Phytomyxea

Phytomyxea molds cause important diseases, including club root in cabbage and its relatives, and powdery scab in potatoes.

Oomycetes

The oomycetes are not true fungi but are fungus-like organisms. They include some of the most destructive plant pathogens including the genus Phytophthora, which includes the causal agents of potato late blight  and sudden oak death.

Nematodes

Nematodes are small, multicellular wormlike animals. Many live freely in the soil, but there are some species that parasitize plant roots. They are a problem in tropical and subtropical regions of the world, where they may infect crops.

Zoospores

Zoospores that are very durable, and may be able to survive in a resting state in the soil for many years. They have also been shown to transmit plant viruses.

Toxins

These can be non-host-specific, which damage all plants, or host-specific, which cause damage only on a host plant.

Necrotrophic fungi

Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells.