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What Are Fig Nematodes: How To Treat Figs With Root Knot Nematodes

What Are Fig Nematodes: How To Treat Figs With Root Knot Nematodes


By: Liz Baessler

Root knot nematodes are a serious problem associated with fig trees. Tiny little roundworms that live in the soil, these nematodes will cause noticeable stunting of the tree and lead to its eventual death. Keep reading to learn more about recognizing fig root knot nematode symptoms and how to manage figs with root knot nematodes.

What are Fig Nematodes and What Do They Do?

Nematodes are microscopic roundworms that live in the soil and feed on the roots of plants. While some nematodes are actually beneficial, there are many that damage or even kill the plants they infest.

There are several species of nematode that can infest fig roots, including dagger nematodes, lesion nematodes, and ring nematodes. By far the most common and the most dangerous, however, are root knot nematodes.

Fig Root Knot Nematode Symptoms

Root knot nematodes on fig trees live up to their name– they often show themselves with bumps or “knots” on the roots of the tree. Aboveground, the tree has a generally stunted and unhealthy look. It can be hard to diagnose the presence of root knot nematodes by sight alone, since the symptoms could mean any number of diseases.

In order to know for sure, you should take a sample of your soil and send it away for diagnostics. As the nematode infestation gets worse, it will create more bumps and galls on the roots. These galls inhibit the tree’s ability to take up nutrients and will eventually lead to the tree’s death.

How to Control Root Knot Nematodes on Fig Trees

There is no real cure for figs with root knot nematodes. Once an infestation takes hold, the best course of action is to fertilize vigorously. This will encourage root growth and hopefully give the tree enough uninfected roots with which to take in nutrients. Even this is just delaying the inevitable, however.

Prevention is the only real solution. Before planting, have your soil tested for root knot nematodes. Ideally, you should plant in a spot that is completely free of them. If you simply have to use a site that is infested, you can fumigate the soil before planting to lessen the infestation. Don’t fumigate soil you have already planted in, as it will likely kill the tree.

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Contents

  • 1 Etymology
  • 2 Taxonomy and systematics
    • 2.1 History
    • 2.2 Phylogeny
    • 2.3 Nematode systematics
  • 3 Anatomy
    • 3.1 Digestive system
    • 3.2 Excretory system
    • 3.3 Nervous system
  • 4 Reproduction
  • 5 Free-living species
  • 6 Parasitic species
    • 6.1 Agriculture and horticulture
  • 7 Epidemiology
  • 8 Soil ecosystems
  • 9 Society and culture
  • 10 See also
  • 11 References
  • 12 Further reading
  • 13 External links

The word nematode comes from the Modern Latin compound of nemat- "thread" (from Greek nema, genitive nematos "thread," from stem of nein "to spin" see needle) + -odes "like, of the nature of" (see -oid).


How Tables 2 and 3 were prepared

These tables combine and summarize the research efforts of several researchers over a number of years (McSorley 1994, McSorley and Frederick 1994, McSorley and Frederick 2001, Mendes et al. 2007, Om et al. 2008, Wang and McSorley 2005, Wang et al. 2004). In all of these studies, the researchers used similar methods, so it is possible to compare results among the different studies. An older study from the 1930s used different methods, and the identification of the root-knot nematode species was not clear at that time. Crow (2007) gives a good summary of this older study as well as some other work: http://edis.ifas.ufl.edu/in470.

In the studies used to prepare Tables 2 and 3, all researchers used a root gall index to rate the severity of root-knot infestation on the roots of a plant. Several studies also reported the number of nematode eggs produced per plant, and/or numbers of hatched mobile juveniles (J2) that were produced per plant. We wanted to develop a rating scale for flower cultivars that included root gall indices as well as the numbers of eggs or juveniles produced per plant. Ratings were assigned based on the categories shown in Table 1. A rating was given in each category (gall index, eggs per plant produced, and J2 per plant) for each species/race of nematode and each plant cultivar. In most cases, ratings were identical or similar in all categories, so the corresponding descriptive term was used in Tables 2 and 3. If ratings were close they were averaged, but if they were far apart, the result was described as “variable." If a nematode has not been tested on a particular cultivar, then the result is listed as “unknown."


Forest Pests: Insects, Diseases & Other Damage Agents

John L. Ruehle - Plant Pathologist, Southeastern Forest Experiment Station, USDA Forest Service, Athens, GA, and
Jerry W. Riffle - Plant Pathologist (retired), Rocky Mountain Forest and Range Experiment Station, USDA Forest Service, Lincoln, NE.

Cordell C.E., Anderson R.L., Hoffard W.H., Landis T.D., Smith R.S. Jr., Toko H.V., 1989. Forest Nursery Pests. USDA Forest Service, Agriculture Handbook No. 680, 184 pp.

