Efficacy of Soil-Applied Insecticides Against Carrot Weevil in Fresh Parsley, 2017

The carrot weevil (CW) is a serious pest of fresh parsley grown in muck soil regions of Ohio. The larval stage of this insect feeds internally within the crown and taproot of plants, leading to significant damage and the death of young plants. The efficacy of one foliar and three soil-applied insecticides were evaluated against CW in fresh parsley grown in muck soil during the summer of 2017 at The Ohio State University Muck Crops Research Station in Willard, Ohio. Parsley ‘Dark Green Italian’ was direct seeded on 26 Apr 2017 into eight triple-row beds, each 128 ft long × 5 ft wide and spaced 6 ft apart. Experimental units were 20 ft long × 5 ft wide plots containing three rows of parsley, each 18 inches apart. Three replications of each treatment were arranged in an RCB design. Insecticide compounds, formulations, and application rates are shown below in Table 1.

The foliar insecticide was applied using a conventional low-pressure boom sprayer equipped with AITTJ60-11004VP nozzles at 30 psi, 36.4 gpa, and 20-inch nozzle spacing on 16 Jun 2017 and 19 Jul 2017. Soil insecticides were applied using a modified pull-type liquid nitrogen applicator equipped with three soil shanks, TJ 8002VS nozzles at 22 psi, 48.13 gpa, and 18-inch shank spacing on 12 Jun 2017 and 19 Jul 2017. Soil insecticides were applied either once at the maximum rate, when plants were at the three-leaf stage, or twice with half the maximum rate applied each time. Soil applicator shanks were set to incorporate products 1 inch into the soil and within 2 inches of each row base, following the recommendations of product labels. One inch of follow-up irrigation was applied within 24 h of soil insecticide application, following label recommendations.

Root damage was assessed at harvest (29 Aug 2017) on 10 plants per plot in each replicate. Root damage was assessed on a scale of 1 to 7, with ‘1’ representing tunneling damage 1 cm below the crown (least damage) and ‘7’ representing tunneling damage 7 cm below the crown (most severe damage). The fresh weight of aboveground biomass harvested from three, 1 m sections of parsley was also assessed at harvest. Data were analyzed using ANOVA. Differences among means were determined using Fisher’s Least Significant Difference test (P ≤ 0.05).

CW pressure was moderately high in parsley plots during the experiment. There were no differences in fresh weights of parsley foliage among treatments at harvest on 29 Aug 2017. Single versus two applications of soil insecticides had no effect on the severity of parsley root damage. Contrasting foliar and soil insecticide treatments indicated that parsley plots receiving foliar applications of Baythroid XL had significantly less root damage on average (t = −2.21, P = 0.04), as well as significantly lower proportions of roots with severe damage (tunneling more than 5 cm below root crown) (t = −3.03, P < 0.01).

No phytotoxicity was observed.¹

Footnotes