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diseases

Pest Alert: Basil Downy Mildew Found in Western North Carolina – July 22, 2019

July 29, 2019

Basil downy mildew has been confirmed on the variety ‘Genovese’ in the NC State University research plots in Haywood County, North Carolina.

Basil Downy Mildew Spores on Underside of Leaf
Basil Downy Mildew

Basil downy mildew characteristics

  • Pathogen: Basil downy mildew is caused by the fungus-like oomycete pathogen Peronospora belbahrii.
  • Host crop: Basil (Ocimum basilicum)
  • Host parts affected: Leaves are severely affected, which can result in yield reduction or plant death.

 Identification

The disease typically begins in June and lasts throughout the growing season. Symptoms include yellowing or browning of leaves, which may be mistaken for nutritional problems. Infected leaves have many dark spores on the underside of infected leaves that can be seen without a microscope or hand lens.

  • High-humidity and moisture—6 to 12 hours of moisture from morning dew, rain, or overhead irrigation.
  • Cool temperatures (60°F).

Prevention

The disease has not been found on the resistant sweet basil varieties ‘Thunderstruck,’ ‘Devotion,’ ‘Passion,’ and ‘Obsession.’ Planting these resistant varieties or pathogen-free seed of other varieties is essential to prevent basil downy mildew.

Some basil types are less susceptible than sweet basil varieties. Researchers have found red basil (‘Red Leaf’ and ‘Red Rubin’), Thai basil (‘Queenette’), lemon basil (‘Lemon,’ ‘Lemon Mrs. Burns,’ ‘Sweet Dani Lemon Basil’), lime basil (‘Lime’), and spice basil (‘Spice,’ ‘Blue Spice,’ ‘Blue Spice Fil,’ ‘Cinnamon’) to have less severe downy mildew symptoms.

In addition to infected seed. disease also spreads from airborne spores of Peronospora belbahrii. Help control by watering early in the mornings, so foliage dries quickly, and allowing enough space between plants to increase air circulation.

Disease control for home gardeners

Be diligent in checking basil leaves for downy mildew. Fungicides are most effective when applied in a preventive, weekly spray program. Products containing the active ingredients copper or chlorothalonil (‘Daconil’ is the trade name of one product with chlorothalonil) are the only effective products available to home gardeners. Apply to achieve good coverage on both sides of the foliage and apply the products before disease begins.

 For more information:

Pest Alert: https://plantpathology.ces.ncsu.edu/2019/07/basil-downy-mildew-found-in-western-north-carolina-july-22-2019/

Basil Downy Mildew: https://content.ces.ncsu.edu/basil-downy-mildew

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Categories Plant Diseases Tags basil, diseases, downy mildew, pest control, Symptoms

New Disease-Resistant Garden Roses Growing in Popularity

June 23, 2016

While European gardeners planted roses in beds with other plants and expected them to thrive without special attention, serious American rose gardeners focused on producing a few perfect flowers each season so they could win competitions. Fragrances, hardiness, and resistance to diseases such as black spot—a common fungal infection of roses—were cast aside for bigger, better-formed blooms. 

Roses_Tiffany_HybridTea_DiseaseResistant
‘Tiffany’ Disease-Resistant Hybrid Tea Rose

From disfavor to rose revolution
By the 1990s, American gardeners were no longer willing to take on these divas! For many of us, gardens were smaller and schedules busier. We had discovered organic gardening and pollinators and did not want to use toxic sprays. 

Then in the 1990s, David Austin roses reached the U.S. market, reintroducing easier-care garden roses with fragrance. In 2000, Knock Out® roses took the industry by storm. Their even easier care, long bloom season, and black-spot resistance appealed to yet more gardeners. Other rose hybridizers saw the huge market for disease-resistant roses, and began to create their own. Developing a new rose takes about ten years and a bit of luck. We are just now beginning to reap the benefits of the hybridizers’ efforts.

Roses_MotherOfPearl_Grandiflora_DiseaseResistant
‘Mother of Pearl’ Disease-Resistant Grandiflora Rose

Newer hybrids meet no-spray standard
American rose distributors have begun importing disease-resistant roses from Europe where there have been no-spray rose trials for years—many pesticides are banned in Europe. No-spray trials are now happening in the United States. ‘Sunshine Daydream’, a yellow grandiflora, was the first rose to win the All-America Rose Selection rose of the year under no-spray conditions. ‘Francis Meilland’, ‘Beverly’, and ‘Savannah’—all fragrant hybrid teas—have won awards in the Biltmore (no-spray) International Rose Trials here in Asheville.

Learn more
To learn more about roses, contact your local rose society. The Asheville Blue Ridge Rose Society serves Western North Carolina. Visit their website at www.ashevillerosesociety.org or contact them by email at rosesocietywnc@gmail.com.

The Buncombe County Extension Master Gardener Volunteers’ “Gardening in the Mountains” lecture series will present a talk on rose care and disease resistant roses at the County Extension office, 49 Mt. Carmel Rd., on Thursday, July 21, 11:30 to 1. Call 828-255-5522 to reserve a seat. 

Article written by Judy Deutsch, Extension Master Gardener Volunteer.

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Categories Roses Tags diseases, flowers

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