FAQs

Fungal/Root Feeding Nematodes

What are fungal/root feeders?

On the main page of your Soil Foodweb report, when you have nematodes assessed, we report the total nematode number per gram dry weight of soil. On the third page of the report will be a list of how many individuals of each functional group and genus are present per gram of fresh soil. Bacterial Feeders, Fungal Feeders, Predators and Root Feeders are self-explanatory, but what are Fungal/Root Feeders, also referred to as switchers*? How concerned should you be about their presence?

Switchers are a group of genera, all belonging to the large order Tylenchida (the same order which contains most of the plant-parasitic nematodes) whose feeding habits, with a few noteworthy exceptions, are not that well understood. Most of them seem to feed primarily upon fungi, but may feed occasionally upon the growing roots of green plants if insufficient fungi are present in their environment. Some tend to be found regularly in association with particular plants, and may in fact be feeding upon the mycorrhizal fungi associated with those plants. Aphelenchus species are often found in roots infected with parasitic fungal species such as Pythium, but not in healthy roots, and they appear to be feeding upon the fungal pathogen rather than the plant itself. This could in fact be a very positive interaction from a plant viewpoint.

The few species that are known to cause significant crop damage occur in the genera Aphelenchoides (Foliar nematodes), Ditylenchus (Stem and Bulb nematodes), Bursaphelenchus (Pine Wilt nematode) and Rhadinaphelenchus (Red Ring nematode). The latter two genera never occur in the soil, as they spend their entire life cycle within the host plant or in the pores of the vector insect that transmits them to new hosts.

The most damaging Aphelenchoides species include A. besseyi which causes white tip of rice, strawberry and African violet; A. fragariae which causes bunchy top and blasting of blossoms in flax, mint, onion, oat, sweet potato, begonia, fern, iris and lily; and A. ritzemabosi which harms strawberry, white clover, orchid, violet and chrysanthemum. These species can overwinter in fallen leaves of the host plants, becoming active in the Spring to infest new hosts. They can propagate rapidly in greenhouses. Careful sanitation, including use of compost or compost tea with adequate competitors, are probably the best control methods for these problems.

Harmful Ditylenchus species include D. dipsaci, which causes white flagging of alfalfa , clover, and strawberry and bulb bloat in onion, garlic, and some flowers; and D. destructor, the Potato Rot nematode. D. myceliophagus is a fungal feeder which has become a pest in commercial mushroom growing operations. These species are persistent pests and again best controlled by bringing competitor species into the soil.

But it is important to remember that both of these are large genera, and only a few species within each are known to damage crops. The rest of the 138 species of Aphelenchoides, and 86 species of Ditylenchus, probably graze on fungi. Aphelenchoides composticola is a fungal feeder which, as the name implies, is commonly found in compost. So when Aphelenchoides turn up in your compost, if it is otherwise good compost, this is not cause for undue alarm: you probably have a harmless or beneficial species.

The best way to deal with any of these switchers is to make sure adequate fungi are present. That gives the beneficial or neutral species food to do their jobs, or adds the competitors to compete with and reduce the number of pests.