If I amend my soil with your recommendations, will a pesticide mess it up again?

Answered by Hunter McBrayer

Generally speaking, most of insecticides that will be applied to vegetable plants will be a foliar application. This certainly will not impact percentages of organic material in soil or the soil chemistry (pH and nutrients). Some pesticides are active in the soil and could impact biota (microorganisms) in the soil, but foliar applications will reduce or prevent this. Take a look at the Extension publication below. You will see some insecticides that are minimally harmful and have short efficacy times. The key to this and any other application is timing. 

Cucumber, Squash, Melon & Other Cucurbit Insect Pests | Home & Garden Information Center (clemson.edu)