Timing Lorsban Applications for CRS Control, 1986

Abstract

Abstract A randomized complete block experiment with 9 single-tree replicates/treatment and 5 treatments was conducted in a field of mature navel orange trees at the University of California Lindcove Field Station, Exeter, Calif. Four blocks were in ‘Fisher’ variety navel oranges and 5 blocks were in ‘Old Line Washington’ navel oranges. Pretreatment densities of CRS were evaluated in late April 1986 by examining 75 9-inch twigs (1 yr old) from each tree. Each twig was scored in situ as being infested or not infested with live CRS. Trees were assigned to the 9 blocks on the basis of pretreatment CRS density so that within each block initial CRS density was similar among trees. Consequently, trees within a block were not necessarily adjacent. Treatments then were assigned randomly to trees within each block. The 5 treatments were 5 different times for application of an identical amount of Lorsban 4 E (3/8 pt/100 gal applied by handguns from both ground and tower positions at 500-550 psi, and 17 gal/tree). Maximum and minimum temperatures recorded at the Lindcove Field Station were used to calculate degree-days for CRS development (single sine wave method, lower threshold of 53°F; no upper threshold), and pheromone traps were used to monitor male flight. Cumulative degree-days were calculated from 25 May, which was the beginning of the second-generation male flight. Posttreatment samples were taken in mid-October 1986 (fruit and twig evaluation) and again in mid March 1986 (fruit evaluation) and early April 1987 (twig evaluation) by in situ examination of 75 9-inch twigs and 100 fruit from each tree. The twigs were scored as infested or not infested with live CRS. Fruit were scored as having 0, 1-10, or >10 live or dead CRS, because fruit are downgraded in the packinghouse when infested with approximately 10 or more live or dead CRS. Therefore, counts of live and dead scale on fruit were used to assess how well a treatment protected the fruit from becoming infested and being downgraded; counts of live scale on twigs were used to assess how well a treatment suppressed population growth.