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Looking for sweet potato `home run'

Louisiana's Macon Ridge station home to foundation seed program Sometime in ancient history, wind-blown, loessial soil deposits accumulated along Louisiana's Macon Ridge. More recently, someone planted a seed and discovered the usually acidic, shallow topsoil is a fantastic medium for growing sweet potatoes.

So fantastic, in fact, that the only land-grant sweet potato research station in the country was established on the ridge - just south of Winnsboro - in 1949.

"It was located on the Macon Ridge because they wanted to have a foundation seed program outside the sweet potato weevil-infested areas of south Louisiana. The winters are normally cold enough in north Louisiana that weevils don't overwinter well here," says station director Mike Cannon.

The foundation seed program was established with the station's opening. Work then branched out into cultural practices studies, cooperative research in breeding, plant pathology, entomology, soil, weed control, plant nutrition, and other aspects of sweet potato production.

"We work closely with other LSU AgCenter scientists housed at the Baton Rouge campus. Our two primary goals are foundation seed production and cultural practices research. Sweet potatoes are a tropical plant. The work we do here is viewed by farmers across the South and also out in California," says Cannon.

A new potato Growing sweet potatoes is entirely different than growing most row crops. A new variety begins its life at a nursery on the LSU campus in Baton Rouge. The parents, planted at random in the nursery, bloom on a trellis and are picked over to find the qualities farmers are looking for. Among the characteristics: high yield, disease and insect resistance, and sweet flavor.

It's too expensive to pollinate by hand, thus bees are allowed to do the work.

"We don't know who the male parent is since the pollen could have come from any parent in the nursery. But we know the female parent since the resulting seed is collected from her."

The true seed that results is then saved and sent to Cannon and colleagues.

"In January, we plant the seed in our greenhouse. In late May, we harvest the plants from a given parent. By this time they have made a small storage root (sweet potato). Each root is sliced by hand and if the root flesh is orange, we save the plant. At this point, we're only concerned with the internal flesh color. We discard plants that develop white, yellow or light orange flesh."

If the seedling makes the cut, it's planted in a field infested with soil rot - a disease sweet potatoes are susceptible to. The plot used is one of the most soil rot-infested areas in the country and has greatly enhanced efforts of the breeding program to breed for resistance. Any new variety coming from the LSU AgCenter program will be soil rot-resistant, says Cannon.

"So by the end of the first year, we've screened 30,000 seedlings for orange flesh and soil rot-resistance. Out of the 30,000, we may keep 200 or 300 that have qualities we like. One plant represents wide-ranging genetics that could lead to a new variety. For that reason, we keep the storage root selections from the soil rot test together. These are stored during the winter and evaluated the next spring for their storageability. Those that didn't store well are discarded."

The first-year keepers are bedded to produce plants that are then planted in replicated tests to begin the evaluation process for yield and baking quality. By the end of the second year, researchers will have narrowed the first 200 to 300 keepers down to 10 or 15 groups felt worthy to continue testing on. Soon, those will be whittled down even further.

And there's no break. Every year, between 20,000 and 30,000 new true seed need to be put through their paces.

The home run king In 1982, the Beauregard variety started out a true seed in an insect-resistance nursery established by Larry Rolston. By 1987, it was released as a new variety. That quick turnaround was unusual. Beauregard was on a stream-lined course because it looked so good in every phase of testing, says Cannon.

"Every once in a while you hit a home run. This was the real deal."

By the time Beauregard was released, the sweet potato industry was going downhill quickly. From 34,000 acres in the mid-1970s, state acreage had dropped to less than 20,000 by the mid-1980s. The industry was floundering.

"We were trying to grow varieties that were developed by North Carolina for their sandy soils. Here, that variety - Jewel - often produced softball-shaped roots and was highly susceptible to soil rot disease. The yield was good, but the quality wasn't. What works for them, may not work for us and vice versa. Beauregard in their sandy soils produces elongated roots."

For Louisiana, though, Beauregard was a winner right out of the gate. It was obvious this was an excellent potato.

"In 1985 and 1986 we had numerous on-farm plantings across the state of seedling 82-508 (later Beauregard). As we began to harvest the plots, it was amazing. The growers saw it and knew something special had been found. They wanted it fast because the industry was doing terribly at that time."

Cannon says Beauregard probably jumped marketable yield 50 percent. It also increased yields well over 100 bushels per acre. Currently, it's estimated that overall the sweet potato industry annually contributes $105 million to the Louisiana economy.

"The impact it had on the industry is beyond description, really. It was that dramatic and came at the most opportune time."

Virus-tested After a few years, Beauregard began to go downhill in yield and quality. To stop that trend, researchers came up with a strategy. It was found that every sweet potato plant in the country was infected with one or more virus diseases. To minimize the number and impact of those viruses, researchers came up with a technique (meristem tip culture) of growing a tissue culture resulting in essentially virus-free plants. Testing of virus-tested versus virus-infected plants showed yields of the virus-tested jumped from 30 percent to 150 percent in some tests.

