I’m not sure if a study has been done as to the minimum ratio of alcohol/water plus soap for effectiveness. However, you are right to be concerned about burning plants. With alcohol sprays, always test a solution on a small area before spraying an entire plant or crop; some plants may be more sensitive than others. You might try a solution with a small percentage of alcohol to water and work up to determine the minimum you can use and still have it be effective. As to vinegar, same precautions. One must be very careful about proportions, or as you have read, the vinegar’s acetic acid can kill plants (at higher concentrations, vinegar is used as an herbicide). Some sources suggest avoiding using it at all, especially on vegetables or flowers. Others suggest 3 parts water to 1 part vinegar, and only spraying leaves. If you try this route, you might try diluting the solution even further, then testing on a small area first. Hope this helps!
I’m not sure if a study has been done as to the minimum ratio of alcohol/water plus soap for effectiveness. However, you are right to be concerned about burning plants. With alcohol sprays, always test a solution on a small area before spraying an entire plant or crop; some plants may be more sensitive than others. You might try a solution with a small percentage of alcohol to water and work up to determine the minimum you can use and still have it be effective. As to vinegar, same precautions. One must be very careful about proportions, or as you have read, the vinegar’s acetic acid can kill plants (at higher concentrations, vinegar is used as an herbicide). Some sources suggest avoiding using it at all, especially on vegetables or flowers. Others suggest 3 parts water to 1 part vinegar, and only spraying leaves. If you try this route, you might try diluting the solution even further, then testing on a small area first. Hope this helps!