There's a whole lot of fungus among the USS Cairo's wooden timbers. Scientists conduct study to help find ways to slow decay of historic ironclad at Vicksburg

The USS Cairo and an image of one of the fungus types found in the wood (Reprinted from Journal of Fungi); Claudia Chemello and Bob Blanchette examining Cairo timbers in 2024. (Paul Mardikian photo)

Confederate ships Little Rebel, Colonel Lovell and General Beauregard proved harmless, but Alternaria, Cladosporium and Curvularia are doing a real number on famed Civil War ironclad USS Cairo.

That’s because the latter are among a host of fungi eating away at the star attraction of Vicksburg National Military Park. The Cairo was the first armored vessel sunk by an electrically detonated torpedo and has been on display for decades.

A recent study found the wooden wreck is suffering continued fungal degradation, despite the application of chemical treatments over the years. Scientists who cleaned and examined the ironclad at Vicksburg National Military Park last year were alarmed by what they witnessed and have since analyzed.

“Finding so many fungi that cause wood decay alive in the ship timbers was a surprise,” said leader author Robert "Bob" Blanchette, a professor of plant pathology at the University of Minnesota.

Larger timber pieces inside the Cairo wreckage (Reprinted from Journal of Fungi)

“The wood surfaces are decayed and many of the timbers have had their strength properties compromised -- but many of the timbers are large and thick and still have moderately good integrity,” Blanchette wrote in an email to the Civil War Picket. “However, the presence of active decay fungi indicates they are progressively causing additional decay.”

The study, published in the Journal of Fungi, urges the Cairo -- which sits beneath a fabric canopy, but has open sides -- be moved indoors to a climate-controlled space to combat the toll from high humidity and heat.

Blanchette and his co-authors said keeping relative humidity below 55 percent would help arrest fungal action.

“An enclosed structure would also prevent dust, insects and animals from interacting with the ship. Undoubtedly, the condition of the wood will continue to deteriorate if the existing biodeterioration and biodegradation processes underway in the ship are left unaddressed,” they wrote.

The team was brought in by the National Park Service to evaluate the fungi and provide guidance on long-term preservation. The agency knows moving the ironclad indoors is necessary, but funding has not been secured.

Visitors can see gunboat during govt. shutdown

The Cairo and accompanying museum officially opened in 1980 (NPS photo)

The Picket reached out to the NPS and the park for comment on the study. An email said officials would respond to non-government shutdown queries once “appropriations have been enacted.”

Visitors to the park along the Mississippi River can still see the gunboat seven days a week. The Cairo museum has been open a few days but after Tuesday will be closed until the shutdown ends and money flows again to national historic sites.

Blanchette and Benjamin Held, also with the University of Minnesota, and Paul Mardikian and Claudia Chemello of Terra Mare Conservation say more study of the fungi is needed.

“Decades after various preservative treatments were applied, we now find soft rot and white rot fungi are in the wood,” Blanchette told the Picket. “Many of these fungi have not been studied and we do not know much about their biology and ecology. Others have received some investigation and some of these are known to tolerate various wood preservation treatments.”

The end comes in the Yazoo River above Vicksburg

The USS Cairo at anchor in 1862 (Library of Congress)

The USS Cairo’s fame has far exceeded its brief history. Built in a hurry in Mound City, Ill., and commissioned in January 1862, the ironclad sank only 11 months later. In between, it helped lead to the fall of Fort Pillow and Memphis, Tenn.

At 175 feet long and with a top speed of six knots, the vessel carried 13 guns and 251 officers and men. Seven shallow-draft City Class river ironclads prowled the Mississippi River and connecting shallow waterways, menacing Confederate supply lines and shore batteries, the National Park said.

Before the Federal attack on Haynes Bluff, Cairo skipper Lt. Cmdr. Thomas O. Selfridge Jr. led a small flotilla of gunboats into the hazardous confines of the Yazoo River on Dec. 12, 1862.

“Tasked with destroying Confederate batteries and clearing the river of torpedoes (underwater mines) the flotilla inched its way up the murky waters. As the Cairo reached a point seven miles north of Vicksburg the flotilla came under fire and the aggressive Selfridge ordered his guns to the ready and called for full steam, bringing the ironclad into action,” the NPS says.

“Seconds later, disaster struck. Cairo was rocked by two explosions in quick succession. The first tore and gaping hole into the port (left) bow of the wooden hulled ironclad. The second detonated a moment later near the armored belt amidships on the starboard side. The hole on the bow proved to be catastrophic.”

Selfridge ordered the Cairo to be beached and the crew to abandon ship. The Cairo slid from the river bank into 36 feet of water with no loss of life. About a half dozen sailors were injured.

Mud protected the ironclad for almost 100 years

The ill-fated ironclad disappeared into history for nearly a century.

Using maps and an old military compass, the legendary Ed Bearss, a historian at Vicksburg National Military Park at the time, and two comrades found the mud-encased ironclad in 1956.

A portion of the casemate rests on a barge in the 1960s (NPS photo)

Despite financial shortfalls, barge problems and a zero-visibility river that deposited silt at an alarming rate, the vessel was eventually raised in 1960 and 1964-65.

Hopes of lifting the ironclad and her cargo of artifacts intact were crushed in October 1964 when the three-inch cables being used to lift the Cairo cut deeply into its wooden hull. It then became a question of saving as much of the vessel as possible. The decision was made to recover the USS Cairo in three sections.

Barges carried the remnants to Pascagoula, Ms. The wreck was moved in 1977 to the Vicksburg park, where it was partially reconstructed and placed on a concrete foundation. The Cairo has been treated with a variety of chemical sprays and coatings since the 1970s. 

Frame that holds the Cairo's timbers in good shape

Diagram showing where samples were taken (Adapted from Library of Congress for Journal of Fungi article)

While submerged and under river sediments, bacterial degradation and soft rot took place, said Blanchette. After recovery, lots of different types of decay took place, including aggressive brown rot and white rot.

He and the other researchers gazed at the microstructure of the wood to see the effects of fungi. “Micromorphological characteristics observed using scanning electron microscopy showed that many of the timbers were in advanced stages of degradation,” they wrote.

They took 66 samples of wood – oak, pine and poplar -- from the wreck. “The large number of diverse fungal taxa that are present in the ship’s wood raises concerns about the future preservation of the ship,” the journal article said.

Blanchette (left) said fungi tolerant of preservation treatments applied to the Cairo found their way into the wood over time, causing decay.

 “The fungal isolation results and presence of so many fungi with the capacity to degrade wood also suggest that there is a need for additional studies to better understand how soft rot and white rot fungi tolerate and interact with aging wood that has been previously treated with wood preservation compounds,” the study said.

The park also asked the U.S. Forest Service to study the 1980s Glulam structure that holds the boat in place. It appears the frame is in pretty good condition, except for a few areas. (That team did not examine any of the ship’s timbers.)

Blanchette said his team did not find evidence of termites, though it did not include insects in the study. “As indicated in the Forest Products Lab paper, this must be monitored in the future since they can be a serious threat.”

The Forest Service also recommends moving the Cairo inside.

“The canopy currently is shedding precipitation from the actual frame, but the entire assembly is subject to substantial swings in relative humidity and temperature that could exacerbate issues with mold and decay fungi. The structure is also currently exposed to the risk of swarming insects such as termites, powder post beetles and carpenter bees.”