Fusiform Rust Never Sleeps

Disease of slash and loblolly pines persists in the southeastern United States

Multiple branch cankers such as those pictured here area symptomatic of fusiform rust disease. Photo by Robert L. Anderson, U.S. Forest Service, courtesy of Bugwood.org.
Multiple branch cankers such as those pictured here are symptomatic of fusiform rust disease. Photo by Robert L. Anderson, U.S. Forest Service, courtesy of Bugwood.org.

Fusiform rust, a fungal disease caused by Cronartium quercum f. sp. fusiforme, is the most damaging disease of slash and loblolly pines in the southeastern United States. There are currently over 60.3 million acres of slash and loblolly pine timberland in the Southeast, some of the most productive forests in the world. Forest managers rely on continued fusiform rust risk monitoring to choose which slash and loblolly pine stock to plant to avoid losses from the disease.

Newly published findings based on U.S. Forest Service Forest Inventory and Analysis (FIA) data show that though fusiform rust levels in slash and loblolly pine stands in some areas are lower than observed in the 1980s, in other areas the incidence of rust has changed very little in the last 30 years.

In 1972, annual South-wide losses from fusiform rust were estimated at around $28 million. Since then, millions of research dollars have been spent developing methods to select, breed, and outplant rust-resistant slash and loblolly pine stock.

Part of this effort included developing hazard zone maps for both slash and loblolly pine based on the analysis of FIA data. Published in 1997 in a report by Forest Service researcher Dale Starkey, the maps were widely used by forest pathologists, tree improvement specialists, and forest managers to make decisions about which planting stock to use on their lands.

As a result of decades of effort, productivity on pine plantations has doubled from what it was in 1940, and there’s been some evidence that rust incidence and tree mortality from the disease has been greatly reduced in areas once deemed “high hazard,” and especially on commercially owned lands where the best available genetic sources of resistance to fusiform rust have been planted.

Prompted by questions and statements from the field, KaDonna Randolph, research mathematical statistician with the Forest Service Southern Research Station FIA unit, was asked to update Starkey’s rust hazard maps using FIA data and evaluate changes in regional rust incidence between the late 1970s and the early 2010s.

Through the analysis of FIA data, Randolph and fellow researchers Ellis Cowling and Dale Starkey found that despite some decreases in fusiform rust incidence over the last 30 to 40 years, rust hazard remains high throughout much of the southeastern United States. They also found that rust incidence was about equal in planted and natural loblolly stands but was higher in planted versus natural stands of slash pine.

The results for slash pine were surprising. The reasons were unclear, but one reason may be the origin of planting stock, which was unknown and may be highly variable in terms of rust resistance.

Data from the analysis was used to update Starkey’s 1997 disease risk maps. The updated maps are included in the article and can be used to guide the planting of rust-resistant stock appropriate to specific areas.

“Because rust hazard remains moderate to high throughout much of the southeastern U.S. for both slash and loblolly pines, continued deployment of rust-resistant seedlings is recommended,” said Randolph. “It’s also necessary to continue rust research and monitoring programs so that the gains in genetic resistance achieved so far are not lost.”

Read the full text of the article.

For more information, email KaDonna Randolph at krandolph@fs.fed.us.

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