Fungi and the Decrease of Cereal Cyst‐nematode Populations in Cereal Monoculture 1

Populations of the cereal cyst‐nematode decrease when cereals are grown frequently or continuously because the females that develop on the roots between May and July fail to produce eggs, or produce a smaller number than expected. Consequently, cysts in the soil after harvest are fewer and contain fewer eggs. The role of fungal parasites and competitors in limiting populations of cyst‐nematodes is reviewed. Parasites of eggs and females of Heterodera avenae Woll. were widespread in British cereal fields, an Entomophthora‐like fungus and Verticillium chlamydosporium Barron & Onions being the most common species found. Although fungal parasites may be the cause of the failure of the nematode to increase, it has not yet been established unequivocally.