The white grub, Diaprepes abbreviates L. (Coleoptera: Curculionidae), is a significant pest of yam tubers and the second cause of tuber rot in Haiti. Larval feeding inflicts severe damage to tubers, leading to notable losses due to decreased tuber quality, reduced marketability, and increased susceptibility to secondary parasites and pathogens. This study examined the influence of planting and harvesting dates on the vulnerability of yam tubers to white grub infestation and the resulting tuber quality across 24 farmers’ fields. At harvest, we assessed the level of tuber infestation, white grub density, and the tuber quality index. The results indicated that 85% of grub populations were found in fields planted on the traditional date. In addition, 69.5% of tuber damage occurred in early-planted fields with fewer tubers damaged (30%) when harvested early. In contrast, in fields planted 30 days after the traditional date, the harvest date did not affect tuber infestation and damage by the pest. Overall, both planting and harvest dates impacted the quality grade of yam tubers. Delayed planting by 30 days and early harvesting (34^th -38^th week after planting) improved the marketability of yams. These findings highlight the importance of optimizing planting and harvest schedules to better manage white grub infestation and enhance the marketability of yam tubers.

We studied 24 neighboring farmers' fields, split into two main fields with planting date as the main field factor and harvest date as the subfield factor. The main factor had two levels: planting on traditional date (DAP 0), and planting 30 days after the traditional date (DAP 30), with 12 fields at each level. The traditional date for planting yams corresponds to the yam planting peak which occurs in April, when most farmers set up their plots. The second planting date (DAP 30) was chosen based on information provided by farmers reporting that plots not planted in April are planted in late May or early June during a second planting period. The second factor, harvest date, consisted of three levels: harvesting at the 34^th, 38^th, and 42^nd week after planting, with four replications of each level. 

Data were recorded at harvest time by randomly selecting five planting mounds per treatment field, i.e., five planting moundings per harvest date. Grub density and hole density per tuber were assessed by counting the number of grubs in each planting hole and the number of holes in each tuber. Hole size in yam tubers, including diameter and depth, was measured using a palmer and a ruler, respectively. Yam harvest density was determined by counting the number of tubers harvested in each planting hole. Tuber weight was measured with a scale, BAICO (PRI PA’W, Jérémie, Haiti), and the tuber quality index was calculated by dividing the number of undamaged tubers by the total number of tubers harvested per planting hole.