Friday, June 30, 2017

Pest Spotlight: Powdery Mildew

Crape Myrtle (Lagerstroemia x 'Zuni') with powdery  mildew. Neem oil extract horticultural oil can
help smother powdery mildew infections. Photo by J.S.Corser, Durham Co. Extension Master Gardener.

Clemson Cooperative Extension
Publication HGIC 2049

Powdery mildew is the name given to a group of diseases caused by several closely related fungi. Their common symptom is a grayish-white, powdery mat visible on the surface of leaves, stems, and flower petals. There are many hosts; and although this disease is not considered fatal, plant damage can occur when the infestation is severe.

Disease Cycle
In spring, as daytime temperatures rise above 60 °F, the fungi responsible for powdery mildew begin to produce spores (conidia) which are dispersed into the air. Infections occur when they contact a suitable host and environmental conditions are favorable. Initial symptoms are small, circular, powdery, white spots which expand and eventually join as infections progress. Infections spread as spores produced in these white patches move by wind and splashing rain to other locations on the plant or nearby plants.

The fungus survives the winter attached to plant parts and plant debris such as fallen leaves. As weather warms in spring, the process begins again.

Favorable Conditions
Humidity is an important factor related to the onset and spread of powdery mildew. Unlike most fungi, these do not require free water to germinate; only high levels of relative humidity. High relative humidity favors spore formation, and low relative humidity favors spore dispersal, which explains why powdery mildew tends to be a problem when the days are cool and the nights are humid. Temperature is also a factor. Although powdery mildew can occur all season long, it is less common during the heat of the summer.

Powdery mildew is caused by several different species of fungi, and they each have a limited host range. In other words, observing powdery mildew on oak leaves should not be cause for concern for nearby zinnias. Plants that commonly become infected with various powdery mildews include; azalea, crabapple, dogwood, phlox, euonymus, lilac, snapdragon, dahlia, zinnia, crape myrtle, rose, pyracantha, rhododendron, spirea, wisteria, delphinium, oak, English ivy, photinia, blueberry, pecan, cucumber, and squash.

As powdery mildew fungi grow over the plant surface, they develop structures that are inserted into plant cells enabling them to extract nutrients necessary for growth and spore production. This results in a general decline in growth and vigor of the host, as well as the common visible symptoms.

Abnormal growth, such as leaf curling, twisting, and discoloration may be noticed before the white signs of the fungus are visible. On dogwood, for example, leaves may take on a yellowish or reddish cast in summer or may develop reddish blotches or dead, scorched patches. The white powdery growth is not always apparent.

When visible, the powdery fungal growth can usually be found on the upper surface of the leaves, and tends to begin on lower leaves. As the disease progresses, leaves become dwarfed, curled and generally distorted. In severe cases, leaves will turn yellow or even dried and brown.

Powdery mildew fungi will also infect flowers, causing them to develop abnormally or fail to open. On azaleas and rhododendrons, small areas of dead tissue are often seen.

Powdery mildew creates other effects that are not readily visible. For example, a severely infected plant may have a reduced level of winter hardiness. Trees have also been observed to leaf out later in the spring after being infected the previous season.

Cultural Controls
As with all diseases, optimum plant health is the first line of defense. This begins with selection of healthy plants that are planted properly and in the proper location, giving attention to requirements for light, soil, and moisture. Space them so they are allowed to grow without being crowded and water thoroughly during establishment, and later during dry periods. Avoid overhead irrigation which raises the level of relative humidity within the plant canopy.

If powdery mildew is noticed on a few leaves, simply removing them will help with control. At the end of the growing season, prune out infected stems and remove fallen leaves which can serve as a source of further infection. Suckers are common on crape myrtle, dogwood and other plants. These should be pruned as they develop because they are especially susceptible and the disease will spread from them upwards to other plant parts.

Fertilize to optimize plant health, but avoid overfertilization with nitrogen as it stimulates young, succulent growth which is more susceptible to infection.
Plants with a severe infection should be monitored closely the following spring so that if infections reoccur, they can be treated early.

When possible, select plants that show resistance to the disease (see Table 1).

