| Host genus | Fungal species | Symptoms and notes |
| Juglans | Ophiognomonia leptostyla | Causes leaf spots |
| Pseudomicrostroma juglandis | White rust-like lesions on living leaves | |
| Juncus | Lichenopeltella sp. P2647 | Assumed to be a parasite due to presence of hyphopodia, but nutritional status unknown |
| Puccinia cancellata | Rust of stems/leaves | |
| Juniperus | Colpoma juniperi | Sometimes causes minor canker-like symptoms on bark |
| Lophodermium juniperinum | May fruit on moribund leaves, but does not appear to be a significant pathogen |