Southern sweet potatoes star in California trials
Byline: Dan Bryant
Beauregard sweet potatoes from North Carolina and Louisiana scored high in 2003 varietal trials at Livingston, according to Scott Stoddard, Merced County farm advisor.
“The goal of these trials is to find a Beauregard variety that has the yield and color of our California Beauregard with more nematode resistance and more flavor,” Stoddard told growers at a recent meeting in Merced.
The evaluations are part of the annual National Sweetpotato Collaborators Trials and measured the out-of-state materials against standard California varieties.
Beauregard, released in 1987, is the “newest” variety grown in California and was adopted because of a high percentage of U.S. No. 1 roots, or those 2 to 3.5 inches in diameter, 3 to 9 inches in length, with good shape and no defects. However, it has no nematode resistance and also suffers from losses from to russet-crack virus.
The highest count of No.1s in the 2003 trials was 772, 40-pound boxes per acre from B14 obtained from North Carolina. Its total marketable yield (TMY, or the combination of No. 1s, canners, and jumbos) was 1,497 boxes per acre.
B63, the original Beauregard from Louisiana, produced the highest TMY, 1,671 boxes per acre, and 768 boxes of No.1s. Other Beauregards from North Carolina performed in similar fashion.
MS 152, a variety from Mississippi with improved nematode resistance, produced 720 boxes of No. 1s and a TMY of 1,348 boxes. Stoddard said although it had a slow start, it has been promising in recent trials and made desirable, smooth skinned potatoes in 2003.
Diane, a California proprietary variety developed as an improvement on Garnet, showed 685 boxes of No. 1s and a TMY of 1,350 boxes. California Beauregard posted 597 boxes of No.1s and a TMY of 1,297 boxes.
Leaf curl fears
Stoddard said fears of spreading leaf curl virus to the California industry prevented him from planting more entrants from southern states in 2003. He expects to use virus-free stock of those materials in his trials this year.
Stoddard also reported on his fumigation trials outside Livingston with shanked-in fumigants Mocap, Vapam, and Telone during 2003.
“All treatments except the 2 gpa Mocap treatment significantly increased No. 1 yields and total market yield over the untreated control. The Telone and Vapam treatments had the highest marketable yields at 826 and 808 boxes per acre, respectively.”
Culls resulting from nematodes or disease, he added, were not significantly different among the treatments, although culls caused by grubs and wireworms were significantly reduced in all treatments compared to the untreated control.
Less grub damage
Plots treated with Vapam had less broadleaf weeds than those having other treatments, and treatments with Mocap alone also showed some weed suppression.
Stoddard said previous trials showed Mocap to be of little value when sprayed on the soil surface and then incorporated with a disk to 6 to 8 inches. He found that the shanked Mocap was better than no treatment. Data also indicated that a combination of Mocap and Vapam was not superior to either chemical used alone. The trials did show significantly less damage from grubs and wireworms.
In an herbicide trial near Atwater, Stoddard said he saw the best control with either Devrinol or Dacthal applied separately. The higher rate of Devrinol gave better control of redroot pigweed, and the trials indicated no advantage to using a tank mix of the two herbicides.
“Currently,” he said, “there are very few herbicides registered for sweet potatoes in California. While Devrinol and Dacthal have labels, they are not often utilized because many growers think the control is either erratic or insufficient.”
He went on to say that while the materials do not provide complete control, no more than 25 percent, even that is preferable to the nearly 75 percent weed pressure rating in untreated plots.
“Hand hoeing will not be eliminated, but it can be substantially reduced in fields where herbicides are used.”
Fumigant evaluated
As the search for alternatives to methyl bromide continues, Stoddard evaluated Midas, or iodomethane, an Arvesta Corp. fumigant in the process of being registered for use in California.
Total marketable yield was significantly increased by Midas over the untreated control plots. “The best results were obtained with Midas at the 120 pounds per acre, which was comparable to a standard application of Telone at 16 gallons per acre. Yields decreased at the higher rates.”
The liquid Midas, he explained, is less volatile than methyl bromide and has fewer air pollution issues than methyl bromide. Once within the soil, however, it does fume. It gave excellent weed control in his trials.
Fred Michaelis, Merced County agricultural biologist, reminded growers of California Department of Pesticide Regulations requirements for buffer zones between fumigation treatments and occupied structures.
The 100-foot buffer can be used every three years on a given plot, but in the interim years a 300-foot buffer must be observed.
Michaelis cited regulations for the use of Vapam in particular in flood or drip irrigation. “Remember that Vapam works on living plants, not the seed, so for the best weed control, you need to wait until the soil warms and pre-irrigate so weeds are growing.”
Avoiding contamination
To avoid the material going to neighboring crops, Vapam must not be mixed at main lines and a hydraulic brake must be used.
Odor monitoring of Vapam is a critical defense for a grower if questions about an application arise. “Vapam monitoring has to be a part of your application records to show that odor was monitored during the application,” Michaelis said.
Deb Shatley, customer agronomist for Dow AgroScience at Lincoln, was on hand to give a brief refresher course on stewardship of Telone.
“We certainly want to keep these products in your toolbox and available for your use without inordinate regulatory restraints above what we have today.
“The No. 1 objective is to keep Telone in the soil,” she said, recalling when her company was forced to withdraw, voluntarily, the California registration for Telone in April 1990 because of an air emission incident in Merced County.
Telone can be held underground by having the least possible amounts of clods plus adequate moisture to seal the surface. One advantage for sweet potatoes is the fumigant is shanked 18 inches deep.
A disk and ring-roller or cultipacker used over treated ground that is properly conditioned for sealing is ideal to disrupt the chisel traces and seal the top 4 or 5 inches of soil.
Soil must seal
“If you can poke around with a length of rebar and find the chisel trace, so can the fumigant,” Shatley said.
She warned that if a fumigant is applied where the soil does not seal, not only is the escaped material wasted but more rules and regulations are likely to be placed on use of the material.
According to statistics released by the California Department of Food and Agriculture and the National Agricultural Statistics Service, U.S. production of sweet potatoes in 2003 was 39.8 million boxes from 83,500 harvested acres.
North Carolina, with 14.7 million boxes from 42,000 acres was the leading source in the nation.
California, however, with 7.80 million boxes from 10,400 acres, or 750 boxes per acre, was by far the leading state in yields. The next highest in yields was Alabama with 475 boxes per acre.
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