Extension Master GardenerSM Volunteers of Buncombe County

Plant Insects

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: Managing Bad Bugs in Your Vegetable Garden

Saturday Seminar presents:
Managing Bad Bugs in Your Vegetable Garden—Lessons from The Learning Garden

Squash Vine Borer adult_Lisa Brown_CC BY-NC 2.0_Flickr
Squash vine borer adult

Presenter: Laura Brooks, Extension Master GardenerSM Volunteer

Now that you’ve planted your vegetable garden, it’s time to discuss the nemesis of every veggie gardener: bad bugs!  Which ones should you look out for and what can you do about them?

Laura Brooks, co-chair of The Learning Garden’s vegetable plot located at the Buncombe County Extension office, highlights the three most common pests that were encountered last year in The Learning Garden: squash vine borers, flea beetles, and Mexican bean beetles. She describes the organic methods that Master Gardeners used to help ward off these pesky insects.  Laura explains the life cycle of these insects, what they look like from larvae to adult stages, when they emerge, and effective treatments.

To access this video on the Buncombe County Master Gardener website, click on the link:

Managing Bad Bugs in Your Vegetable Garden

Or go to www.buncombemastergardener.org, click on the ‘Resources’ tab at the top of the page and select ‘Gardening Videos’ from the drop down menu.

Pest Alert: Nantucket Pine Tip Moth

If you’re spending more time outside as the weather warms, you might notice problems in your landscape. One homeowner called the Garden Helpline about white webbing on the ends of some of the branches of a tree purchased as a live Christmas tree. She planted the tree in a special place in her yard as a reminder of that happy occasion. Although she knew it was a pine, diagnosing the problem required determining what pine species it was. The number of needles in each needle bundle can identify pine species. She reported that there were 3 needles in each bundle, helping identify the tree as a Scotch pine (Pinus sylvestris), a very popular Christmas tree species.

Scotch PIne three needle bundle
Three needle bundle pine

Damage: The description of the webbing she saw helped determine that her tree was infested with the Nantucket pine tip moth, (Rhyacionia frustrana). Other signs include:

• Deformed growth (stem crooking) or a reduction in growth (bushy or stunted growth);
• Fecal deposits may be present in the webbing on the outside of infested shoots;
• Trees can be killed when exposed to repeated Nantucket pine tip moth larval infestations.

Damage caused by Nantucket Pine Tip Moth

Identification:

• In North Carolina, this pest overwinters as pupae in hollowed out pine shoots;
• On warm days as early as January and February, new moths emerge to mate;
• Adult moths are 1/4 inches (6.3 mm) long with the head and body covered with gray scales. The forewings are covered with brick-red to copper-colored patches that are separated by irregular bands of gray and white scales;
• Adult females lay white to opaque eggs on shoots, needles, or terminal growth in spring;

Adult Nantucket Pine Tip Moth

• From 5 to 30 days later, young larvae (caterpillars) hatch from eggs and feed on the surface of new growth. These are 1/16 inches (1.6 mm) long, and cream-colored with a black head. They then move to the shoot tips, construct protective webs at the base of buds, and begin to bore into the bud or stem.
• Feeding continues inside the bud or stem until the caterpillars are fully grown in 3 to 4 weeks. The caterpillars then pupate inside the damaged stem.

Management:

• Proper watering, fertilization, and mulching practices to keep pine trees healthy;
• For minor infestations, you can hand prune infested shoots if branches are reachable.

Susceptible pine species:

• Other three needle bundle pines, which include pitch pine (P. rigida) and loblolly pine (P. taeda).
• Two needle bundle pines are highly susceptible to infestation. These include Japanese red pine (P. densifolia), mountain pine (P. mugo) and Japanese black ine (P. thunbergii).

Resistant pine species:

  • Eastern white pine (P. strobus) and Virginia pine (P. virginiana), which have five needle bundles.

                                        Article by Bob Wardwell, Extension Master Gardener Volunteer

For more Information:
Nantucket Pine Tip Moth: https://content.ces.ncsu.edu/nantucket-pine-tip-mo

How to Identify Pines: https://smallfarms.cornell.edu/2019/02/arent-they-all-just-pines-how-to-id-conifer-trees/

Contact Us

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

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