CHANGES IN PLANT-PARASITIC NEMATODE POPULATIONS IN PINEAPPLE FIELDS FOLLOWING INTER-CYCLE COVER CROPS

The use of plant-covers oat (Avena sativa L.), rhodegrass (Chloris gay ana Kunth), soybean (Glycine max [L.] Merr.), and marigold (Tagetes pa tula L.) during pineapple inter-cycle planting periods was investigate d at two sites (Kunia and Whitmore, Oahu, III) as a potential means to reduce population densities of Rotylenchulus reniformis, Helicotylenc hus dihystera, and Paratylenchus spp. Clean fallow and follow covered with pineapple-plant resides (mulch) were the controls without plant-c over. Regardless of treatments, population densities of R. reniformis declined with time at both sites to low reside levels by the end of th e 6-month period. Treatment mens of R. reniformis population densities in the plant-cover treatments were lower than the controls (P = 0.05) . The plant-cover treatments also effected higher rates of R. reniform is population decline at both sites during the period, being 2.0 to 2. 2 times that of the mulch control and 1.2 to 1.4 times that of the fal low control. Plant-covers' effect on H. dihystera during the same peri od at both sites was variable, resulting in decreased, unchanged, or i ncreased population densities. The change was especially obvious in th e oat-cover treatment, where H. dihystera population densities increas ed 9 to 15-fold at both sites. Population of Paratylenchus spp, ws abs ent or present at low levels at the sites throughout the period. Biolo gical activities antagonistic to R. reniformis at Kunia were estimated at the end of 6 months by comparing the extent of nematode's reproduc tion (on cowpea seedlings) in the treatment soils that had been subjec ted to autoclaving or freezing temperature. Although higher indices of antagonistic activities were observed in soils with prior plant-cover treatments than in soils from the controls, none of the treatments re sulted in conferring soils the increased ability to suppress re-introd uced R. reniformis populations or enhance subsequent pineapple-plant g rowth.