Chemical Control

Ornamental Plants: For fungicides to be effective, they must be applied as soon as symptoms are noticed. Product labels will provide information on how often to spray. When ranges are given, use the shorter interval during cool, damp weather. Be sure to cover both the upper and lower surfaces of the leaves.
Table 2 lists fungicides labeled for ornamental plants. Myclobutanil, propiconazole, thiophanate-methyl,  have systemic properties and can be sprayed less often than sulfur or copper-based fungicides. When powdery mildew persists and sprays are repeated, it is recommended to rotate (alternate) fungicides to decrease the chance of fungi developing resistance.
When deciduous plants are infected, consider the season. Generally, foliar diseases occurring in late summer do little damage. The leaves have already produced food for the plant and are going to fall off soon anyway. Just be sure to rake and dispose of them as they fall.
As with any pesticide, read the label and heed all precautions. Sulfur, for example, can damage plants if applied when temperature and humidity are high.
Vegetable Plants: For information on vegetable crop disease controls and tolerant varieties, consult the Clemson Extension publication EC 570, Home Vegetable Gardening, and other Home & Garden Information Center fact sheets.

Table 1. Plants with Resistance to Powdery Mildew.
Kousa dogwood, Cornus kousa‘Milky Way’, ‘Milky Way Select’, ‘National’
Cornus florida x kousa hybrids‘Aurora’, ‘Constellation’, ‘Celestial’, ‘Stellar Pink’
Flowering dogwood, Cornus florida‘Cherokee Brave’, ‘Springtime’, ‘Pygmy’, ‘Jean’s Appalachian Snow’, ‘Karen’s Appalachian Blush’, ‘Kay’s Appalachian Mist’
Crepe Myrtle: The Lagerstroemia indica x faurieri hybrids‘Apalachee’, ‘Fantasy’, ‘Hopi’, ‘Miami’, ‘Osage’, ‘Tonto’, ‘Tuscarora’, ‘Tuskegee’, ‘Wichita’, ‘Acoma’, ‘Sioux’, ‘Natchez’
Phlox‘David’, ‘Delta Snow’, ‘Natascha’, ‘Robert Poore’
ZinniaPulcino and African varieties, Zinnia angustifolia, Profusion Cherry, Profusion Orange
Hybrid Tea Rose‘Duet’, ‘Eiffel Tower’, ‘Grand Slam’, ‘Mister Lincoln’, ‘Tiffany’, ‘Jamaica’, ‘Matterhorn’
Floribunda Rose‘Golden Slipper’
Grandiflora Rose‘Camelot’, ‘Queen Elizabeth’, ‘John S. Armstrong’, ‘Pink Parfait’
Rugosa Rose‘Rugosa Alba’, ‘Blanc Double de Coubert’, ‘Fru Dagmar Hastrup’, ‘Topez Jewel’, ‘Alba’, ‘Alba Semi-Plena’
Monarda‘Marshall’s Delight’, ‘Cambridge Scarlet’

Table 2. Fungicides for Powdery Mildew Control on Ornamental Plants.
Active IngredientExamples of Brand Names & Products
Note: These active ingredients are listed in approximate order from most efficacious (best control) to least, but this also depends upon the plant and species of powdery mildew fungus.  Be sure to check the product label for which plants can be sprayed with that product.  For many vegetable crops, sulfur, copper-based products, chlorothalonil, horticultural oil, potassium bicarbonate and Bacillus subtilis can be used for powdery mildew control.
1 Do not apply sulfur if temperature is greater than 90 ºF or to drought stressed plants.  Do not use sulfur in combination with, or within 2 weeks before or after the use of horticultural oil treatments.  Sulfur will also control mites.
2 Do not apply horticultural oil if temperature is greater than 90 ºF.  Horticultural oil may injure Japanese, armur and red maples, cryptomeria, junipers, cedars, redbud, smoke tree and hickories. Add 3 tablespoons of horticultural oil to a gallon of water with 3 tablespoons of baking soda for better powdery mildew control.
RTS = Ready-To-Spray (hose-end sprayer).     RTU = Small, pre-mixed bottle.
MyclobutanilSpectracide Immunox Multi-Purpose Fungicide Concentrate
Sulfur1Safer Brand Garden Fungicide Concentrate; & RTU
Hi-Yield Wettable Dusting Sulfur
Southern Ag Wettable or Dusting Sulfur
Bonide Sulfur Plant Fungicide
PropiconazoleFerti-lome Liquid Systemic Fungicide II Concentrate; & RTS
Bonide Infuse Concentrate; & RTS
Banner Maxx Fungicide
Martin's Systemic Fungicide
Thiophanate-methylCleary’s 3336-WP Turf & Ornamental Fungicide
Southern Ag Thiomyl Systemic Fungicide
ChlorothalonilOrtho Max Garden Disease Control
Garden Tech Daconil Fungicide Concentrate
Hi-Yield Vegetable, Flower, Fruit & Ornamental Fungicide
Southern Ag Liquid Ornamental & Vegetable Fungicide
Tiger Brand Daconil
Ferti-lome Broad Spectrum Landscape & Garden Fungicide Conc.
Monterey Fruit Tree, Vegetable & Ornamental Fungicide Conc.
Bonide Fung-onil Concentrate
Horticultural Oil2Ferti-lome Horticultural Oil Spray Concentrate
Monterey Horticultural Oil Concentrate
Southern Ag ParaFine Horticultural Oil
Bonide All Seasons Spray Oil Concentrate
Neem Oil ExtractSouthern Ag Triple Action Neem Oil Concentrate
Ferti-lome Rose Flower & Vegetable Spray Concentrate
Garden Safe Fungicide 3 Concentrate
Garden Safe Neem Oil Extract Concentrate
Monterey 70% Neem oil Fungicide/Insecticide/Miticide Conc.; & RTS
Copper-based FungicidesBonide Liquid Copper Concentrate
Camelot O Fungicide/ Bactericide Concentrate
Monterey Liqui-Cop Fungicide Concentrate
Natural Guard Copper Soap Fungicide Concentrate; & RTU
Southern Ag Liquid Copper Fungicide
TebuconazoleBayer Advanced Disease Control for Roses, Flowers & Shrubs Conc.
Potassium BicarbonateBonide Remedy
Bacillus subtilisAgraQuest Serenade Garden Disease Control Concentrate

