Earthworms are known as farmers’ best friends because of the multitude of services they provide that improve soil health and consequently plant health. The density of earthworms in the soil is considered to be a good indicator of a healthy soil because they improve many soil attributes like structure, water holding capacity, moisture content etc., and also increase nutrient availability and degrade pesticide residues. As scientists understand these ‘ecosystem services’ provided by earthworms, they discover that this earthworm-farmer friendship is a lot deeper than previously imagined!
The soil, in addition to being the habitat for crops, also nurtures other organisms, some of which can cause devastating diseases to plants. Research indicates that earthworm-composted organic matter, also called vermicompost, has disease suppressive properties. Elmer, in 2009 published findings that earthworms suppress soil-borne diseases in different vegetables by nearly 50-70 % and attributed this to the ability of earthworms to increase the activity of beneficial microorganisms. Wolfarth et al., further studied an earthworm species, Lumbricus terrestris, that preferentially incorporates Fusarium-infected wheat straw into the soil. Fusarium spp. causes a disease called Fusarium Head Blight on wheat that in addition to direct yield losses produces a mycotoxin called deoxynivalenol (DON), toxic to humans and animals. The researchers found that this particular earthworm reduces the fungal biomass and DON concentration in infected wheat straw, a finding particularly useful in minimally tilled wheat fields where the infected straw can remain on the soil surface for a long time. Thus, as it turns out, these farmers’ friends can directly reduce disease outbreaks by reducing the source of the disease i.e., infected crop residue.
Agricultural practices like tillage and pesticide use are known to adversely affect earthworm populations in the soil. These findings reinforce the importance of better appreciating the delicate inter-relatedness in an agricultural ecosystem while trying to develop crop management strategies.
Wade H. Elmer (2009). Influence of Earthworm Activity on Soil Microbes and Soilborne Diseases of Vegetables Plant Disease DOI: 10.1094/PDIS-93-2-0175
Friederike Wolfartha, Stefan Schradera, Elisabeth Oldenburgb, Joachim Weinertc, & Joachim Brunotted (2011). Earthworms promote the reduction of Fusarium biomass and deoxynivalenol content in wheat straw under field conditions Soil Biology and Biochemistry DOI: 10.1016/j.soilbio.2011.05.002