Tropical small-holder farmers rely on sustainable food production. Crop seed predation by ants can cause substantial yield loss and result in high pesticide use. We conducted field experiments and questionnaire-based surveys aiming to assess the effect of sown-seed predation on four crop species (Cucumis sativus, Daucus carota, Capsicum frutescens and Solanum melongena) in 15 vegetable gardens and the resulting impact on the net income of Indonesian farmers. Furthermore, we tested a commonly applied insecticide and herbicide for seed, seedling and plant protection aiming to understand their effect on ant seed predation. We found that the mean percentage of seeds removed per garden was 42.0%, 49.4%, 48.0% and 50.6% for C. sativus, D. carota, C. frutescens and S. melongena, respectively, halving the farmers' income after considering initial and operational costs. Insecticide and herbicide treatments did not affect seed predation success or overall ant abundance, although they had positive and negative effects on ant species-specific abundance. High overall ant abundance caused high seed predation rate in all gardens as a result of a functional redundancy of ant species, which compensated for pesticide-related species loss. Environmentally-friendly and more sustainable practices such as overseeding or seedling production in nurseries could substitute for these inefficient approaches of chemical pest control, although this requires further research.