The year of the dagger nematode?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.     

The Chinese calendar depicts 12 animals; this is the year of the ox. The calendar shows, a bird (rooster), two reptiles (dragon and snake) and nine mammals. Nematodes, as well as all invertebrates, were excluded. However, based on the results of soil samples submitted to date to Diagnostic Services, 2009 may be the year of the dagger nematode.

Dagger nematodes are common plant-parasitic nematodes found in Michigan. One species is dominant in our state, Xiphinema americanum, but a second species exists on roses grown in glasshouses, X. diversicaudatum. Our most common species has a wide host range and will parasitize field crops (corn and soybeans), fruit (virtually all species are hosts) landscape plants (conifers, grasses, woody shrubs and trees), turf and vegetables (sweet corn). Many weeds also serve as hosts. They tend to prefer well-drained, sandy soils. They feed as ectoparasites (their bodies remain in the soil and only their stylets penetrate the roots). Primary symptoms are root death and a proliferation of small club-shaped lateral roots emerging behind the root cap. As mentioned, they are pathogens of many plant species, but they are most notorious for their spread of plant viruses such as tobacco and tomato ringspot viruses and peach rosette mosaic virus.

Dagger nematodes can survive for over a year in the soil as adults. Compared to many other species of plant-parasitic nematodes, they have long life cycles but fortunately do not produce large numbers of eggs (less than 50). As a special note, viruses are not passed through eggs to the juvenile nematodes. Viruses are acquired by feeding upon hosts that harbor them.

Typically, fewer than 100 dagger nematodes are recovered from soil samples (100 cm3 soil) submitted to the lab. However, a sample collected from young conifers at one Michigan nursery this spring contained 495 daggers. Other samples submitted from agricultural sites in the state have contained high population densities of these nematodes. It occurred to us we seem to be seeing higher numbers of dagger nematodes than usual.

You’re probably curious by now as to why this seems to be such a good year for dagger nematodes. We’re not really even sure we can provide the definitive answer. Daggers behave somewhat like needle nematodes as they prefer cool, moist soils. Both these nematodes feed on roots in the spring, but as soils become warm and dry during the summer months, they migrate deeper into the soil where they find conditions more favorable. They return to the root zones of their hosts in the fall, although with certain plants, such as grapes and tree fruits, they can remain deeper in the soil and still have roots to parasitize. Our opinion is the conditions we’ve experienced in Michigan from the fall of 2008 to this spring have really favored the survival and fecundity of dagger nematodes. The same is also probably true for needle nematodes, but they are generally not encountered as frequently as daggers.

Fruit growers (small and tree fruit) and nurserymen should monitor dagger nematodes very closely. Higher numbers of dagger nematodes increase the potential for the spread of viruses and it is typically the viruses, as opposed to the actual feeding by the nematodes that produce the most severe symptoms. Stone fruit orchards and vineyards, in particular, should be monitored for virus symptoms.

Growers of strawberries and field corn should be diligent about their monitoring for needle nematodes. These nematodes can also vector viruses, but needles are very destructive as their feeding can result in significant yield losses. Losses in corn, for instance, due to the corn needle nematode can be greater than 50 bushels/A.

The optimal time to sample for these nematodes is the spring and fall. Soil should be collected around the roots of their hosts and placed in plastic bags. Samples can be submitted to Diagnostic Services on campus. Please consult our web site for a submittal form and other pertinent information. There is a $25 fee for a nematode analysis. If high population densities of dagger or needle nematodes are recovered from a sample, management recommendations will be provided.

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