Caution: Pollinating insects, such as honey bees and bumblebees, can be adversely affected by the use of pesticides. Avoid the use of spray pesticides (both insecticides and fungicides), as well as soil-applied, systemic insecticides unless absolutely necessary. If spraying is required, always spray late in the evening to reduce the direct impact on pollinating insects. Always try less toxic alternative sprays first for the control of insect pests and diseases. For example, sprays with insecticidal soap, horticultural oil, neem oil extract, spinosad, Bacillus thuringiensis (B.t.), or botanical oils can help control many small insect pests and mites that affect garden and landscape plants. Neem oil extract or botanical oil sprays may also reduce plant damage by repelling many insect pests. Practice cultural techniques to prevent or reduce the incidence of plant diseases, including pre-plant soil improvement, proper plant spacing, crop rotation, applying mulch, applying lime and fertilizer based on soil test results, and avoiding over-head irrigation and frequent watering of established plants. Additionally, there are less toxic spray fungicides that contain sulfur or copper soap, and biological control sprays for plant diseases that contain Bacillus subtilis. However, it is very important to always read and follow the label directions on each product. For more information, contact the Clemson Extension Home & Garden Information Center.

Pesticides updated by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 10/16. Revised by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 11/09. Originally prepared by Chuck Burgess, HGIC Horticulture Extension Agent, Clemson University. New 09/05.

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Free Summer Harvest Classes for Briggs Ave. Community Garden

Briggs Avenue Community Garden.

Three exciting opportunities are coming up for learning about harvest at the Briggs Avenue Community Garden. The classes are free for Briggs Plot Owners and Master Gardeners. They will be conducted by Durham Co. Extension Agent Cheralyn Berry and Brandon Walton at the Durham County Cooperative Extension Office at 721 Foster St. in downtown Durham. Please email Pana Jones at or call 919-560-0525 to register for one or all of the classes.

Tomato Tasting with Craig LeHoullier, NC Tomato Man 
Saturday, July 15, 9 - 11 a.m.
Mr. LeHoullier has collaborated with Briggs Garden to grow out some of his newest genetic lines of tomatoes. Come hear him speak about his research and taste some of the newest tomatoes on earth. He will have his book, "Epic Tomatoes" available for sale.

Preserve the Harvest: Water Bath Canning
Saturday, July 29, 9 a.m. - Noon
Save the taste of summer the easy way by water bath canning. Delicious tomato sauce and pickles can be enjoyed all year round when you have the skills to make your own. Simple food science concepts will be explained for safe technique.

Preserve the Harvest: Pressure Canning
Saturday, Aug. 26, 9 a.m. - Noon
Many foods can be safely pressure canned for convenience and health. Enjoy delicious dishes your family will love by learning how to make them ahead in large batches to serve during busy weeks. Save freezer space and be prepared for winter power outages with a full pantry of tasty meals. Simple food science concepts will be explained for safe technique.

