Louisiana sweet potatoes battle back

Sweet potatoes are roots, not tubers, so they require a lot of handling even after a mechanical harvest.

Hurricanes Gustav and Ike put a severe dent in the Louisiana sweet potato industry last year, but growers are fighting back. Acreage is down a bit, but growers and university researchers are focusing on ways to reverse a bad year.

The hurricanes, along with Tropical Storm Fay, dumped some 40 inches of rain on parts of northern Louisiana in late summer and fall of 2008. That moisture caused about 60 percent of the state’s sweet potato crop to break down, either in the ground or in storage, according to Tara Smith, Louisiana State University Agricultural Center extension specialist and research coordinator at the LSU AgCenter Sweet Potato Research Station in Chase.

"It’s always a potential risk, in the situation we’re in," Smith says of farming in a state known for hurricanes and late-season rains, though the 2008 convergence of disasters was a rare event. Timeliness leading to earliness may be of great benefit to producers.

Arthur Villordon, another staffer at the LSU AgCenter, has demonstrated that good soil moisture at planting is crucial for sound early establishment of sweet potato roots. Smith says that within 20 days after transplant of the slips, storage root initiation has begun. If the plant is stressed during this period, lignified roots will result and will not be able to develop into commercial sweet potatoes. Soil moisture deficiency has been documented as a contributor, but other factors may also stress the plants and reduce root set.

"If moisture is withheld at that critical period of time, it will negatively affect your planting situation," Smith says. She recommends that soil moisture be at 50 percent field capacity during and shortly after the planting period.

There are several factors that contribute to good early stands, she notes. One is to maintain good seed stock. The LSU AgCenter Sweet Potato Station produces virus-tested foundation seed stock every year, selling about 15,000 50-pound bushels of it, and the AgCenter recommendation is that growers supplement their on-farm seed programs with foundation seed each year. It is also recommended that seed be used no longer than three years or three generations removed from foundation stock to ensure that growers have the viable and productive seed program so necessary to this vegetatively propagated crop.

Center pivot irrigation and a well-timed harvest can help avert late- season weather disasters to the Louisiana sweet potato crop.

Early control of soil insects like cucumber beetles, white grubs and sugar cane beetles is also crucial. An IPM approach is recommended, and judicious use of insecticides is a major component of such programs. "We do rely on chemicals for sweet potato insects in the Southeast," Smith says, and timely preplant and lay-by applications to the soil can be a part of that. An early treatment with a preplant such as Lorsban or Brigade targets early larval stages present in the soil. After 30 days or so the vines have covered the rows and pesticides can’t be incorporated into the soil. Season-long scouting of adult stages is recommended because insect pressure is heavy throughout the growing season. Rotational crops can assist in long-term management of all pests, an example being the use of corn or grain sorghum as a sweet potato rotation to curb reniform nematode populations.

"We try to keep the crop weed-free for the first six weeks," Smith adds. In sweet potatoes, several weeds can be problematic, including alligator weed, purple and yellow nutsedge and several pigweed and morning glory species. In the short term, growers successfully use Valor as a preplant, Command as an over-the-top application just after transplant and Select, Fusilade or Poast to control troublesome grasses within the season. Mid and late-season weed escapes often necessitate hand-weeding. Smith says this is expensive and time-consuming, but it’s the only way to make sure weeds don’t affect yield or quality of the crop late in the season.

Grower Ken Thornhill is definitely on board with these early techniques, especially the advice on soil moisture. He is growing 750 acres of sweet potatoes in Franklin Parish, and he has converted some irrigation to center pivot sprinklers. He has three pivots, the rest of his ground being in furrow irrigation. The sprinklers are more water-efficient and allow him to have better control and timing on his irrigations.

On his farm, and as a member of the Louisiana Sweet Potato Commission, he gives his crop a healthy start with strong seedlings. He utilizes winter and spring moisture where possible for his earliest plantings and saves the pivot fields for last because he can sprinkle on the moisture they need if the fields are dry.

Another innovation Thornhill is taking advantage of is a new variety released by LSU’s breeding program, Evangeline, which was released in 2007. He has 150 acres; the rest of his fields are planted with the Beauregard variety.

