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Sweet Potato – Diseases 284 Midwest Veg Guide 2022 Fertilizing pH: Maintain the soil pH above 5.0. Before planting, apply 30 pounds N per acre, 0 to 75 pounds P 2 O 5 per acre, and 0 to 250 pounds K 2 O per acre based on soil test results and recommendations from your state. Set the slips with a starter solution at the rate of 1 cup (8 fl. oz.) per plant. Sidedress with 30 to 50 pounds N per acre three to four weeks after transplanting on irrigated sands. Finer textured soils usually do not need sidedressing. Reduce the amount of fertilizer N applied by the value of N credits from green manures, legume crops grown in the previous year, compost and animal manures, and soils with more than 3 percent organic matter. The total amount of N from fertilizer (including starter) and other credits should be 80 pounds per acre or less. Harvesting The last month or so of production is when sweet potato roots put on all their size. Thin, long roots indicate that they are still bulking up. Harvests can begin when roots reach a desired size but should be finished before regular freezing temperatures begin. Tops can freeze off without damaging roots right away, but the decomposing tops can eventually lead to rots in the roots. As soil temperatures go below 65° F tuber growth stops. Remove vines by cutting with a rotary mower 5 to 7 days before harvest to toughen the skin. Plowing out and hand- collecting sweet potatoes is a common harvest method because their thin skins are easily damaged from chain- diggers. Dig only those potatoes that can be picked up immediately. Potatoes will sunburn if left in direct sunlight for more than an hour. To prevent skinning and bruising use cotton gloves when placing potatoes in crates. Field grading is important. Overnight temperatures below 55° F can chill any dug sweet potatoes that were not collected and cause internal breakdown in storage. Flavor improves and sweetens a few weeks after digging. Uncured sweet potatoes will last 3 to 6 months in storage. To cure them for 6- to 12-month storage, immediately place them at 80° to 85° F and 85% to 95% humidity for 4 to 7 days. After curing, the temperature may be gradually dropped to 58° F. Hold this temperature until potatoes are marketed or used for producing slips. Sweet Potato – Diseases Reviewed by Dan Egel – Sept 2021 Recommended Controls Black Rot of Sweet Potatoes - Ceratocystis Fungus Non-Pesticide Plant disease-free seed and/or resistant varieties. Follow 3-4 year crop rotations. Prevent bruising. Cure and store only healthy, blemish-free tubers, and maintain proper storage temperatures. Pesticide Mertect 340-F (SC) (thiabendazole) | 8 fl. oz. per 7.5 gal. of water. One application only. REI: 12-hour. PHI: 0-day. FRAC 01. Foot Rot of Sweet Potatoes - Plenodomus Fungus Non-Pesticide Plant disease-free seed and/or resistant varieties. Follow 3-4 year crop rotations. Prevent bruising. Cure and store only healthy, blemish-free tubers, and maintain proper storage temperatures. Pesticide Mertect 340-F (SC) (thiabendazole) | 8 fl. oz. per 7.5 gal. of water. One application only. REI: 12-hour. PHI: 0-day. FRAC 01. Scurf of Sweet Potatoes - Monilochaetes Fungus Non-Pesticide Plant disease-free seed and/or resistant varieties. Follow 3-4 year crop rotations. Prevent bruising. Cure and store only healthy, blemish-free tubers, and maintain proper storage temperatures. Pesticide Botran 75W (dichloro-nitroaniline) | Use as seed potato dip or plant bed spray. REI: 12-hour. PHI: 0-day. FRAC 14.