Mid-season management of Gill’s mealybug in Pistachios, 2023

Ferrisia gilli is a significant pest of pistachios that is commonly managed through an insecticide application in late May that targets the emergence of first-instar nymphs. Left unmanaged, these nymphs will become adults in July and initiate a second generation of mealybugs that can cause significant reductions in pistachio yield and quality. During 2023, we conducted a trial in a commercial pistachio orchard near Lost Hills, Kern Co. CA to evaluate the effectiveness of 12 insecticide treatments applied during peak crawler emergence. The trial was organized as an RCB design with 6 blocks of single-tree plots. Foliar treatments were applied on 30 May using a handgun at 150 PSI at a water volume of 200 gpa. One treatment (Sivanto) was also applied by mixing the pesticide into two 5-gallon buckets filled with water, after which a tiny hole was drilled near the bottom of the bucket to allow the solution to trickle out over a period of approximately 2 hours. Buckets were placed near drip emitters that were located approximately 4 feet on either side of the tree trunk during standard orchard irrigation. All foliar treatments were made with the addition of the surfactant Dyne-Amic at a rate of 16 fl oz per 100 gallons of spray solution (0.125%).

Mealybug density was determined on 22 May and every 2 to 4 weeks thereafter through harvest. This included 3 evaluations during the mealybug generation being targeted by the spray (28 June, 11 July, and 27 July) and 3 evaluations during the subsequent generation (22 August, 6 September, and 12 September) with the final evaluation taking place 1 week before harvest. On each evaluation date, the number of mealybugs was counted in each of 10 clusters per tree. Data of the average mealybugs per cluster were analyzed by ANOVA as a CRD due to insignificant block effects on all evaluation dates (> 0.48) using transformed data (sqrtx + 0.5) with treatment means separated by Fisher’s Protected LSD (P = 0.05).

Prior to treatment, there were no significant differences in pre-counts that averaged 0.13 mealybugs per cluster across treatments (Table 1). Following treatment, Assail, Centaur, and MBI-306 reduced mealybug populations on at least 5 evaluation dates, including a > 50% reduction on the final evaluation date 1 week before harvest. Sefina, Sequoia, Movento, and Beleaf each reduced mealybug densities on 1 evaluation date, but not to levels that were significantly lower than the untreated check on the final 2 evaluation dates. Mealybug densities were not significantly reduced compared to the untreated check on any evaluation date in plots treated with Aza-Direct, Venerate, Fujimite, or with a soil or foliar application of Sivanto.

Acknowledgments

This research was supported in part by the California Pistachio Research Board and industry gifts of pesticides and research funding.

Author contributions

David Haviland (Writing—original draft [lead], Writing—review & editing [equal]), and Stephanie Rill (Writing—original draft [supporting], Writing—review & editing [equal])