Evaluating the application interval of in-season drip and foliar insecticides for vine mealybug management in grapes, 2024

The efficacy of in-season drip applications of spidoxamat (Pridixor 75SG) and foliar applications of spirotetramat (Movento 240 SC) with Dyne-Amic (nonionic adjuvant at a rate of 0.5% V/V), and spidoxamat + flupyradifurone (Plenexos Smart) with Dyne-Amic were compared to determine if treatment interval impacted density of a mealybug, Planococcus ficus compared to an untreated control. Research was conducted in a 17-year-old ‘Pinot Gris’ vineyard at John Kautz Farms in Lodi, California. The experimental layout was a randomized complete block design with 5 replicate blocks (rows). Each of the 4 treatments was applied randomly to 10 consecutive vines in each row and treatments were separated by a 2-vine buffer. The Movento–Movento treatment included 2 foliar applications of Movento 240 SC with Dyne-Amic, applied at 6.3 oz/acre once in May and once in June. The Plenexos Smart–Pridixor treatment included 1 soil application of Pridixor at 3.8 oz/acre in May and 1 foliar application of Plenexos Smart with Dyne-Amic at 19.0 oz/acre in June. The Pridixor–Movento–Plenexos Smart treatment included 1 soil application of Pridixor at 3.8 oz/acre in May, 1 foliar application of Movento 240 SC with Dyne-Amic applied at 6.3 oz/acre in June, and 1 foliar application of Plenexos Smart with Dyne-Amic at 19.0 oz/acre in July.

On 11 April and 15 May before treatment applications, the level of mealybug infestation on the trunk was estimated based on a 0–3 trunk rating scale. When no mealybug was detected, trunks were rated 0 = no mealybug damage, rating 1 = honeydew present (indicating the presence of mealybugs), rating 2 = mealybugs and/or trunk damage, and rating 3 = severe mealybug damage to the trunk. Ratings were compared in a 2 × 2 contingency table with treatments separated using Pearson’s chi-square. Pretreatment ratings showed significant differences among rows (X² = 48.13, df = 12, P-value < 0.001) and no differences among the treatments within each row (X² = 7.76, df = 9, P-value = 0.559).

We recorded the number of mealybugs found on 1 leaf per vine (50 leaves per treatment) every 2–4 weeks between 23 May and 8 August. At the end of the season on 29 August and 5 September, we conducted cluster harvest ratings and trunk counts on each treated vine in each row, respectively. 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. 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). Data collected were modeled using a generalized linear model with a Poisson or zero-inflated Poisson distribution as needed. Treatment (4 levels) was assigned as a fixed effect and vine (10 levels) and rows (5 levels) as random effects. Finally, we compared the influence of each treatment by ANOVA and means were separated using Tukey’s HSD test.

Vines treated with the Movento–Movento on 5 September 2024 had significantly fewer nymphs and adult mealybugs on the trunks compared with the untreated control (z-ratio = 3.01, P-value = 0.014) and—Pridixor–Plenexos Smart-treated vines (z-ratio = 3.56, P-value = 0.002). Fewer mealybugs were recorded on Pridixor–Movento–Plenexos Smart-treated vines compared with Pridixor–Plenexos Smart (z-ratio = −2.87, P-value = 0.021) (Table 1). Cluster ratings were compared in a 2 × 2 contingency table with treatments separated using Pearson’s chi-square. Cluster ratings on 29 August 2024 showed no significant differences among treatment cluster ratings: (X² = 11.71, df = 6, P-value = 0.069). Leaf count data were at 6 time points during the growing season, and the average for each treatment is reported below. Compared with the untreated control, significantly fewer mealybugs were found in the leaf canopy of vines treated with Movento–Movento (z-ratio = 3.69, P-value = 0.001), Pridixor–Plenexos Smart (z-ratio = −3.24, P-value = 0.007), and Pridixor–Movento–Plenexos Smart (z-ratio = −4.67, P-value ≤ 0.001) (Table 1).¹

Footnotes