The Sinner’s Tree Diseases

It’s rare that tree diseases show up in fiction, so it’s surprising that one television series mentions more than one. The Sinner is a moody crime series originally on USA Network, but found on Netflix and probably elsewhere. In an interesting twist, it is a “whydunnit” rather than “whodunnit” — the perpetrator is clearly revealed in the first episode of each season.

Bill Pullman is marvelous as Detective Harry Ambrose, a shy introvert, awkward with people but at the same time able to connect in a way few people can, and carrying a lot of guilt since childhood. He speaks in a soft, halting stammer, especially when talking about himself, and least when talking about trees, when he seems to light up. He has knowledge of and interest in trees and their diseases that occasionally pops out, an interest that is often portrayed as eccentric and odd, but also useful to disarm or distract witnesses or suspects.

White pine blight

In the very first episode (S01E01), he’s at the crime scene on a lake shore, with a forest visible on the far side. From the script:

A beat. Ambrose squints into the distance. It’s hard to tell if he’s thinking deeply, or uncomfortable, or both. His eyes trace the edge of the beach.

Ambrose: Pinus strobus.

Belewski: Hmm?

Ambrose: You see those white pine across there? They got a blight . . . An ecosystem out of balance . . .

Leroy and Belewksi look at the trees, not sure what to say.

Of course Leroy and Belewski don’t know what to say, but we do. Beginning in 2009, an unusual, novel foliage discoloration of Pinus strobus (eastern white pine) was observed in eastern Canada and northeastern USA, as far south as Virginia ​[3, 8, 10]​. It was attributed to Lophophacidium dooksii in some cases and to Canavirgella banfieldii in others, but it was later found that those are really the same fungus ​[8]​. Several additional pathogens were found, including most notably Mycosphaerella dearnessii, cause of brown spot needle blight ​[10]​.

Another interesting aspect of this is that the two fungi, found to be one and the same, had been placed in completely different orders! And the disease caused by C. banfieldii (Rhytismatales: Rhytismataceae) was called a needle cast, while that caused by L. dooksii (Phacidiales: Phacidiaceae) was called Dook’s needle blight. When their identity was determined ​[8]​, the molecular evidence suggested that L. dooksii really belongs in Rhytismataceae, in the genus Lophodermella. That was confirmed recently in a study of the genus ​[2]​, and it’s probably a matter of time before the species is formally given the new combination, Lophodermella dooksii. As the disease cycle was also recognized as that of a typical needle cast by a real expert ​[9]​, the disease should be called Dook’s needle cast.

It appears that changes in precipitation patterns led to the increase in foliage diseases ​[10]​. Since the chief pathogen, L. dooksii, had never been noticed and described until the 80’s and 90’s, the weather patterns may be a significant departure from the past: “an ecosystem out of balance.”

It’s a Hevea brasiliensis

Later in that same episode, our hero is interviewing a witness in the hospital. The witness is trying to extricate himself, when Detective Ambrose identifies a plant problem. See the video clip.

Ambrose then goes on to another tactic to keep the witness talking. I know, not quite as electrifying as a novel foliage disease in the forest, but still . . .

Fertilizing his ex-dogwoods

This one is more about disease prevention, in S01E06. Harry is separated or divorced, but he had planted dogwoods at their house and he still wants to care for them. You can feel the emotion and pain in his voice. Is it only the loss of the marriage that he feels, or also the thought of abandoning the dogwoods?

Schooling the suspect on dogwoods

Our Forest Pathologist Detective Ambrose manages to get through season 2 with no tree disease encounters, as far as I recall. In S03E02, he’s tailing Jamie and pretends to bump into him in a retail nursery. Jamie is picking up a dogwood tree to mark his son’s imminent birth. As described on ew.com:

“Ambrose trails him to the nursery under the guise of grabbing some gardening goods for himself. It’s at this point we learn Harry’s not only a perceptive sleuth, but he also possesses one hell of a green thumb.

“As a dumbfounded Jamie gets schooled on seeds, soils, and roots, he nervously inquires as to why the accident’s being investigated. Harry steers the conversation to get a definitive “no” from him on whether Nick’s visit was planned. Brilliant detective that he is, he also parlays the encounter into a weekend date to help Jamie plant that tree.”

The nugget in this interaction is Harry’s warning about dogwood anthracnose. “You really want the Kousa, because it’s immune to anthracnose, and that’s the worst disease . . . for dogwoods, so . . .”

Indeed it is the worst, as exotic, introduced diseases often are. It first began decimating native Cornus florida in the Northeast and C. nuttallii in the Northwest in the late 1970s ​[5, 7]​. It begins as leafspots, but kills entire leaves and moves down into shoots. It also infects shoots directly, causes stem cankers, and infects flowers. The kousa dogwood (Cornus kousa) is from east Asia and is generally resistant. This is a clue to the origin of the pathogen, Discula destructiva. Some hybrids between C. florida and C. kousa are also resistant ​[12]​, and resistance has been showing up in the native C. florida as well ​[4]​.

A subtle acting nugget is Harry’s line when inviting himself to the planting, “No, I’m serious. This is not a — it’s not any trouble at all.” It seems he was about to say he really wants to help plant the tree; it’s not a ploy to get more information from Jamie, but just caught himself.

Needle cast, fungicides, and other romantic talk

In S03E03, Ambrose casts a romantic spell with his talk of trees, their health and mitigating fungicides.

What’s the needle cast on Sonya’s blue spruce? Blue spruce (Picea pungens) is not native to eastern North America, but it is widely planted there. There are several needle rusts in the genus Chrysomyxa that infect blue spruce ​[6]​. They can cause foliage loss, but of course the diseases they cause are not needle casts.

There are a few true needle casts that can attack blue spruce, but they are unlikely. Lophodermium piceae causes a serious disease of spruce in Europe but, in America, it only infects senescent needles or under severe conditions. Lirula macrospora is a nice needle-cast pathogen of spruces, but either does not occur or is not common in the East.

The most common, widespread, and damaging foliage disease of spruce is caused by Rhizosphaera species, primarily R. kalkhoffii. The disease is often called Rhizosphaera needle cast, but it is a blight type-disease: sporulation occurs throughout the growing season ​[11]​ and at least some pathogen species have multiple generations per year ​[1]​. It definitely occurs in the East and can be severe on trees out of their native range ​[6, 11]​. If The Sinner writers included a disease they had actually experienced or heard about, this is almost certainly it.