EFFECT OF 1,3 DICHLOROPROPENE AND ROOTSTOCKS ALONE AND IN COMBINATION ON TYLENCHULUS SEMIPENETRANS AND CITRUS TREE GROWTH IN A REPLANT MANAGEMENT PROGRAM
The effects of 1,3 dichloropropene and rootstocks alone and in combination on Tylenchulus semipenetrans population densities and tree growth were evaluated during three years in a nematode-infested citrus orchard. The experiment was a 2 × 2 factorial with six replications. One factor was fumigation and the second, citrus nematode resistant and susceptible rootstocks. Soil population densities of the citrus nematode remained below detectable levels in fumigated plots planted with the resistant rootstock Cleopatra mandarin × Poncirus trifoliata 03.01.5 throughout the study. The nematode was not recovered from fumigated plots with Carrizo citrange until after the third year, when it appeared sporadically in some of the plots. The nematode was not recovered from citrus roots of either rootstock in fumigated plots. In non-fumigated plots, the resistant rootstock suppressed nematode reproduction. The number of juveniles per 250 cm3 soil, females per gram of root, and eggs per gram of root were 8, 6, and 0.3%, respectively, compared to Carrizo citrange by the third year. The trunk diameter of Orogrande mandarin scion was greater on the resistant than on the susceptible rootstock in non-fumigated plots, but there was no difference in fumigated plots. Fumigation with 1,3 D combined with the resistant rootstock 03.01.5 retarded nematode reinfestation for at least three years. Also, 1,3 D delayed reinfestation of the plots with the susceptible rootstock. The resistant rootstock suppressed nematode reproduction, and the growth rate of the nematode on this rootstock was slower than on the susceptible one.
