Nematodes cause corky root disease; they can also prevent it, Aphelenchoides
By Gregory Jackson
Co-Founder of Groundz
(Photo: A fossilized nematode called Eophasma jurasicum, now extinct, by Ghedoghedo)
On September 13, Groundz ran our first compost test sample to learn that recently elevated ciliate levels had led to anaerobic conditions, which may not be healthy for farming or organic landscaping. While the first results indicated good nematode numbers, 27.8 per gram, it was not diverse.
In our second compost sample the nematode number had dropped to 22.5 per gram (still good according to the earthfort results), but also much more diverse. In the first compost sample tested, we found that of the 27.8 nematodes per gram, 27.8 wereRhabditidae sp. under the Bacterial Feeders category. In the second compost sample tested, we found that of the 22.5 nematodes per gram, not only are there five Bacterial Feeder species, but also a species of Fungal/Root Feeders, and a species of Predatory.
In particular, under the Fungal/Root Feeders, Aphelenchoides was observed in the sample. Aphelenchoides was researched in its application to fight corky root disease. Such compost acts as a pathogen suppression by competing (eating other nematodes that cause the disease and other crop-related diseases). Further, Fungal/Root Feeders that are pathogen-specific nematodes cannot always be expected in early stages of compost (“Effects of fungivorous nematodes on corky root disease of tomato grown in compost-amended soil” by M.K. Hasna, J. Lagerlof, & B. Ramert for the Department of Crop Production Ecology, and Swedish University of Agricultural Sciences, Alnarp, Sweden. 2008; 58:145-153).
In that study the authors investigated the effects of crops grown with compost, used to build up the health of food crops to help prevent corky root disease, by usingAphelenchoides.
The results revealed that Aphelenchoides need the right condition to reduce or prevent corky root disease. There was a significant relationship betweenAphelenchoides and cover crops (also known as “green manure“). While cover crops provide cover for the soil, creating tilth, and fixating atmospheric nitrogen into the soil (like peas), they compete with Aphelenchoides ability to feed on Xiphinema bakeri, which causes corky disease. Green manure alone had no affect on corky root disease. However, Aphelenchoides applied directly into the soil significantly reduced symptoms, in some cases alleviating the disease. Our sample has 0.58Aphelenchoides per milliliter. In the study, the author also noted that their numbers were also low in all experiments, which means just their presence in the compost indicates a healthy microbial diversity.
Another observable benefit of Aphelenchoides is they help establish and maintain mycorrhizal associations, according to M.W. Allen a researcher at University of UC Davis. Since Aphelenchoides is known to eat certain fungi, these interactions have been observed to encourage mycorrhizal root growth to help establish healthy plants.