Influence of Planting Date, Harvest Date, Soil Type, Irrigation and Nematicides on Pest Numbers, Yield and Quality of Sweetpotatoes in the Mississippi Delta Larry Adams and Dick Hardee, USDA-ARS, Stoneville, MS Results of harvesting heavy clay plots. Soil Comparison: Top – Sandy Loam Bottom – Heavy Clay 2003 Sweetpotato Damage Scoring Scale 50’ of Row Harvested Rating Scale is 0-3; 0 – No Damage seen in the sample 1 – 5-10% of the potatoes in the sample are damaged 2 – 10-25% of the potatoes in the sample are damaged 3 - > 25% of the potatoes in the sample are damaged Note: Wireworm and Grub feeding damage. Introduction In 2002 sweetpotato producers in Mississippi suffered great losses due to the weather. Precipitation at harvest resulted in much interest for research in the area of planting date and harvest date relative to insect damage, yield and quality of sweetpotatoes. USDA, ARS, SIMRU at Stoneville, Mississippi, in cooperation with Alcorn State University and Mississippi State University, conducted studies at three locations during the 2003 growing season to address concerns of optimal planting and harvest dates and their affects on insect damage, yield and quality of sweetpotatoes. Materials and Methods The Beauregard variety was planted at all locations. Two soil types at the Stoneville, MS location, sandy loam and heavy clay, and one soil type at the Mound Bayou, MS and Holly Buff, MS locations, sandy loam, were evaluated. Fertilization, insecticide and herbicide applications were made as needed. Two transplanting dates per location, mid May and mid June, and four harvest dates per location, 90, 97, 104 and 111 days after transplanting were evaluated. The Stoneville, MS location plots were irrigated and non-irrigated while all other locations were non-irrigated. Fifty foot of row was harvested from irrigated/non-irrigated for each planting date, each harvest date and each soil type. Yield comparison and damage levels were rated from each sample. Insect populations were monitored throughout the growing season with the “Bug Vac” and 15 inch sweep net to compare sampling techniques. Summary Results of USDA, ARS, SIMRU 2003 studies indicate a slight increase in yield and a significant increase in US#1 potatoes as planting date and harvest date increased at all locations with the exception of planting date two at the Holly Buff, MS location. These test also illustrated a progressive increase in insect damage, particularly wireworm and white grub, as planting date and harvest date were prolonged. Total marketable yield was higher in the heavy clay plots at the Stoneville, MS location but a decrease in the percent US#1’s and uniform shape was observed. Harvesting the heavy clay plots at the Stoneville, MS location was a challenge due to large clods of soil coming across the conveyer belt slowing the harvest progress considerably and leaving the field in very poor condition needing several trips across it to prepare for the next year. Economically, heavy clay soil is unacceptable in the production of sweetpotatoes in the Mississippi delta. Significant differences were not seen comparing the irrigated and non-irrigated plots at the Stoneville, MS location due to timely rains received throughout the 2003 growing season. The 2003 comparison of the sweetpotato Bug Vac and the conventional sweep net showed the Bug Vac to be much more efficient when sampling sweetpotato fields for insect populations. Although no nematode damage was evident in the test samples, Telone II treated plots showed a significant yield response over the non-treated plots. Sweetpotatoes in the non-treated plots were stunted while vegetative growth did not appear to be affected. Acknowledgements The authors would like to thank Chris Johnson, Owen Houston, Debbie Boykin and Alcorn State University’s research farm at Mound Bayou, MS for their assistance with these projects.