DORMANT SEASON APPLICATIONS OF INSECTICIDES FOR THE MEALYBUG, FERRISIA GILLI, IN ALMOND, 2004-05

Ferrisia gilli is a newly described species of mealybug that has become established in pistachio and almond groves in California. During late 2004 observations were made that feeding from severe infestations of the mealybug in almond could be sufficient to cause complete defoliation of the tree. As a result, this trial was conducted during the winter of 2004-2005 to determine the effects of dormant insecticide treatments on mealybug density the following year. A total of 63 of the most heavily infested almond trees were chosen from an area of approximately 2.5 acre in size. Trees were organized into a CRD with nine replicates of five treatments and an untreated check. Treatments were applied on 17 Dec 2004 using a John Bean sprayer equipped with a hand gun applied at 150 psi. Applications were made at 200 gpa with the hand gun. The effects of insecticide treatments on mealybug populations were measured using bark samples from Dec 2004 through Mar 2005 and then spur samples in Apr and May. Bark samples were taken 1 week after treatment (WAT) (23 Dec), 4 WAT (12 Jan), 7 WAT (3 Feb), and 12 WAT (8 Mar) by excising a 3-inch diameter core sample of bark in an area of each tree trunk where aggregations of mealybugs were present. Cores were brought back to a laboratory and the number of live mealybugs was recorded. Spur samples were taken by evaluating 30 randomly collected spurs per tree and analyzed for the number of live mealybugs present. These samples were collected on 7 and 12 Apr, and on 15 May and are reported as mealybugs per 30 spurs as well as percentage spurs infested. Data from were analyzed by ANOVA using transformed data (squareroot (x+0.5)) with means separated by Fisher’s Protected LSD at P ≤ 0.05.