Friday, June 23, 2017

Burt's Bees Turkey Coop Permanently Installed in Durham

Burt's Bees HQ in American Tobacco District with Burt's Turkey Coop.
All of Burt Shavitz's antique and curious possessions were painstakingly moved from Maine and
arranged authentically as he lived.

Celebrate National Pollinator Week and visit the Burt's Bees turkey coop permanently located at the American Tobacco Warehouse District in Durham.

The relocation took approximately five months with the addition of air conditioning and a bathroom.

 Photos by J.S. Corser,
Durham Co. Master Gardener.

Pollinator topiaries installed outside
of the Burt's Bees turkey coop.

District 9 Presidents Meet in Durham for Annual Meeting

The Presidents Meeting of the District 9 of The Garden Club of North Carolina, Inc. met Thursday with over 30 District members representing 16 garden clubs in attendance.
The meeting was hosted by the Durham Council of Garden Clubs and was held at the historic John Sprunt Hill House. Meeting tables and the dining area were brightened by several floral arrangements created by State Secretary Pat Cashwell and Vice District 9 Director Catherine Phelps, both ladies hold national credentials as flower show judges. Gourmet tea refreshments were provided by Robin Marin of Town & Country Garden Club.
District 9 Director Marcia Loudon led the agenda and distributed an administrative binder to each club president or club representative. She presented critical dates, details, forms, etc. within the binders she created, emphasizing that all of the information can also be sourced on the GCNC website ( of which she is editor.
Past District 9 Director Andrea Lewis took a minute to promote the 2018 GCNC Annual Meeting, to be held April 15-17, 2018, in Chapel Hill, NC. “Orange You Glad It’s Spring?” is the theme created by the Orange County Council of Garden Clubs hosting the event. Andrea invited District 9 garden clubs to help volunteer for the meeting. Please contact her at:

Tuesday, June 20, 2017

BOOKS: The New Shade Garden

The New Shade Garden: Creating a Lush Oasis in the Age of Climate Change                             
Author: Ken Druse
Hardcover: 256 pages
Publisher: Harry N. Abrams (April 14, 2015)
ISBN-10: 1617691046
ISBN-13: 978-1617691041

From Amazon...

There is a new generation of gardeners who are planting gardens not only for their visual beauty but also for their ability to reduce carbon dioxide in the atmosphere. In The New Shade Garden, Ken Druse provides this generation with a comprehensive guide to creating a shade garden with an emphasis on the adjustments necessary for our changing climate. Druse offers advice for common problems facing today’s gardeners, from addressing the deer situation to watering plants without stressing limited resources. Detailing all aspects of the gardening process, the book covers basic topics such as designing your own garden, pruning trees, preparing soil for planting, and the vast array of flowers and greenery that grow best in the shade. Perfect for new and seasoned gardeners alike, this wide-ranging encyclopedic manual provides all the information you need to start or improve upon your own shade garden.

Friday, June 16, 2017

Outsmart the Weeds in Vegetable Gardens

Grow vigorous vegetable crops and manage them to outcompete weeds!

By Megan Gregory, EMG
Extension Gardener Newsletter,

With warm weather and rapid weed growth, many vegetable gardeners are reaching for hoes and spading forks. Gardeners can save labor by understanding weed life cycles and eliminating conditions that encourage weed growth (such as bare soil with excess nutrients). To outsmart the weeds in your garden, include practices in three categories of weed management:

1. Exclude weed seeds and propagules. Avoid bringing weeds into your garden by using only finished compost that has reached 140°F for a week or more, by using seed-free straw (rather than hay) for mulch, and by cleaning tools and equipment.

2. Use cultural practices to keep the soil covered and favor crops over weeds. Practice crop rotation. Vary when you till and plant because tillage stimulates weed seeds to germinate. To prevent summer annual weeds, establish an early spring crop. To prevent winter annual weeds, establish a long-season summer crop.

Grow vigorous vegetable crops and manage them to outcompete weeds. Use ideal planting dates and transplants to help crops grow quickly and shade the soil. Test your garden soil and apply only the nutrients you need for healthy crops, as excess nutrients will encourage weed growth.  Use drip irrigation or water at the base of your crops. Avoid watering between rows.
Include cover crops in rotations. Cover crops are sown between cropping cycles to enrich the soil and suppress weeds ( Once cover crops are cut down, the shoots can
be used as mulch around crops. Here are some tips on using cover crops to suppress weeds:
  • Plant summer cover crops (such as millet and cowpea) in May or June to outcompete  summer annuals and prevent germination  of winter annuals.
  • Plant overwintering cover crops (such as rye and hairy vetch) in the fall to outcompete winter annuals and to prevent germination of summer annuals the following spring.
  • Cover crops can also suppress creeping perennials like bermudagrass or nutsedge. Till the soil to fragment the weed, remove as much  as possible, and follow with a thick seeding  of the cover crop.