With these findings, sweet potato farmers in Louisiana could stop holding their collective breath. Virus cleaning changed the way sweet potatoes had been grown for 50 years.

"To begin the foundation seed process, we take virus-tested plants out of test tubes, grow them up in a greenhouse, take cuttings and eventually take large populations and transplant them into the field. Even though Beauregard isn't what it once was, it is back to prominence. Any new variety will have to be super to beat it out."

The station There's about 320 acres on the station (with some 175 acres in cultivation). By regulation, the station can only plant sweet potatoes for foundation seed once every three years in the same field. Every year, the station normally produces about 8,000 to 10,000 bushels of foundation seed.

How are the foundation seed distributed? "We first send a letter to parish Extension agents giving them an estimate of the quantity of seed we have in storage. That letter is then sent to the parish growers. The growers tell the agents how many bushels of seed they need. The agents gather the responses and send them back to us. The average order is usually around 200 bushels of foundation seed."

A grower will take that 200 bushels, bed it separately from his normal seed and likely produce 4,000 to 6,000 bushels of second-generation virus-tested seed for the next year. The grower will then use that to plant 200 to 300 acres of sweet potatoes. One potato, depending on the variety, will give between 20 and 30 sprouts, says Cannon.

"We're currently up to about 25,000 acres of sweet potatoes in the state. The heat and drought this year will have a serious impact on production. I would estimate that state yields will be near or below average - not a bumper crop by any means. The average total yield for the state is around 325 bushels per acre. Normally, around 50 percent to 60 percent of the yield will be sold for fresh market and the remainder goes for processing. The `field-graded' number ones are taken to a packing shed and either stored for later packing or they're washed, graded, packed and shipped to market."

The growing season The crop is propagated vegetatively. Bedding takes place from mid-February to mid-March. Transplanting begins in south Louisiana in mid-April. Further north, transplanting usually begins in late April or early May.

"Harvesting further south begins in mid-July. Here, we start a month later. Harvest continues through to Thanksgiving, sometimes into December. A one-row digger can harvest about an acre per day. We do have some two-row and four-row harvesters that will cover considerably more ground in a day. Even so, it's not a quick process like most row crops."

Grubs are trouble for sweet potatoes. You don't know they're there until you harvest, says Cannon.

"The problem is the preplant insecticides like Lorsban and Mocap will last about 35 to 40 days. They do a good job in controlling overwintering grubs, but don't persist long enough in the soil to give season-long control. It takes about a month for a transplant to develop a storage root. By that time, the preplant insecticides have run out and we have no lay-by material labeled for sweet potatoes to extend control of these soilborne insects. Thus the crop is most vulnerable as the storage roots are sizing and developing into the marketable sweet potato."

In the entire United States there are only around 90,000 acres of sweet potatoes grown. Chemical companies don't want to develop products just for sweet potatoes - it's just not profitable.

"We piggy-back. If a product looks good on another crop, we'll try it out on sweet potatoes.

"Our strategy on controlling some of the soil insects like the cucumber beetle, white fringe beetle and flea beetle is to spray and control adults before they lay eggs that will eventually develop into larvae that feed on storage roots. That works for those kind of insects, but the grub worms are tough to deal with."

"We're looking at tillage in research. No-till has worked well as far as production and quality. Yield and quality of sweet potatoes transplanted into wheat stubble worked well. But since we aren't disturbing the ground, no preplant insecticide can be applied. Grubs are a problem with crops that have a lot of feeder roots like wheat.

"The final result was that we increased our yield by 20 percent through conservation tillage. But using that system triggered more grub damage," says Cannon.

Avoyelles Parish, La., sweet potato producers are suffering from the effects of prolonged drought and insect problems that are drastically reducing their crops.

Even more, experts say the problems could become worse and possibly spread if farmers don't follow recommendations this year to reduce insect populations.

"The prolonged drought, mild winters and the failure of some farmers to follow recommended cultural practices last year are causing severe production problems for sweet potato producers in Avoyelles Parish," said Earnest Freeman of the LSU AgCenter.

Professionals generally agree the drought, high temperatures and pest problems worked together to decimate this year's crop.

"I'm only harvesting about one-half the potatoes this year as compared to the last few years," said Carl Ducote, a farmer near Bunkie, La. Ducote said he usually digs 350 bushels of potatoes per acre in a good year, but this year he is getting fewer than 200 bushels.

"The sweet potatoes are smaller, and there are not as many of them to go to market this year," Freeman added.

Louisiana is second only to North Carolina in supplying the sweet potatoes to the country. Sweet potatoes also are the largest agronomic crop grown in Avoyelles Parish - with a total return to the local economy of more than $13 million.

The mild winters for the past several years allowed larger populations of insects to survive the winter, multiply during the growing season and attack the sweet potato crop. Among those, the sweet potato weevil was particularly severe this year and caused producers to lose both yield and profit.

"This year we have had major problems with three primary insects: sweet potato weevil, grub worms and cucumber beetle, but the worst problem is with the sweet potato weevil," Freeman said.

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