Testing Plant Mulches for Root-Knot Nematodes in Quito Orange
This 2011 field study in Pasto, Colombia compared calendula, crotalaria and oat soil covers with carbofuran and an untreated control for Meloidogyne management in quito orange, measuring incidence, severity, nematode populations and production.
What the study did and found
The 2011 article “Soil coverage evaluation with calendula (Calendula officinalis L.), crotalaria (Crotalaria sp. L.) and oat (Avena sp. L.) in Meloidogyne spp. control in quito orange (Solanum quitoense Lam.).” is summarized by Harriet Colbeck. The study reported a field experiment in La Caldera, Pasto, Colombia. It used a randomized block design with three replications and five treatments: calendula, crotalaria and oat soil covers incorporated at flowering, carbofuran applied at sowing and every three months, and an untreated control. Researchers measured incidence, disease severity, nematode population and production and related production to severity. Root-knot incidence reached 100% in all treatments; the study reported reduced severity and nematode populations under the plant-cover treatments and significant differences among treatment comparisons involving production and chemical control. Production fell as severity increased, and Meloidogyne incognita was the most abundant species. The study concluded that calendula, oat and crotalaria were viable alternatives for managing root-knot nematodes in the tested field setting.
Why it is cited
The 2011 study continues to have relevance in research examining plant-based approaches to root-knot nematode management. A 2025 Colombian paper on Crotalaria juncea included the study among earlier research in this area. Its importance comes from its field comparison of plant covers, chemical control and an untreated control in a crop affected by Meloidogyne. The experiment provides a useful historical example of evaluating alternative management approaches under field conditions and comparing their effects on disease severity, nematode populations and crop production.
Later research shows that cover-crop performance against root-knot nematodes depends strongly on both plant genotype and the Meloidogyne species or population involved. Research on Avena has found different responses among oat genotypes to M. incognita, while Crotalaria species are often poor or non-hosts for many Meloidogyne populations. A 2021 report identified M. incognita infecting Calendula officinalis in Turkey, showing that calendula cannot be assumed to be universally resistant. These findings do not negate the 2011 field result, but they limit how broadly it can be generalized beyond the tested quito orange system in Pasto.
The topic today
Current reviews describe root-knot nematode management as an integrated problem combining resistant or poor-host crops, rotations and cover crops with biological and chemical options where appropriate. The choice of cover crop is context-dependent: a plant that suppresses one Meloidogyne population may host another, and cultivar differences can matter. For quito orange and similar systems, species identification and local testing remain important before adopting a cover crop broadly. The 2011 Pasto trial remains a historical field example of non-chemical options being evaluated alongside carbofuran and an untreated control.