Fusiform canker in trees is caused by the fungus Cronartium quorum f. sp. Fusiforme (Cqf) and is a common disease in pines, particularly loblolly (Pinus taeda) and slash pines (Pinus elliottii var. elliottii).
Signs of Fusiform Canker include the formation of spherical or spindle-shaped galls on branches or main stems, serving as the most visible symptom on pine trees. Bright orange spores are often produced on the surface of these galls during cool spring months, aiding in the disease’s identification.
Effective treatment and management strategies involve preventive measures, such as avoiding planting susceptible species in high-risk areas and opting for relatively resistant seedlings.
What Is Fusiform Canker?
Fusiform rust is a significant forest tree disease that affects pines, particularly slash and loblolly pines, causing swellings (galls) on stems and branches, leading to deformities, reduced growth, weakened wood, and increased susceptibility to breakage
Fusiform rust is the primary disease constraining pine productivity across the southeastern U.S. Employing genetic resistance remains the sole economically viable means of control. Nevertheless, following a gene-for-gene pattern, interactions between the Cqf gene and its pine host hinder the successful application of resistance genes according to research done by Henry et al. (2021) on the Identification of Nine Pathotype-Specific Genes Conferring Resistance to Fusiform Rust in Loblolly Pine (Pinus taeda L.).
What Are the Symptoms of Fusiform Canker in Trees?
The symptoms of fusiform canker in trees include:
- The development of spindle-shaped swellings or galls on branches or main stems. On older trees, these infections are somewhat depressed on one side.
- The disease produces orange spores, weakening the tree and making it susceptible to secondary pests. Additionally, affected trees experience branch cankers within 12-18 inches of the stem, which grow into stem cankers, ultimately girdling and killing the tree.
- Yellowing and browning of needles around the cankers and the retention of killed needles on the tree by dried sap. Green shoots also wilt and die, giving the appearance of a shepherd’s crook.
- Cankers begin with some wound or cracking of the bark, and the tree’s natural defense mechanism usually resists most canker diseases, but stress makes the trees more susceptible to infection.
What Are the Types of Trees Vulnerable to Fusiform Canker?
Research conducted by DeepRoot shows that certain tree species exhibit greater susceptibility to climate change than others. The study categorized trees into “vulnerability classes,” assessing them based on dimensions scoring 40 or above.
Species deemed most vulnerable scored high across all three dimensions, with water locust, Texas walnut, Joshua tree, southern magnolia, and American basswood ranking as the top five in Vulnerability Class A. Conversely, coast redwood, red maple, and sweet gum were classified under Vulnerability Class E, signifying low current vulnerability levels.
Fusiform canker primarily affects pine trees, particularly loblolly and slash pines. It also affects other species, such as water, willow, laurel oaks, sweet gum, bluejack, blackjack, southern red, and turkey oaks.
Though, longleaf and shortleaf pines are relatively resistant to this disease. The infection leads to the development of galls or cankers on the main stem and branches, weakening the tree and making it susceptible to wind and ice breakage.
How Does Fusiform Canker Spread?
Fusiform rust spreads through fungus spores, which appear as a fine orange powder on fusiform swellings during early spring. Interestingly, these spores do not directly infect pine trees but are instead transported by the wind to oak leaves.
On these oak leaves, spores capable of infecting pine trees are produced. Various oak species, including water, willow, and laurel, serve as susceptible hosts for this transformation. While the rust may cause faint leaf spotting on oaks, it typically inflicts little to no harm.
Infected oak leaves develop brown, hair-like bristles on their undersides, containing microscopic spores released in late spring. Carried by the wind, these spores reach new pine needles and branch tips, initiating the fungus’s growth and subsequent infection of the pine tree.
Contrary to some beliefs, fusiform rust does not spread through the tree’s system, leading to the formation of new cankers. Each canker is a result of a distinct infection and affects only the specific area of the tree it infects. However, branch cankers pose a greater threat as they frequently extend downward into the trunk, potentially developing into damaging stem cankers over time.
This entire cycle occurs within a few weeks each spring, with most pine infections taking place in April and early May, particularly in regions like Georgia.
How Do I Minimize Losses from Fusiform Canker Damage?
To mitigate damage caused by fusiform rust, certain precautions are taken to reduce its impact on trees. By adhering to the following measures, the spread of infection is reduced effectively:
- Plant Stock: In nurseries, preventing fusiform infection involves spraying with fungicides like Ferbam, Ziram, or Bayleton from seed germination until early summer. Despite stringent precautions, occasionally infected trees still get shipped. Identify these seedlings by small, spindle-shaped swellings on their stems and discard them at the planting site.
- Planting: In areas prone to severe fusiform rust, consider planting shortleaf or longleaf pine, which exhibit greater resistance. Fusiform infection is more prevalent in sparsely stocked and rapidly growing stands. Hence, plantings need to be closer on better sites with expected rapid growth to encourage early natural pruning of lower branches, minimizing the spread of branch cankers.
- Young Stands: Early fertilization and cultivation stimulating spring growth heighten rust infection. Early thinning in young stands helps minimize losses from infected trees. Pruning out limb cankers within 15 inches of the stem saves many trees, limiting infection spread. Nonetheless, this practice is typically justified in high-value stands or over small areas.
- Older Stands: Studies suggest that loblolly pine sawtimber trees with up to half their trunk circumference infected by fusiform canker are retained in well-stocked stands with minimal risk of wind breakage. In such cases, the location of cankers and their impact on tree products are crucial.
- Homeowners: In areas with severe fusiform rust, consider selecting shade trees other than slash and loblolly pine. If these pines are vital to your landscape, protect them with a fungicide spray program until they reach at least 5 years old. Prevention is vital as successful treatment post-infection is challenging. Apply fungicides from May to mid-June for effective protection.
- Integrated Management: Integrated management approaches, such as hazard assessment and planting resistant seedlings, manage conifer populations at risk for disease.
Protect your trees from the threat of fusiform rust and ensure their long-term health and vitality. Take proactive measures today to mitigate the risk of infection and minimize damage. Whether you’re a homeowner or a nursery owner, implementing preventive strategies is essential. Contact us now to learn more about effective fungicide treatments and best practices for managing fusiform rust.
Are there any cultural practices that can help prevent fusiform canker?
Yes, several cultural practices encourage reducing the risk of fusiform canker. Avoiding tree wounds, especially during cool, wet weather when the fungus is most active, is vital. In addition, minimizing oak interaction and promoting proper tree spacing prevents the spread of the disease.
How does fusiform canker spread among trees?
Fusiform canker spreads primarily through spores released from infected trees. These spores are carried by wind or rain and infect nearby trees through wounds or openings in the bark. Birds and insects contribute to the spread by transferring spores from tree to tree.
Can fusiform canker be treated once a tree is infected?
While there is no cure for fusiform canker once a tree is infected, there are management strategies that mitigate its aftermath. Pruning infected branches, reclaiming affected trees during thinning operations, and using fungicides in nursery settings can slow the progression of the disease and reduce its spread.
