**Background:** Pesticide residues in food are a major concern for human health, with dietary intake being the primary exposure route. Squash (Cucurbita pepo) is a minor crop in the Republic of Korea (ROK), consumed as fruit, leaf, and seed. While MRLs exist for some pesticides in squash fruit, data for squash leaf are limited. This study aimed to develop and validate a UHPLC-MS/MS method to quantify residues of four carboxylic acid amide and triazole fungicides—dimethomorph, mandipropamid, myclobutanil, and metalaxyl—in squash fruit and leaf, determine their dissipation half-lives, and estimate dietary health risk.
**Methods:** Squash plants were grown in a greenhouse in Cheongju-si, ROK (temperature 13.7–20.9 °C, humidity 63.0–90.9%). Each pesticide was applied three times at 7-day intervals at recommended dosages (dimethomorph 45 g a.i./10a, mandipropamid 20.331 g a.i./10a, myclobutanil 7.2 g a.i./10a, metalaxyl 45 g a.i./10a). Samples were collected 0, 3, 5, 7, and 14 days after the last application. Pesticides were extracted using an EN-QuEChERS kit and analyzed via Shimadzu LCMS-8045 with UHPLC Nexera X2 and Kinetex C18 column. Method validation assessed linearity (0.005–0.1 mg/L), recovery (76.4–101.9%), and precision (RSD <4% for all). Dissipation kinetics were modeled using first-order equations. Dietary risk was calculated using the hazard quotient (HQ = EDI/ADI), with intake data from 43,602 individuals (National Institute of Food and Drug Safety Evaluation, 2019).
**Key Results:** Initial residue levels in squash fruit were 0.36 mg/kg (dimethomorph), 0.29 mg/kg (mandipropamid), 0.06 mg/kg (myclobutanil), and 0.33 mg/kg (metalaxyl). In squash leaf, initial residues were 69.88, 39.41, 11.65, and 31.71 mg/kg, respectively—95 to 193 times higher than in fruit. Half-lives in fruit were 2.1 days (dimethomorph), 4.6 days (mandipropamid), 4.7 days (myclobutanil), and 2.7 days (metalaxyl). In leaf, half-lives were 4.9, 8.1, 8.2, and 5.0 days, respectively. Correlation coefficients for dissipation kinetics ranged from 0.94 to 0.98. On day 0, metalaxyl residue in squash fruit (0.33 mg/kg) exceeded the ROK MRL (0.2 mg/kg) at 165% and the EU MRL (0.01 mg/kg) at 3300%. In squash leaf, metalaxyl initial residue (31.71 mg/kg) was 106% of the ROK MRL (30 mg/kg). For all other pesticides, residues at harvest were below respective MRLs. HQ values for total surveyors ranged from 1.75 × 10⁻⁵ to 2.39 × 10⁻³ across all pesticides and time points. For true consumers, HQ values ranged from 5.36 × 10⁻⁵ to 3.91 × 10⁻¹. All HQ values were <1, indicating no significant health risk.
**Clinical Implications:** This study provides the first comprehensive data on dissipation patterns and dietary exposure risk for these four fungicides in squash leaf. The findings support the establishment of MRLs for mandipropamid in squash fruit and for dimethomorph and mandipropamid in squash leaf in the ROK, where such limits are currently absent. The HQ values confirm that dietary intake of these pesticides from squash fruit and leaf poses no appreciable health risk to either the general population or true consumers, even at initial residue levels. The data also support the current pre-harvest intervals of 3 days for dimethomorph and 7 days for myclobutanil and metalaxyl in squash fruit.