| Popis: |
A randomized complete block experiment with 10 single-tree replicates and 7 treatments was conducted in a field of mature “Old Line Washington” navel orange trees in Field 63 at the University of California Lindcove Field Station, Exeter, California. Each experimental tree was surrounded on all 4 sides by untreated border trees. Trees were assigned to 10 blocks of 7 trees each based on their pre-treatment infestation level of CRS, so that the 7 trees within each block had similar pre-treatment infestations of CRS. Each of the 7 trees in each block then was assigned randomly to a treatment so that each treatment was represented once in every block. Six treatments were different application dates for Lorsban 4E at a dilution of 3/4 pt/100 gal. It was our original intention to apply all treatments in an identical manner, but our spray rig broke down half way through the experiment, and we had to use an alternate spray rig which was probably less effective than the first rig for obtaining good spray coverage. For this reason, results were compared only among treatments that were applied with the same spray rig. Applications by spray rig #1 were made at 460°520 psi and ca. 17-18 gal/tree and were applied with hand-held spray guns from both ground and tower (ca. 15-20 ft up) positions. Applications by spray rig #2 were made at 470 psi at ca. 19 gal/tree and were applied by hand-held spray guns from the ground only. The seventh treatment was an untreated control. The level of infestation of red scale in the plots was assessed once pre-treatment (Mar-Apr) and twice post-treatment (Dec, Mar 1989). In all 3 evaluations, 75 twigs (ca. 1-2 yr old, ca. 9 inch long)/tree were examined in situ and scored for the presence/absence of live CRS (only adult females were counted in the post-treatment evaluations while any stage except first instar was counted in the pre-treatment evaluation). In both post-treatment evaluations, up to 100 fruit/tree (100 were not always available, averages were 75 and 87 fruit/tree in the first and second post-treatment counts, respectively), were scored in situ as being infested with 0, 1°10, or >10 live or dead CRS (any stage). Infested fruit were categorized into those with more or less than 10 CRS/fruit because fruit generally are downgraded in the packinghouse when infested with approximately 10 or more scale. Also, both live and dead CRS are included in fruit evaluations because scaly fruit are downgraded in the packinghouse regardless of whether the scale are live or dead. Therefore, counts of live and dead CRS on fruit were used to assess how well a treatment protected the fruit from becoming infested and downgraded while counts of live CRS on twigs were used to assess how well a treatment suppressed population growth. During the 3.5 month period that encompassed all the application dates, red scale phenology was monitored weekly with pheromone traps and crawler traps. |
