Midwest Vegetable Guide - 2022 - 284

Sweet Potato - Diseases
Fertilizing
pH: Maintain the soil pH above 5.0.
Before planting, apply 30 pounds N per acre, 0 to 75 pounds
P2O5 per acre, and 0 to 250 pounds K2O 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 handcollecting
sweet potatoes is a common harvest method
because their thin skins are easily damaged from chaindiggers.
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.
284
Midwest Veg Guide 2022
Midwest Vegetable Guide - 2022

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