Variability in Time and Space of Meloidogyne incognita Fall Population Density in Cotton Fields

Terry A. Wheeler, Brant Baugh, Harold Kaufman, Greta Schuster, Kerry Siders

Abstract


Three cotton fields infested with Meloidogyne incognita were intensively sampled in the fall for 3 years (1996 to 1998) to determine if intensive sampling for M. incognita, for which spatial location is important, was necessary every year in a continuous cotton system. Two composite soil samples (20 cores each), taken over an area covering one-third of the field length and two rows wide, were averaged to represent that area (row-location combination). Each field (except one) had 24 areas assayed for changes in M. incognita population density (Pf) over a 3-year period. At all three sites, Pf was higher during fall 1998 than fall 1996. There were no differences in Pf between rows within a year or between years (no. row × year interaction) at any of the sites. At all three sites, there was a consistent difference each year in Pf among locations in a field (no. year × location interaction). At each area, M. incognital/500 cm³ was labeled for one of four Pf classes: 250, 250 to 999, 1,000 to 2,499, and = $2,500. Management of root-knot nematode would likely be altered as classification changed. The areas that were reclassified by two classes or more after 1 and 2 years ranged from 0 to 29% and 25 to 54%, respectively. The risk of underestimating Pf of M. incognita was higher in one site 2 years after the initial intensive sampling procedure, whereas in another site there was little change in Pf 2 years after initial sampling. Sampling frequency will need to be decided on a field-by-field basis.

Keywords


cotton; meloidogyne incognita; nematode; population dynamics; root-knot nematode; sampling; spatial variability; temporal variability

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