Root feeding by ectoparasites, such as the spiral (Helicotylenchus spp.), stubby-root (Paratrichodorus spp.), and stunt nematodes (Tylenchorhynchus spp.), causes root stunting and pruning that can restrict root penetration in soil (Fig. 10-1). Endoparasites, such as lesion (Pratylenchus spp.) and root-knot (Meloidogyne spp.) nematodes result in necrotic lesions and galling that impair root function (Fig. 10-2 and 10-3). Nematodes tend to cause greater plant damage in sandy soils because these soils are conducive to nematode activity and to drought stress.


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Fig. 10-1. Left: The lance nematode (Hoplolaimus spp.) may feed on the outside of the root, embedding only its head, or it may completely enter the root to feed (photo: R.F. Davis). Right: Roots damaged by lance, sting, and stubby-root nematodes are restricted in their growth and may have necrotic lesions (photo: N.A. Minton).


Fig. 10-2. Left: The lesion nematode (Pratylenchus spp.) spends most of its life within the root where it feeds on cells in the cortex (photo: U. Zunke). Right: Feeding and migration of lesion nematodes within the roots result in necrotic lesions and reduced root efficiency (photo: A. France).


Fig. 10-3. Left: Roots galled by root-knot nematodes (Meloidogyne spp.) (photo: G. Caubel). Right: Stained root-knot nematode showing swollen female feeding in vascular system and egg mass protruding from the gall (arrow) (photo: W.F. Mai).


Hoveland et al. (1975) observed that the roots of two tall fescue cultivars were shallower in a sandy soil infested with the lance (Hoplolaimus spp.), stunt, and stubby-root nematodes than in the same soil treated with a nematicide (carbofuran, 2,3-dihydro-2,2-dimethyl-7-benzofuranylmethylcarbamate) or a broad-spectrum fumigant (methyl bromide). They speculated that root pruning by the nematodes led to greater stand loss during periods of drought. Moreover, forage yields in the second year of production were reduced by 28 and 52% in untreated plots compared to plots treated with the nematicide and fumigant, respectively.

In greenhouse pots, single species infestations of lance, stubby-root, or pin nematode (Paratylenchus spp.) reduced top weight of ‘Kentucky 31' (KY-31) tall fescue over that of noninfested controls (McGlohon et al., 1961). The lance and stubby-root nematodes also reduced root weight. In another greenhouse experiment, forage yields of ‘Kentucky 45-50' tall fescue were reduced by the lesion nematode (P. scribneri) when compared with noninoculated controls (Minton, 1965).


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