Photographer: Sandra Jensen, Cornell University Source: Bugwood.org Copyright: CC BY-NC 3.0 US
Photographer: Bruce Watt, University of Maine Source: Bugwood.org Copyright: CC BY-NC 3.0 US
The genus Ditylenchus is an extensive one containing 81 species, and within the species Ditylenchus dipsaci there are 30 races (variations). The races are not physically different in appearance but have different developmental requirements. Overall, both sexes of the nematode range from 1-2 mm.
It is a migratory endoparasite, which means it live within plant hosts and can migrate within the host, or to other hosts. Symptoms of infestation increase with the number of nematodes. In garlic, leaves become yellow and die, while the scales on the bulbs loosen and break. In onions the leaves start to curl.
This nematode is one of the more destructive pests of several economically important crops such as alfalfa, garlic, onion, and tulips. Alfalfa is a crop of striking economic importance due to its usage as forage in the farming and ranching industry. Over 61 million tons of alfalfa were harvested in 2014, earning billions of dollars in revenue for the United States. This pest has been observed to also infect tulip leaves and stems, peas, beetroots, pumpkin and rhubarb, and 450 more plant species. By having a wide breadth of potential hosts, resistance to desiccation, and the persistence of the detrimental parasite is inevitable.
Sexually reproducing individuals take 19-23 days to complete their lifecycle. They survive up to 75 days and each female produces 200-500 eggs. Six generations can happen in one year. After hatching, the larvae go through several juvenile molts. All life cycle phases are infective, and enter plants through wounds or the stoma. They release enzymes that soften the cell walls, allowing them to feed easier while causing damage to the plant. The fourth juvenile molt is the hardiest, and can survive desiccation.
First discovered in the northwestern United States in the 1920s, it has spread throughout states with high alfalfa production such as California, Idaho and Montana. By 1940 it was found in New York, and has now be confirmed in 25 states and D.C.
Originally described by Friedrich Kuhn in 1857 in Germany. Re-described by Ivan Filipjev.
U.S. Habitat: Anywhere potential hosts are present, especially alfalfa, garlic and onion.
U.S. Present: AZ, CA, CO, DC, DE, ID, KS, MA, MD, NC, NH, NJ, NM, NV, NY, OK, OR, PA, SC, TN, TX, UT, VT, WA, WV, WY
Other Ditylenchus species.
Rotations of wheat, barley and other non-host crops are recommended for 3 or more years on infested land. Also, any potential weeds (ryegrass, toadflax) that can sustain nematode populations must be maintained. Other management practices suggested are seed and bulb sanitation by hot water treatments, fumigation of fields with chemicals specific to Ditylenchus species, and cleaning of agricultural equipment. Fumigants should be applied after emergence, but before planting.
Ellenby, C. 1968. Desiccation survival in the plant parasitic nematodes, Heterodera rostochiensis Wollenweber and Ditylenchus dipsaci (Kuhn) Filipjev. Proceedings of the Royal Society of London B: Biological Sciences, 169(1015), 203-213.
Godfrey, G. H. 1923. The Eelworm Disease; a Menace to Alfalfa in America. United States Department of Agriculture.
Hafez, S. L., Golden, A. M., Rashid, F., & Handoo, Z. 1992. Plant-parasitic nematodes associated with crops in Idaho and eastern Oregon. Nematropica, 22(2), 193-204.
Jones, J. T., Haegeman, A., Danchin, E. G., Gaur, H. S., Helder, J., Jones, M. G., ... & Perry, R. N. 2013. Top 10 plant‐parasitic nematodes in molecular plant pathology. Molecular Plant Pathology, 14(9), 946-961.
Jordan, S. 2015. Managing The Spread of Alfalfa Stem Nematodes (Ditylenchus dipsaci): The Relationship Between Crop Rotation Periods and Pest Re-emergence.