Timing Lorsban Applications for Crs Control, 1987

A randomized complete block experiment with 10 single-tree replicates and 11 treatments was conducted in a field of mature navel orange trees (2 varieties of navels were in the field: “Old Line Washington” and “Fisher”) in Field 63 at the University of California’s 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 11 trees each based on their pre-treatment infestation level of CRS, so that the 11 trees within each block had similar pre-treatment infestations of CRS. Each of the 11 trees in each block then was assigned randomly to a treatment so that each treatment was represented once in every block. Eight of the 11 treatments were different application dates for otherwise identical applications of Lorsban 4E (3/4 pt/100 gal) applied by, hand-held spray guns from both ground and tower positions at ca 500 psi and ca 17-19 gal/tree. Three of the 11 treatments were different application dates for otherwise identical applications of Lorsban 4E at a dilution of 3/8 pt/100 gal and applied as described for the other treatments. Pre-treatment (Mar) infestation of CRS on each tree was measured by in situ examination of 75 twigs (ca 1-2 yr old, and ca 9 inch long) and recording the presence or absence of live CRS. In 2 post-treatment evaluations (Dec and Mar ‘88), the infestation on 75 twigs/tree was determined in a similar manner, except that only adult females were included in the post-treatment evaluations. Additionally, in the post-treatment evaluations, up to 100 fruit/tree (100 were not always available, averages were 86 and 68 fruit/tree in the first and second post-treatment evaluations, respectively), were scored in situ as being infested with 0, 1-10, or >10 live or dead CRS. Infested fruit were categorized into those with more or less than 10 CRS/fruit because fruit are generally 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, CRS phenology was monitored weekly with pheromone traps and crawler traps.