ifas.ufl.edu/paret/u-scout/Magnolia/Magnolia.html

Disease Watch section for tomato, cucurbits, rose and hydrangea for Fall 2014 is issued and details can be found in the following link.
http://nfrec.ifas.ufl.edu/paret/u-scout/Disease_Watch.html

Pest Alert: First discovery of Rose Rosette Virus in Florida
http://nfrec.ifas.ufl.edu/paret/u-scout/Pest_Alert.html

New Factsheets from UF/IFAS

There are a few more factsheets for your perusal from IFAS EDIS our Electronic Data Information Source.  This week we've got factsheets on trees, diseases and weeds for your reading pleasure. 

This one is entitled Plumeria:  Propagation from Cuttings http://edis.ifas.ufl.edu/pdffiles/EP/EP48900.pdf
Here is one on identification and control of Impatiens Downey Mildew  http://edis.ifas.ufl.edu/pdffiles/PP/PP30900.pdf 
Here is a factsheet on one of the weeds that I see at nurseries everywhere. Erect and Prostrate Spurge Managenment in Turf. http://edis.ifas.ufl.edu/pdffiles/EP/EP49500.pdf
This is one on a unique tree I haven't seen before. Faber's Maple:  Acer fabri http://edis.ifas.ufl.edu/pdffiles/EP/EP49000.pdf
And here is one on Apalachee Crapemrytle:  Lagerstromia idica x fauriei 'Apalachee' http://edis.ifas.ufl.edu/pdffiles/EP/EP49100.pdf

New Virus in Roses for Florida

Rose Rosette Virus is a disease that has been around for a long time but has just been identified in Florida from a nursery in Quincy, in Knock-Out roses.   This virus is transmitted by microscopic mites (Eriophyid mites). The virus causes a proliferation of thorns and abnormal growth (witch's broom symptoms).  As of January, it was also found in Gadsden, Alachua, and Levy counties in Florida.  The disease will usually kill infected plant within 1 to 2 years.  Growers should be scouting for this new disease as DPI will quarantine a nursery with this virus until there is no more apparent risk at the site.  If you suspect that plants have the symptoms, you can submit them for proper identification at a UF plant disease clinic.  Growers should destroy infected plants. UF is recommending the use of insecticides for Eriophyid mite control in the early spring.  Always rotate Modes of Action!  For a general overview about the disease and pictures of symptoms, here is a link you can take a look at http://entomology.ifas.ufl.edu/news/2013-2014/RRV_PestAlert_Paret_2014.pdf.  For an extensive amount of grower information about Rose Rosette Virus, check out the site www.roserosettedisease.com.  For more information about the mite vector, here is a link to an EDIS publication http://edis.ifas.ufl.edu/pdffiles/IN/IN99900.pdf  Information from the above sources were used for this article.

Plant Disease Control Workshop

Here is an ornamental disease seminar you may want to attend from BASF at the Gulf Coast Research and Education Center in Balm on June 28, 2012.  CEUs will be available.

Disease Control and Plant Health Strategies in Ornamentals
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

For More Information Contact:  Brian McCaffrey 727.858.0983, brian.mccaffrey@basf.com or Frank Fornari, 352.630.0123, frank.fornari@basf.com

Click on this link to register.
http://www.eminj.com/BASF/PageantIntrinsic/Registration.cfm

Downey Mildew on Impatients

This was an article from Greenhouse Grower.  I have been hearing a bunch about this disease on impatients but haven't seen it yet.  There are a few pictures from the article if you go to this link.
http://www.greenhousegrower.com/article/24846/your-impatiens-might-have-downy-mildew-if-


By Laura Drotleff  Feb 7, 2012
Growers across the country are scrambling for solutions, with the discovery of downy mildew on impatiens in the U.S. landscape. Look for these symptoms in the greenhouse when you’re scouting your impatiens crop this year:
• Plant foliage that’s yellowish or pale green in color
• Leaves that curl downward
• Leaves that are distorted
• Undersides of leaves that have white or light gray fuzz present
• New and emerging leaves that are small and a discolored yellow or pale green
• Flower buds that fail to form
• Stunted plant growth


If you see one or more of these symptoms on a plant, immediately seal it in a plastic bag before removing it from the greenhouse. Get it to a diagnostic lab for further testing.
Additionally, when spraying for downy mildew, there are three important things to remember when applying fungicides:
1. Apply fungicides preventatively.
2. Rotate among products with different modes of action to prevent resistance.
3. Be timely in re-applications.


Laura Drotleff is a freelance writer based in Willowick, Ohio. She spent seven-plus years as an editor on Greenhouse Grower. Reach Drotleff at ldrotleff@gmail.com.