Seedlings of all tree species are susceptible, at least to some degree, to plant-parasitic nematodes. The nematodes most damaging in forest nurseries include root-knot nematodes, Meloidogyne spp.: pine cystoid nematodes, Meloidodera spp. lance nematodes, Hoplolaimus spp. lesion nematodes, Pratylenchus spp. stunt nematodes, Tylenchorhynchus spp.: stubby-root nematodes, Trichodorus spp.: and dagger nematodes, Xiphinema spp. Some parasitic nematodes have a wide host range, feeding on many different forest tree species. Others have more restricted feeding habits.

Distribution

Plant-parasitic nematodes occur in forest nurseries throughout the United States. Because cool temperatures are unfavorable to most species, root-knot nematodes are not important parasites in the Northern States. Conversely, certain pathogenic species of lesion nematodes-effective pathogens in colder regions-are rarely found in southern nurseries.

Nematodes seldom kill seedlings outright. They may, however, severely debilitate the plant through partial destruction of the root system. Wounds caused by nematode attack may serve as points of entrance for root pathogens such as Fusarium spp. The resulting disease complex may then cause significant mortality.

Nematodes seldom kill seedlings outright. They may, however, severely debilitate the plant through partial destruction of the root system. Wounds caused by nematode attack may serve as points of entrance for root pathogens such as Fusarium spp. The resulting disease complex may then cause significant mortality.

Nematode diseases ordinarily cannot be diagnosed solely by their symptoms, which are indicative of a poorly functioning root system. Other parasitic organisms and certain environmental factors produce similar symptoms. The reaction of plants to attack by plant-parasitic nematodes varies considerably with the host-parasite combination.

Diseased seedlings are stunted (fig. 43-1), and their foliage is reduced in size and becomes chlorotic (fig. 43-2). They often show symptoms of nutrient deficiency, even when high levels of soil fertility are maintained. Affected plants lack vigor and usually cannot withstand extended periods of soil moisture stress.

Figure 43-1. - Pine seedling on right was severely stunted by nematode attacks.

Figure 43-2. - Chlorotic pine seedlings in beds heavily infested by nematodes. Beds at far left were fumigated with methyl bromide.

Figure 43-3. - Slash pine seedlings (1-0) lifted from a Florida nursery show galls on their taproots caused by root-knot nematodes (Meloidogyne spp.).

The underground root symptoms vary with the nematode species. Root-knot nematodes may cause galls on the roots (fig. 43-3) and, roots near the galls. On certain hosts, dagger nematodes cause galls and bending of lateral roots. Pine cystoid nematodes cause few, if any, galls and are visible only when the swollen females erupt through the roof epidermis. In contrast, lesion nematodes cause a necrosis of the cortex, which results in a general decay of the feeder roots. The lance nematode- an internal parasite particularly damaging to pine seedlings-also migrates through the cortical tissue and causes extensive internal cell destruction, which allows other pathogens to enter and further damage the root system.

Nematodes that do not enter the roots generally have less obvious effects on free seedlings. Stunt, stubby-root, and dagger nematodes cause discoloration and surface lesions. The most frequent effect of their feeding is a general stunting of lateral roots without noticeable decay.

Nematodes are submicroscopic, slender, white worms. Specialized laboratory equipment is required to extract them from plants and soils. Identification to genus and species usually requires the services of a nematologist.

All plant-parasitic nematodes have a stylet at their anterior end. They use this sharp-pointed tube to puncture plant cells and remove cellular contents. Some species feed internally in the feeder roots: others remain at the root surface and feed externally.

These feeding wounds provide entry points for other pathogens. The resulting disease complex may destroy more seedlings than a single pathogen acting alone.

Cultural - Crop rotation controls certain nematodes. In the rotation sequence, favor crops that are not susceptible. For example, where root-knot nematodes are a problem, rotation with fescue, a non-host, is recommended over soybeans, a host.

Chemical - Fumigate the soil before seeding to control nematodes in forest nurseries. Methyl bromide is one of the most effective soil fumigants and provides excellent control in most nurseries. When nematodes are a problem in isolated nursery sections, spot injection with less volatile nematicides provides satisfactory control.

Dip roots of infected hardwoods in chemical solutions to control root-knot nematodes. A 15-minute dip in fensulfothion has been effective in protecting catalpa and dogwood. Immersing bare roots in hot water at 126 0F for 2 minutes has controlled lesion nematodes infecting eastern redcedar.

Selected References

Peterson, Glenn W. 1962. Root lesion nematode infestation and control in a plains forest tree nursery. Res. Note 75. Fort Collins, CO : U. S. Department of Agriculture. Forest Service. Rocky Mountain Forest and Range Experiment Station. 2 p.

Ruehle, John L. 1975. Nematodes. In: Peterson, Glenn W. Smith, Richard S., Jr., tech. Cords. Forest nursery diseases in the United States. Agric. Handb. 470 Washington, DC: U.S. Department of Agriculture: 31-34.

Ruehle, John F. 1973. Nematodes and forest trees - types of damage to tree roots. Annual Review of Phytopathology. 11: 99-118.


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