Preliminary Nematode Survey from Soybean-Corn Rotations in the Mid South U.S.

Soybean is host to five main species of plant-parasitic nematodes (PPN) which are endemic in the mid-southern USA. These include soybean cyst nematode (SCN; Heterodera glycines), reniform nematode (RN; Rotylenchulus reniformis), root-knot nematode (RKN; Meloidogyne incognita), lance nematode (LN; Hoplolaimus columbus) and sting nematode (SN; Belonolaimus longicaudatus). Rotation with non-host crops is an effective management tool for soybean PPN. Rotation trials involving soybean, corn and milo are underway at seven sites in five mid-southern states of Arkansas (2 sites), Louisiana (1 site), Missouri (1 site), Mississippi (2 sites) and Texas (1 site). The objective is to assess the changes in nematode densities following different rotation combinations, irrigation schedules and residue management over a six-year rotation period. Soil samples were taken at the beginning of the trials from each treatment site and PPN were extracted from 200 cm³ by elutriation-sucrose centrifugation method. Nematode counts and species identification were made under a stereo microscope at x60 and densities were reported per pint of soil. Nematode indentification showed that the SCN, RN, lesion nematode (PN; Pratylenchus spp.) and RKN were present at the trial sites and were more abundant in the irrigated sites with soybean and burned residue, however, infestation densities differed between sites. The RN was most abundant, with the greatest densities of 1,342 RN pint^-1 of soil observed at the Stoneville, MS site, followed by the RKN (1,006 pint^-1 of soil) at the Portageville, MO site and at the Newport, AR site (670 RKN pint^-1 of soil) respectively. RKN was not detected at the Pine tree, AR, Brooksville, MS and Texas sites. The SCN was detected only in AR at a density of 336 SCN pint^-1 of soil, and occurred in a single soil sample obtained from the Pine tree site. The greatest densities of the PN of 186,818 pint^-1 of soil were detected at the St. Joseph site in LA and none was detected at the Brooksville, MS site. The lowest densities of all the nematode species were detected at the Brooksville, MS site. Densities as high as 4,694 pint^-1 of soil, of the ring nematode (Criconemoidesspp.) were detected only at the St. Joseph, LA site, whilst other species of minor economic importance including stunt, stubby, spiral and dagger nematodes were also detected at most of the trial sites.