Comparison of drip and foliar-applied insecticides for mealybug management in grapes, 2024

Foliar and drip applications of flonicamid (Beleaf 50SC) and flupyradifurone (Sivanto Prime) were compared to determine which application on grape vines would more effectively manage mealybug, Planococcus ficus. This trial was conducted in a 30-year-old “Thompson Seedless cv.” of raisin grapes in Selma CA. The experiment layout was a randomized complete block design with 4 replicates. Within each block, each treatment was applied to the trunk and canopy of 5 vines, with a 2 vine buffer between each treatment. Sivanto Prime with Dyne-Amic at 14 oz/acre (non-ionic adjuvant at a rate of 0.5% v/v) applied to the trunk and canopy, Beleaf 50SG with Dyne-Amic 5.6 at oz/acre applied to the trunk and canopy, Beleaf with Pentra Bark (a non-ionic wetting agent at a rate of 0.5% v/v) 5.6 at oz/acre applied to the trunk and canopy, and Beleaf 50SG 5.6 at oz/acre applied to the soil via chemigation, were compared to an untreated control plot. Each treatment was applied once on 2 Jul 2024, using R. L. Flomaster Standard 2-Gallon Sprayers (Root-Lowell Manufacturing Co.) at a rate of 100 gallons per acre. Before treatments were applied, mealybug infestation was estimated using trunk ratings conducted 1 day prior. The rating scale was from 0 to 3 where 0 = no mealybug damage, 1 = honeydew (indicating the presence of mealybugs), 2 = mealybugs and/or damage on trunk and/or leaves, and 3 = severe mealybug damage to trunk and leaves. These ratings were analyzed using Pearson’s chi-square test. Before treatment, ratings showed a significant difference between treatment plots (χ² = 25.89, df = 12, P = 0.011). Before treatment, trunk ratings between Beleaf 50SG with Dyne-Amic and soil-applied Beleaf were similar (t-ratio = 0.667, P-value = 0.963) and generally higher trunks in the other treatment areas. Pre-treatment trunk ratings showed no significant differences between blocks (χ² = 6.01, df = 9, P = 0.739).

On 30 Jul, trunk and harvest counts were evaluated on each treated vine in each block to measure mealybug presence post-treatment. Trunk counts involve stripping bark from the vine trunk for 3 min, after 3 min of bark stripping, the timer is stopped, and mealybugs are counted (adults and nymphs). For harvest counts, 3 grape clusters from each vine in each treatment were inspected for mealybug presence, and clusters were rated as 0 = no mealybug detected, 1 = mealybug present, 2 = 2 or more mealybugs and/or honeydew, or 3 = multiple mealybugs and/or honeydew present on the cluster. Data were compared using a generalized linear model with treatment (5 levels) assigned as a fixed effect. Finally, we compared the influence of each treatment by ANOVA, and the means were separated using Tukey’s HSD test. We found no differences between the untreated vines, compared to Sivanto with Dyne-Amic (z-ratio = −4.15, P-value = 0.6242), Beleaf with Dyne-Amic (z-ratio = 2.20, P-value = 0.945), and Beleaf with Pentra Bark (z-ratio = 2.00, P-value = 0.961), or Beleaf 50SG (z-ratio = −2.10, P-value = 0.953) (Table 1).¹

Footnotes