Production Guide

Revised 01/19/2005

From Commercial Vegetable Production Recommendations, LCES Pub. 2433

Seed Potatoes

• Depending on variety, 25-30 bushels required to transplant an acre.

Bedding Mother Roots

• Soil temperature should be about 60 F for several days before bedding.
• Greater and early plant production if seed roots pre-sprouted by holding at 70-80 F and 85 percen to 90 percent relative humidity for 2-3 weeks.
• Cover seed potatoes with about 2 inches of soil. Beds are generally covered with clear or black plastic mulch after bedding, to warm soil.
• Punch small holes in plastic on side of the bed 2 weeks after covering. Helps provide better aeration and less rotting caused by carbon dioxide buildup.
• Six to eight weeks required to produce transplants

Transplanting Time

• South Louisiana - Late April through June
• North Louisiana - Early May through June

Depth to set Transplants

• 3-4 inches (several nodes below the ground)

Days from Transplanting to Harvest

• Beauregard - 90 to 110 days
• Hernandez - 120 days

Recommended Varieties

Beauregard - early maturing, light rose skin, orange flesh, resistance to soil rot disease; good sprout production; high yield potential; good shape; may tend to grow long in sandy soils; susceptible to root knot nematode and bacterial stem rot; good storage ability and excellent quality.

Hernandez - recommended for sandy soils. Good sprout producer; deep copper skin color, deep orange flesh, sets large numbers of roots, space 12-15 inches; susceptible to banded cucumber beetle; soil rot resistant.

Recommended Soil pH and Fertilizers

• pH 5.5-6.0. Apply 90-120 lbs/acre of phosphorus and potassium preplant and 30-45 lbs/acre of nitrogen preplant or as sidedress after 25-30 days.
• Soil pH below 4.8 should be limed up to 5.0-5.5. If below 5.0, soil should be limed to about 5.5-6.0.
• Upland soils may respond to a sidedressing of 20-30 lbs nitrogen and 50-75 lbs potassium per acre.
• Calcium 300-600 ppm; Magnesium 80-150 ppm.

Common Problems

• Soil insects including sweetpotato weevil, banded cucumber beetle, white grub, white-fringed beetle, wireworms, flea beetles.
• Diseases including soil rot, scurf, bacterial stem rot, storage rots.
• Cultural including nitrogen overfertilization, souring caused by excessive soil moisture, drought, skinning at harvest, poor shape, poor set, low yields, plant survival.
• Weeds including purple nutsedge, rice flat sedge, yellow sedge.

Recommended Herbicides

• Pre-emergence - Command 3ME
• Post-emergence (grass control) - Fusilade DX, Poast

Weed control is critical. For maximum yield, rows should be relatively free of weeds and grasses until full vine cover. Yellow nutsedge, rice flat sedge, carpet weed and pigweed are not controlled by Command herbicide. These may have to be controlled with rotation crops.

Harvest Information

• Harvested beginning in August and extending through November and into December if necessary.
• A bushel weighs 50 lbs.; however, the trade has adopted the 40-lb. box as its standard containter. Sweet potatoes sold right after harvest are sold as "green" potatoes and are not usually sweet when baked. Those held in storage for 7-8 weeks are sold as "cured" or "kiln dried." Kiln-dried indicates the potatoes are usually available around Thanksgiving. Sweet potatoes are field-graded at harvest into No. 1's and canners. Field-graded potatoes are either washed, graded and shipped; cured and placed in storage; or cured and then shipped.

Postharvest Handling

• Place harvested sweet potatoes in the curing room as soon as possible, preferably within 2 hours.
• Harvested sweet potatoes should be moved out of the field as soon as possible to prevent sunscald. Sweet potatoes to be sold green will have a better appearance and shelf life if they are cured.

Curing

• Accomplished by subjecting newly harvested roots to 85-90 F and 85 percent to 95 percent relative humidity for 4-7 days
• Helps heal cuts and bruises on the roots, making them less susceptible to disease infection during storage
• Improves root appearance and storage life

Storage

• Roots can be stored for several months if properly cured
• Ideal storage conditions after curing: 55-60 F and 85 percent to 95 percent relative humidity. After having been stored under high humidity, the roots should be held at a lower relative humidity for 2-3 days to reduce skinning during packing operations. This can be accomplished by moving potatoes out of high humidity storage into the packing area 2-3 days before packing.

Special Cultural Information

• Virus-tested Foundation or certified seed should be part of a sweet potato program to maintain the highest quality roots.
• Plants should be cut 1 inch above the soil line rather than pulled. This reduces transmission of several diseases including scurf, soil rot, circular rot, etc. from plant beds to the field. Cut plants are almost 100 percent weevil free going to the field. Holding cut plants 3-4 days before transplanting encourages fibrous root development and increases plant survivability.
• Soil insecticides Mocap or Lorsban should be used ahead of planting to reduce white grub, cucumber beetle and wireworm damage.
• Weekly application of recommended pesticides (PenncapM, Imidan, Thiodan, Sevin) beginning 2-3 weeks after transplanting will help reduce soil insects.
• 2-4 ounces of Imidan dust/bushel should be applied at harvest for weevil control in storage. Good sanitation practices are essential for maximum weevil control (destroying plant beds, chopping and exposing sweet potatoes left in the field after harvst, cleaning storage facilities).
• Harvest seed potatoes early and treat with Imidan for maximum weevil control. Early harvest while temperatures are high will encourage weevils to pupate and emerge, bringing them in contact with the Imidan.

Contact Information:
Telephone: 318-435-2155 Fax: 318-435-2110
P.O. Box 120
Chase, Louisiana 71324
email: lbuckley@agcenter.lsu.edu