Ken Thornhill and his son Shawn are sold on the Louisiana sweet potato business-even after last year’s hurricanes.

"It has a very high sucrose content. It is the sweetest potato you’ve ever eaten," he says of the Evangeline, but he also likes that it appears to have some extra resistance to rot at the end of the year. Last year he had few acres of the variety, but found that only about 10 percent of them rotted in the ground compared to over 60 percent of the Beauregards.

It does, however, have one drawback. "It’s more difficult to manage in the seed beds," Thornhill says. In addition, it is susceptible to sclerotial blight in the seed beds, and the seed potatoes do not produce as many slips that can be transplanted, compared to the Beauregard variety. Smith acknowledges this disadvantage, and says the university is doing tests to counteract the problem. One recommendation is to pre-sprout the seed potatoes before planting by increasing air temperature while they are still in storage. Evangeline seed that was pre-sprouted prior to bedding this year performed very well.

Smith verifies that the Evangeline did hold up "very well" during the wet harvest conditions last year. Although the variety appears to take a week or two longer than Beauregard to reach ideal harvest size (maximum number of U.S. #1 grade), its stability in flooded fields is a huge plus. She notes that Don LaBonte is the LSU plant breeder who developed the Evangeline variety.

Smith says that attention to details of seed bed preparation and timing can help a grower get a jump on a good season. She cautions against piling seed potatoes on top of each other in the bed, which tends to produce spindly slips and a slow-starting transplant. The use of fungicides labeled for sweet potatoes-Botran, Mertect and Quadris-will provide some insurance against disease, and she recommends plastic mulch to speed up seed sprouting, a practice common among sweet potato growers now.

Agreeing with Thornhill that center pivots are the most efficient method of irrigation, she says that cultural practices throughout the season give a grower a chance to produce strong plants and optimize the number of roots. That means regular irrigation as well as good pest management, with about 1 inch of water per week in lieu of rain. Growers who have a furrow-irrigated crop must be conscientious with timing and monitoring of weather patterns.

The harvest is another time to be efficient, Thornhill says. Sweet potatoes are machine-harvested, but because they are a root and not a tuber, they require a lot of hand labor before they hit the shed. He needs about 145 people, and begins digging in August to find his earliest fields so he can begin harvest as soon as possible. He has a trailer running alongside the harvester so potatoes can be taken into the shed immediately. He has storage space for 325,000 bushels of potatoes, with 220,000 bushels of storage being climate-controlled.

"I’m hoping someday that somebody will come up with a means of bulk harvesting sweet potatoes," he says. He could have avoided some rainfall last year if he had been able to harvest more quickly.

One thing that would allow sweet potato growers to manage risk better would be good crop insurance, Thornhill adds. The sweet potatoes that rot in the field after a season like 2008 are not covered, even if the grower has USDA crop insurance, because the current policy disallows payout on any roots that are solid and over 1.5 inches in diameter; at that point most are. Any late rotting or sunburned potatoes are not covered by a Risk Management Agency policy.

Smith says that many Louisiana producers and organizations are working to develop better crop insurance language, and she hopes the USDA will accept policy changes on issues such as the 1.5-inch exclusion.

"Crop insurance is designed to manage risk in extreme or dire situations," she says, and growers do not have sound protection against the weather. "It would be a great benefit to sweet potato producers."

Louisiana’s sweet potato crop is second only to North Carolina’s and Mississippi’s. "It is the most expensive row crop produced in Louisiana," she says, at about $3,000 per acre through harvest. Acreage this year will be from 15,000 to 16,000.

"There’s the potential for a lot of growth," Smith notes. There are some promising value-added products being created from processed sweet potatoes, including fries, canned products, chips, dehydrated flakes, juices, baby food and pet food. The Evangeline adds more potential because of the sweetness of the variety.

As for Thornhill, he’s watching the hurricane predictions avidly and hoping for a light storm season. For the long term, he is positive. He cites an encouraging export business to Europe, new products like sweet potato fries and the recovery of a sluggish economy as reasons to keep producing this crop.

Don Dale is a freelance writer and a frequent contributor. He resides in Altadena, Calif.