Gall Rusts

Eastern (pine-oak) gall rust requires two hosts: pine and oak. The spores released from the galls on pines can only infect the leaves of oak. Damage includes shoot and branch injury.
Gall Rusts - Articles

Updated: November 21, 2017

Gall Rusts

Galls may produce spores each spring for up to 10 years. Courtesy of Tracey Olson, PDA

Eastern (Pine-Oak Gall Rust), Cronartium quercuum (Berk.) Miyabe ex Shirai
Western (Pine-Pine Gall Rust), Endocronartium harknessii (J. P. Moore) Y. Hiratsuka

Hosts

  • Two- and three-needle pines: Scotch, Austrian, Jack, Mugo, red, and Virginia
  • Alternate hosts: oaks for eastern gall rust

Damage Potential

  • Moderate–high

Symptoms and Signs

  • Stunting, deformation, and dieback of twigs and branches
  • Woody, globelike galls on branches or stem
  • Yellow-orange aecia (fruiting bodies) on surface of mature galls in spring

Causes of Similar Symptoms

  • None

Identification

Western (pine-pine) gall rust is the more common of the two in Pennsylvania, but eastern (pine-oak) gall rust can also occur. Both produce visible, globe-shaped galls on the stems or branches. The galls will increase in size each year and can end up being several inches in diameter. Around mid-May on 2-year-old and older branches, the blisterlike membrane of the fruiting structures (aecia) ruptures, covering the surface with a mass of powdery, yellow-orange spores (aeciospores). These spores are dispersed in the wind and will infect new plants. Western gall rust can easily re-infect the same tree and may result in multiple galls on the same tree and even the same branch. If a tree has a significant amount of galls, stunting and dieback of branches may occur and lead to death of the tree. Western gall rust may be especially lethal to seedlings.

Biology and Life Cycle

Eastern (pine-oak) gall rust requires two hosts: pine and oak. The spores released in the spring from the galls on pines can only infect the leaves of oak, the alternate host. Trees in the red and black oak group are especially susceptible. Once young leaves of oaks have become infected, a repeating spore stage occurs and the disease intensifies. By midsummer, spores that are capable of infecting only pines are then produced on the oak leaves. Absence of oaks in the growing area will break the required two-host life cycle and minimize the threat of this disease. Western (pine-pine) gall rust does not require an alternate host and is spread directly from one pine to another, infecting only new growth during the spring sporulation period.

For both diseases, spores are wind dispersed and infect new needles. The fungus grows into the shoots, where it establishes in the woody tissue of branches (Figure 1) and possibly the main trunk (Figure 2). Small galls may be visible after the first year; however, it may take up to 3 years for them to become large enough to be noticed (Figure 3).

Figure 1. Western gall rust on a branch (not sporulating). Courtesy of Susan K. Hagle, USDA Forest Service, Bugwood.org (#1241721)

Figure 2. Gall rust on the main trunk. Courtesy of Joseph O’Brien, USDA Forest Service, Bugwood.org (#5034007)

Figure 3. Gall forming at an infection site. Courtesy of Tracey Olson, PDA

Galls are formed due to an increase in wood production at the infection site. After the second year of infection, yellow-orange fruiting structures (aecia) will form on the surface of the gall (Figure 4). Galls may actively produce spores each spring for up to 10 years.

Figure 4. Powdery, yellow-orange spores on the surface of a gall. Courtesy of Tracey Olson, PDA

Monitoring and Management Strategies

Plantation Establishment

  • Avoid planting in fields adjacent to forest stands of oak or pines that show evidence of infection.
  • Plant disease-free nursery stock from a reputable source.

Preseason

  • Inspect seedling beds one year after planting. Remove any seedlings showing signs of galls.
  • In older plantings, remove branches with galls prior to active sporulation in mid-May.
  • If a tree is heavily infected with multiple galls or trunk dieback is visible, completely remove and destroy the tree before sporulation.

Growing Season

  • Scout fields to look for trees with branch and stem galls. For those that cannot be removed, monitor for presences of fruiting bodies.
  • At the end of the season, evaluate results and update records.

Control Options

Biological

  • No recommendations are available at this time.

Mechanical

  • Remove seedlings exhibiting galls from the field or cut out branches with galls from older, established trees. Do not move during period of spore production.

Biorational

  • No recommendations are available at this time.

Chemical

  • For western (pine-pine) gall rust, apply a registered fungicide to new growth of pines at the time of bud break to prevent infection. This must be applied before the fungus sporulates and releases the orange spores.

Next Crop/Prevention

  • Buy disease-free and/or resistant stock from a reputable nursery.
  • Rotate crop in the planting block to a non-susceptible tree variety.