Laboratory and greenhouse experiments were carried out to study the effect of calcium and potassium carbonate in increasing the potency of some biopesticides. The results of laboratory study indicated that xentari gave the highest RL_so value of 77.91 days indicating long persistence and high toxicity against PTM followed by Verotecto and Agerin, while Dipel 2x, Ecotech and MVPII caused the lowest effects. Also xentari gave the highest RL_so value of 36.99 days in greenhouse while Verotecto gave the lowest result where its RL_so was 9.95 days The results provided evidence that the initial and residual effect of the tested biopesticides can be markedly increased by using calcium or potassium carbonate at 0.1% in combination with each of the candidate biopesticides. The RL_so values indicated that all tested biopesticides when combined with potassium carbonate at 0.1% were more effective than calcium carbonate in protecting potato plants against PTM in laboratory and greenhouse. This may be attributed to the fact that the addition of such salts change pH of the gut, being more alkaline and thus enhancing the endotoxin breakdown and release of toxic fragments.