Diaprepes Root Weevil in Ornamentals

I have recently been to a couple of tree producers and have seen the dramatic effects of diaprepes root weevils in their nurseries.  Above is a picture of a dead holly tree that seemingly had root damage caused by both insects and disease.  These medium-size insects can have devastating results to larger grown material. The adults can be seen in ornamentals by the damage they inflict by notching the leaves.  Usually this is not bad enough to render a plan unsalable, but it is a good indicator of the insect and of the need to treat it. The bad stage of this insect infestation is what lies below the ground unseen.  The juvenile stage of this insect is a root grub that will girdle roots of plants and trees. If infestations are extremely high plants may show symptoms of lack of vigor and even death. Along with root girdling, plants may become infected with soil borne pathogens usually this is Phytophthora. Roots become susceptible when the juveniles wound the roots and allowed root exudates and carbohydrates to leak and  feed pathogenic fungi.  These fungi when weather conditions permit can become extremely aggressive infecting roots and causing tree death.  Here is a link to a publication on diaprepies  http://edis.ifas.ufl.edu/in147  and here is a link to host plants that can harbor the pest  http://edis.ifas.ufl.edu/in119  Here are some pictures of root damage and fungal infection probably caused by the insect/disease complex on holly.

Integrated Pest Management Update

Hillsborough County Extension will be hosting the Integrated Pest Management Update on January 25, 2011 at the UF/IFAS Gulf Coast Research and Education Center in Balm. The Integrated Pest Management Update Program is an award-winning statewide event that helps green industry professionals and nursery growers correctly identify pest problems and to utilize the latest, best management practices to treat them. This event cycles alternating years between landscape and grower themed issues. This year's event will deal mainly with landscape issues but would have numerous cross-over topics for growers as well. We try to help you put all the pieces of pest mangement together.

$2o.00 plus $2.09 online registration fee includes resource materials and refreshments at the event.

FNGLA, CCA, and FDACS, CEUs are Available!

Here are the topics below:

12:30 - 2:00 pm Distinguishing landscape disease & insect problems from environmental stresses
Landscape / Ornamentals – Dr. Catharine Mannion
Turfgrass – Dr. Young-Ki Jo
Palms –Dr. Monica Elliot

2:00 - 2:30 Diagnostic Tools
Utilizing a web based diagnostic and identification system (DDIS) for solving plant problems - Dan Culbert

Developing a plant diagnostic toolbox for use in the landscape - Ed Skvarch

2:30 – 3:30 pm Use of Biorational products for landscape & turf management – Dr. Eileen Buss

3:30 – 4:30 pm Vendor Presentations - The latest chemical industry updates on new products for the green industry.

If you are interested in attending this event please register and click on the link below

http://ipmu01252011.eventbrite.com/

For more information please contact Shawn Steed 813-744-5519.

Diseases and Insect Lessons From 2010

Here is an interesting Webinar sponsored from Miester Media Worldwide, as a grower you might like to listen to. You might find out what pests others are dealing with and how to cope with them.

Nancy Rechcigl, technical manager for Syngenta, will discuss some of the major disease and insect pressures growers are experiencing in 2010. From mums to pansies to poinsettias, her presentation will include an analysis of common issues growers faced and tips and preventative treatment options for next year.

Title: Disease And Insect Lessons From 2010

Date: Wednesday, December 8, 2010

Time: 2:00 PM - 3:00 PM EST

Space is limited.Reserve your Webinar seat now at:https://www1.gotomeeting.com/register/662612097

After registering you will receive a confirmation email containing information about joining the Webinar.

System RequirementsPC-based attendeesRequired: Windows® 7, Vista, XP or 2003 Server

Macintosh®-based attendeesRequired: Mac OS® X 10.4.11 (Tiger®) or newer

Fusarium Wilt of Queen and Mexican Fan Palms

This disease affects queen and Mexican fan palms. The causal agent is Fusarium oxysporum (palmarum). The disease starts out on the older leaves first and only affects one half side of the frond at first. The palm dies quickly within a few months after the initial symptoms. Here is an updated Fact Sheet on Fusarium Wilt of Queen and Mexican Fan Palms.

http://edis.ifas.ufl.edu/pp278

Powdery Mildew on Oaks

I've noticed indications of powdery mildew on "Cathedral" live oaks pp #12015 recently at a field visit to a tree farm. If you are growing this variety of oaks you may want to do some scouting and check the leaves for the presence of this disease. It would also be good to set a threshold limit for economic damage.

A picture of affected "Cathedral" live oak leaves.

Determine how much damage is acceptable before treatment is necessary. I have seen defoliation of this cultivar later in the growing season that might be attributable to this pathogen growing unchecked. This potentially took the affected trees out of availability for sale until new leaves could be grown in the spring. Here is a link to a publication on treatment for powdery mildew.

Professional Disease Management Guide for Ornamentals http://edis.ifas.ufl.edu/pp123

and here is a publication on powdery mildew on gerbera daisy with a list of fungicides that that can be used for ornamentals. http://edis.ifas.ufl.edu/pp257

Make sure that if you decide to spray you read the label for proper rates!