Try diatomacious earth. Basically it is a fossil that has a high liquid absorbtion capability and when the insect walks on it, it absorbs the water from their exoskeleton and causes them to die. Chemical composition is silica sodium magnesium and iron so likely will not overfert by adding it to the soil surface. Just be careful applying it maybe wear something over ur mouth (bandana, painter's mask) because it can be harmful to inhale or ingest certain types.

Edit: Hmm I guess they lay their eggs in the webbing so I don't know how well this would work but very good preventative method. However if they walk on soil sometimes this would be good.