Extension Master GardenerSM Volunteers of Buncombe County

diseases

Galls in Your Garden? What to do!

Horned Oak Gall

Is there something weird growing in your landscape? I recently spotted this horned oak gall and knew I needed to find out what it was! Galls are something gardeners often notice—usually with alarm. What are they and do you need to do anything about them?

What are galls?
Unusual plant growths are often—but not always—galls.

  • Causes for gall growth include:
    • Critters—from adelgids and aphids to beetles, midges, mites, sawflies, and wasps
    • Bacteria and fungi
  • They affect many plants:
      • Trees
      • Shrubs
      • Perennials
  • And many plant parts:
    • Buds, flowers, and fruit
    • Leaves
    • Stems, twigs and branches
    • And even roots!
  • Galls may appear in different seasons, as well as change across seasons.
    • Azalea leaf gall - three stages of development. Photo by James H. Blake, courtesy of Clemson University Extension.
      Azalea leaf gall – three stages of development. Photo by James H. Blake, courtesy of Clemson University Extension.

      This spring you may have seen signs of azalea/camellia leaf galls (caused by Exobasidiumvaccinii/
      Exobasidium camelliae fungi) or maple eyespot galls (caused by Acericecis ocellaris midges) on your maple tree leaves.

    • Come summer you may have seen signs of crown gall (caused by soil bacterium Agrobacterium tumefaciens) on your roses, or oak apple galls (caused by wasps Amphibolips confluenta or quercusinanis) on your oaks.
    • As summer progresses, you may see evidence of life stages of horned oak galls (caused by Callirhytis cornigera wasps).
Horned Oak Gall leaf gall stage
    • Come fall and winter, goldenrod galls (caused by Eurosta solidagnis flies) are easy to spot.

 Which need attention?
It depends!

Aesthetics. Although galls may be fascinating, if you find them unsightly, you may want to remove them even if they will do no lasting harm to your plants.

Pros:

  • Removal may improve your plant’s appearance
  • Cleanup may help prevent further damage or disease.

Cons:

  • Removal may be impossible—think leaf galls that affect many leaves, such as Witch hazel cone galls.
  • Cleanup may remove the benefits to wildlife of some galls—birds feed on the larvae in goldenrod galls; birds, and some mammals, feast on the wasp larvae in oak apple galls.

Plant decline. Some galls left untreated will harm plants and may eventually kill them! Do not ignore Azalea/Camellia galls, crown galls, and horned oak galls.

What to do?

Prevention. When bacteria cause galls—crown galls, for example—there must be an opening to cause an infection. Careful handling to avoid wounding your plants as well as removing insect damage can help. Take care to clean and sanitize tools that might spread infection. Sanitation is also important for preventing fungal galls, such as Azalea/Camellia galls—dispose of diseased tissue in the trash, as well as clean any tools used.

Pruning is the answer to many aesthetic as well as more serious problems. Removing affected leaves or other plant parts may be all that is needed. In other cases, it may help, but it isn’t a cure-all. In the case of bacterial disease, for example, the cause of the gall is systemic and may or may not have a cure. Removal of early stages of horned oak gall wasp infestation can save trees.

Article by Buncombe County Extension Master GardenerSM Volunteers

 For more information:

Azalea/Camellia leaf galls: https://www.buncombemastergardener.org/time-maintain-remove-leaf-gall-azaleas-camellias/

Bacterial crown gall: https://extension.umd.edu/resource/bacterial-crown-gall-flowers

Horned oak gall wasp:

https://bygl.osu.edu/node/1019

http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=2922&Type=2

Goldenrod gall fly:

https://hort.extension.wisc.edu/articles/goldenrod-gall-fly-eurosta-solidagnis/

Maple eyespot gall: https://content.ces.ncsu.edu/maple-eyespot-gall-midge-acericecis-ocellaris-osten-sacken-diptera-cecidomyiidae

Oak apple gall: https://bygl.osu.edu/node/344

Sampling of gall photos:

https://projects.ncsu.edu/cals/course/ent525/close/gallpix/

https://www.maine.gov/dacf/php/gotpests/diseases/galls.htm

Series of American Nurseryman articles on galls:

https://www.amerinursery.com/plants/plant-galls-myths-misconceptions/

https://www.amerinursery.com/pest-management/insect-and-mite-galls-myths-and-misconceptions/

https://www.amerinursery.com/american-nurseryman/managing-galls/

 

Gardening Video: Tomato Problems, Diseases, and Pests

Gardening in the Mountains presents:
Tomato Problems, Diseases, and Pests

Check out the latest gardening video on the Buncombe County Master Gardener website. Learn how to identify and manage common problems that can affect tomatoes at all stages of maturity.  To access this video, click on the link below:

Tomato Problems, Diseases, and Pests

Or go to www.buncombemastergardener.org, click on the ‘Gardening Videos’ tab at the top of the page, and select the video from the list provided.

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

Contact Us

Buncombe County Extension Office
49 Mount Carmel Road
Asheville, NC 28806
Helpline 828-255-5522

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