Methyl bromide is an effective pre-plant soil fumigant used to control nematodes in many high-input, high-value crops in the United States, including vegetables, nursery plants, ornamentals, tree fruits, strawberries, and grapes. Because methyl bromide has provided a reliable return on investment for nematode control, many of these commodities have standardized their production practices based on the use of this chemical and will be negatively impacted if effective and economical alternatives are not identified. Alternative control measures based on other chemicals, genetic resistance, and cultural practices require a greater knowledge of nematode biology to achieve satisfactory results. Here, we provide an overview of nematode management practices that we believe will be relied upon heavily in U.S. high-value crop production systems in a world without methyl bromide. Included are case studies of U.S. high-value crop production systems to demonstrate how nematode management practices other than methyl bromide may be incorporated.

Descriptions and selected redescriptions of the 98 putative species in the genus Longidorus Micoletzky, 1922 were reviewed for information on the occurrence of juvenile stages (=developmental forms). For 43 of the 98 species information on juvenile forms was not available, two species had only the J4 stage described, four species had only the J3 and J4 stages described, for ten species data were provided for three juvenile stages and four juvenile stages were described for 39 species. However, the published morphometrics for numerous species do not allow an unequivocal determination to be made of the developmental stage(s) as described by the authors. In the description of L. jonesi only three groups of juvenile stages were identified and subsequently populations of L. martini and L. taniwha were also reported with only three juvenile stages and not four as is usual for the Nematoda. Populations of L. diadecturus, L. pisi and L. taniwha, each species having a posteriorly located guide ring, were examined. Data are presented which demonstrate that, as with L. martini, L. pisi and L. taniwha, each have only three juvenile stages, whereas L. diadecturus has four such stages. The shift from four to three juvenile stages is considered to be a derived state which may be a result of hormonally mediated heterochrony, possibly expressed as a single gene change. It is proposed that species unequivocally demonstrated to have only three juvenile stages, the terminology should be JI, JII and JIII, whereas for all other species the existing terminology should be used, J1, J2, J3 and J4.

Cyclic hydroxamic acids are secondary metabolites found in the family Poaceae and have been implicated in the allelopathy of rye (Secale cereale). The toxicity of these compounds against plant-parasitic nematodes is unknown. DIBOA (2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one), DIMBOA (2,4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one), and their degradation products BOA (benzoxazolin-2(3H)-one) and MBOA (6-methoxy-benzoxazolin-2(3H)-one) were screened in vitro against Meloidogyne incognita second-stage juveniles (J2) and eggs and mixed-stages of Xiphinema americanum. Xiphinema americanum was more sensitive to DIBOA and DIMBOA than M. incognita J2, with a maximum apparent mortality of 96 and 92% compared to 73 and 72% at 90 mug/ml. Eggs of M. incognita were less sensitive to the hydroxamic acids than J2; only DIBOA resulted in a 50% reduction in egg hatch, with a lethal concentration (LC(50)) of 74 mug/ml compared to 21 mug/ml for J2. When M. incognita J2 were exposed to DIBOA for 48 h and the compound was removed and replaced with water, the LC(50) value increased from 21.0 to 40.7 mug/ml. MBOA was not toxic to X. americanum or M. incognita eggs, but was toxic to M. incognita J2, with LC(50) values of 44 and 20 mug/ml before and after the compound was removed and replaced with water. BOA was the least toxic hydroxamic acid tested; it did not reduce M. incognita egg hatch after 1 week of exposure or increase X. americanum mortality after 24 h of exposure. While in vitro studies provide a valuable starting point in determining the toxicity of the chemical component of rye, the relevance of the data to soil remains to be determined.

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