Lavender and Nematodes
Answered by: Conrad Richter
Question from: Edward Howell
Posted on: September 30, 2006

I’ve read somewhere that nematodes are not good for lavender plants. Since there are over 20,000 different types of nematodes, are there any types of nematodes that will work with lavender?

Of 10,000 species of nematodes that have been described some 2,500 are considered pests to plants. At least some of the rest are actually beneficial to plants; for example, Richters sells a beneficial nematode product called Scanmask that attacks soil-borne insect pests such as grubs and fungus gnat larvae. For a good introductory overview of nematodes see Ingham and Jensen’s article, "Nematodes" (http://plant-disease.ippc.orst.edu/articles.cfm?article_id=1).

Nematodes specialize on certain host plants. For example, /Pratylenchus penetrans/ attacks apple roots, /Pratylenchus neglectus/ attacks potato roots, and /Xiphinema americanum/ attacks grape roots. /Meloidogyne hapla/, /M. //incognita/ and other Meloidogyne species are known to attack lavenders and other herbs, causing deformed roots called "root-knots" and distorted or stunted above-ground growth.

Marigolds produce an exudate that is lethal to many root-knot nematodes including Meloidogyne incognita and M. javanica. Mexican marigold (Tagetes minuta) is the best species. It is possible to grow marigolds -- even the common french or african types -- to clear an area of nematodes before planting herbs such as lavender. For directions see http://www.ncagr.com/agronomi/nnote1.htm.

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