Rotylenchulus reniformis below Plow Depth Suppresses Cotton Yield and Root Growth

Damage to cotton by Rotylenchulus reniformis below plow depth was evaluated in a sandy clay loam soil at Weslaco, Texas. In December 1999, 14 holes on 51-cm centers were dug 91 cm deep along the planting bed and adjacent furrow and 2 ml of 1,3-dichloropropene was placed 91, 61, and 30 cm deep as each hole was refilled and packed. This technique eliminated 96%, 81%, and 74% of R. reniformis down to 107 cm at distances 0, 25, and 51 cm laterally from the point of application (P </= 0.05), whereas chisel fumigation at 168 liters/ha 43 cm deep reduced nematode numbers only in the top 61 cm (P </= 0.001). Manual placement of fumigant increased yield 92%; chisel fumigation increased yield 88% (P </= 0.005). A second experiment in February 2001 placed fumigant 43 or 81 cm deep, or at both 43 and 81 cm. Holes alone had no significant effect on nematode density at planting, midseason or harvest, on root length density at midseason, or on cotton lint yield. Fumigant at 43 cm reduced nematode numbers above fumigant application depth at planting 94% (P </= 0.02), at midseason 37% (P </= 0.09), and at harvest 0%, increasing yield 57% (P </= 0.002). Fumigant at 81 cm reduced nematode numbers above fumigant application depth at planting 86% (P </= 0.02), at midseason 74% (P </= 0.02), and at harvest 48% (P </= 0.01), increasing yield 53% (P </= 0.002). Fumigating at both 43 and 81 cm reduced nematode numbers above 90 cm 94% at planting and 79% at midseason, increased midseason root-length density 14-fold below 76 cm, and doubled yield (P </= 0.02 in all cases).