Different application frequencies of tubli root extracts, Derris elliptica, against the diamondback moth (DBM) were assessed to determine the impact on the growth and yield of pechay, Brassica rapa crop. The experiment was arranged in a randomized complete block design, with four treatments replicated three times. The application started a day after transplanting. The treatment of the extract given seven times at 3-day intervals after transplanting (T1 ) significantly resulted in lower mean DBM populations of 1.90, 0.70, and 0.30 at 7, 21, and 28 days after transplanting, respectively. Relative to plants applied with tubli root extracts four times at 6-day intervals after transplanting (T2 ), the mean reductions of the moth were 2.50, 0.96, and 0.83, respectively. It was evident that plants treated with tubli root extracts seven times at 3-day intervals (T1 ) were significant in incurring the minor damage of only 16% at harvest. The treatments helped obtain good crops (98.36 g/hill), a high yield (7.17 kg/plot), and a higher percentage of marketable plants (91.77%/plot) compared to other treatments of the extract with lesser frequencies, like four times at 6-day intervals after transplanting (T2 ), three times at 9-day intervals after transplanting (T3 ), and plants without treatment (T0 ). Overall, the growth of pechay was not affected by the different application frequencies of tubli root extract.