Prevent your pines from becoming gall-ridden, sick, and dying trees. Knowing how fusiform rust develops and spreads will help you take the necessary steps to keep your trees safe.
toddsmariettatreeservices.com gathered the following information, ways to identify, and control measures for fusiform rust.
What Is Fusiform Rust
Fusiform rust is a rampant and damaging disease of multiple pine species in the south and southeast. This lethal rust disease is caused by the fungus Cronartium quercuum f. sp. fusiforme. For this disease to complete its lifecycle and colonize a pine (Pinus) specimen, it must first find a host in the oak (Quercus) genus. The disease leads to rust galls and/or crippling cankers on pine tree trunks and/or branches.
Some of the more susceptible oak species include:
- Water (Quercus nigra)
- Willow (Quercus phellos)
- Laurel (Quercus laurifolia)
- Bluejack (Quercus incana)
- Blackjack (Quercus marilandica)
- Southern red (Quercus falcata)
While more than 30 pine species are affected by fusiform rust, the two most impacted species include:
- Loblolly (Pinus taeda)
- Slash (Pinus elliottii)
Fusiform rust is indigenous to the Southern States stretching from Maryland south to Florida and west to Arkansas and Texas.
Fusiform Rust Identification
The colloquial name of this fungus comes from the spindle-shaped (fusi-form) or tapered galls produced on pines at the infection site. In early spring, powdery, orange spores are produced by the fungus coinciding with the emergence of oak foliage.
In the tree’s weakened state, the following secondary pests may also appear:
- Black turpentine beetles (Dendroctonus terebrans)
- Coneworms (Dioryctria spp.)
- Pitch canker fungus (Fusarium moniliforme var. subglutinans)
Note: The most common way to identify fusiform rust is in early spring, when its galls on pines produce the signature orange, powdery spores.
Fusiform Rust Lifecycle
What makes this pathogen intriguing is that it requires an alternate host (oak) for the fungus to complete its 5-step lifecycle. Consider the following:
- In March, galls on pine trees produce aeciospores (the orange, powdery spores)
- The spores are carried by wind to infect emerging oak foliage
- In late spring or early summer, the oaks produce basidiospores on the underside of the infected foliage
- The spores formed on oak foliage are then carried by wind to the growing tips of pine trees
- The lifecycle of this clever pathogen completes as the pines are infected from late spring through early summer
This fungus may be unsightly during its lifecycle, but it does little to no harm to the oak foliage it colonizes.
Note: The annual timing of this entire lifecycle may vary depending on geographic location and when average temperatures are higher.
How Do You Treat Fusiform Rust
Fusiform rust management in a forest or landscape setting poses interesting challenges but can be accomplished over time with patience. Consider the following three control methods:
Oak Host Management – When seasonally appropriate, susceptible oaks (like those listed above) in and immediately adjacent to pine stands should be chemically treated, pruned, and fallen foliage collected and destroyed. Hire a professional tree service to help you suppress potential infections.
Although spores that infect pine species can be transported extremely long distances by wind, nearby infected oaks tend to account for most of the surrounding pine infections.
Pine Host Management – Avoid planting rust susceptible pine species in locations where fusiform rust is or has been an issue. Pruning branch cankers and removing diseased branches can help lower trunk infection potential. However, once the trunk is infected, branch pruning is not recommended. Diseased pine trees are not a direct risk to surrounding healthy ones since spores that infect pines come only from oak leaves.
If you are working with a dense planting site, hire an ISA-certified arborist to help you with sanitation thinning (of infected trees), creating an age-diversified stand, all while avoiding exceeding planting densities which may result in secondary insect infestations and infections.
Pathogen Management – Consider sanitation thinning where you have multiple pines growing. Remove pines with trunk galls and those riddled with branch galls. Pruning pines with multiple branch galls is not preferred or recommended. These pruning activities, when done from February through June, may result in the colonization of these pruning wounds.
Stand or specimen burning is not recommended. However, when burning is prescribed, avoid igniting resinous trunk cankers, which will likely end with charring and potential tree death.
Currently, one of the better fusiform rust management methods is prevention. This is best accomplished by planting (naturally or engineered) resistant pine species and treating oaks growing in the vicinity of your pines.
Fusiform Rust – Cronartium Quercuum f. sp. Fusiforme
In this article, you discovered information about fusiform rust, how it is identified, and several control methods.
Understanding the unique way this disease completes its lifecycle and how it is entirely dependent on a secondary host species will help you control it in forest, landscape, nursery, and planting for future harvest.
Neglecting to address fusiform rust will lead to the formation of galls and cankers that can severely weaken the tree, reduce its value for timber, increase wind susceptibility, and cause its death.
Photo credit: Robert L. Anderson, USDA Forest Service, Bugwood.org.