3. Use mechanical practices to block weed growth and kill weeds at critical times. Use mulches to deprive weeds of light. In vegetable beds, straw or cover crop residue can control annual broadleaf weeds. In paths, landscape fabric topped with wood chips can suppress bermudagrass. Use hand-weeding, hoeing, or shallow tillage sparingly. Attack weeds when they are small enough to be killed by hoeing or shallow tilling.  Avoid deep tillage, which brings weed seeds to the surface and damages soil structure.

For more information on weed identification and management, visit  With thoughtful planning, you can outsmart the weeds in your vegetable garden.

Wednesday, June 14, 2017

Durham Pollinator Garden Tour Features 13 Gardens: June 24

Celebrate National Pollinator Week by taking the Durham Pollinator Garden Tour on June 24!

Organized by Keep Durham Beautiful.
 Gardens on Tour:
  • Angier Avenue Neighborhood Farm...
  • Oak Church Garden
  • Immaculate Conception Community Garden
  • Edison Johnson Community Garden
  • NCCU Campus and Community Garden
  • Morehead Hill Community Garden
  • Briggs Avenue Community Garden
  • Sandy Ridge Elementary Garden
  • Lowes Grove Middle School Garden
  • Parkwood Community Garden
  • North Street Community Garden
  • Keep Durham Beautiful Demonstration Garden

Tickets can be purchased at:

Friday, June 9, 2017

Durham Celebrates National Pollinator Week (June 19-25, 2017)

The late Burt’s Bees co-founder Burt Shavitz in front of his turkey coop in rural Maine. The coop has been relocated to the Burts Bees headquarters in Durham's American Tobacco District. Photo Getty Images.
Durham is a certified Bee City USA and during Pollinator Week many local organizations will be hosting events to help raise awareness of the importance of pollinators and healthy habitat.
Come on out and learn about pollinators while having a great time!


Wednesday, June 21, Bee Downtown hosts the Bee Bash at the Durham Hotel from 6-8 pm
Thursday, June 22 and Friday, June 23, Burt's Bees will host tours from 10 a.m. - 6 p.m. Burt’s Bees will give tours of founder Burt Shavitz’s iconic cabin, a roughly 300 square foot converted turkey coop, at Burt’s Bees headquarters, American Tobacco Campus.
Saturday, June 24, Keep Durham Beautiful hosts a Pollinator Garden Tour from 9 am-1 pm. Tickets available for purchase
Saturday, June 24, Honeygirl Meadery hosts Wild Berry Mead Making from 2 - 4 p.m. at Honeygirl Meadery
Saturday, June 24, the Museum of Life and Science hosts Pollinator Day from 9 - 2 p.m.
Sunday, June 25, the Ellerbe Creek Watershed Association will be working to restore vital pollinator habitat and beautifying a new pollinator garden from 12 - 3 pm. RSVP for this volunteer opportunity

See Keep Durham Beautiful for links to register for Pollinator Week events:

Thursday, June 1, 2017

Hub Farm Receives $24K from Town & Country Garden Club

Town & Country Garden Club presented a $24K check in May to the Durham Public Schools Hub Farm. The monies came from proceeds of the garden club's 2016 Awesome Auction. Funds will be directed toward the purchase and construction of a teaching greenhouse.

Garden Product Spotlight: Avenger Natural Weed Killer

Avenger Organics Avenger Natural Weed Killer is a non-selective, post-emergence herbicide that quickly and effectively kills weeds, grasses and broadleaves without causing harm to the environment.

The active ingredient d-limonene (citrus oil) naturally strips away the waxy plant cuticle, causing it to dehydrate and die.

University and independent testing results prove that Avenger Weed Killer is as effective, but faster acting when compared against leading synthetic herbicides. When tested against non-organic ‘natural’ herbicides that contain vinegar (acetic acid), citric acid, clove oil or fatty acids (soap), it is more effective with quicker results.

June Calendar of Triangle Gardening Programs

What's on tap for June's educational and DIY gardening programs in the Triangle?
Check Triangle Gardener Magazine: