October 12, 2017 - By Kevin Hecteman - In the sweet-potato center of California, Merced County, the 2017 harvest is well underway, with farmers reporting the crop may be a bit smaller, while new products continue to propel demand.
In the fields of growers such as D&S Farms and Atwater Packing Co. in Atwater, Mike Duarte said the 2017 crop "doesn't look as big" as last year's—but could be close.
"The No. 1s seem like they're a little bit better than they were last year," he said. "The jumbos are down, and the mediums are about what they were last year. I think by the end of the year, I think it's going to be pretty close to last year's stuff."
(Left) Employees harvest sweet potatoes at D&S Farms near Atwater. California farms grow about 20 percent of the sweet potatoes produced in the U.S. Farmers say this year’s crop may be slightly smaller than a year ago.
Duarte's business partner, David Souza, said the long string of hot summer days affected early-season sweet potatoes that were put in storage.
"The end of August, we started harvest to go to the storage buildings, and we couldn't keep the buildings cool," Souza said. "We had that week of 110 degrees, and our buildings were at 90, and the potatoes started growing."
Sweet potatoes start growing at 85 to 90 degrees, he explained, and humidity in the storage buildings stands at 80 percent. That allowed the potatoes to start sprouting plants; they dehydrate themselves in the process and shrink, reducing the tonnage, Souza said.
U.S. farmers harvested more than 3.2 billion pounds of sweet potatoes last year, according to the U.S. Department of Agriculture. North Carolina accounted for 54 percent of the nation's production. California ranked second, at 20 percent, with most of that coming from Merced County.
Bob Weimer, who grows sweet potatoes in Atwater and Livingston, said he aims for at least 60 percent of his crop to be No. 1s.
"If you get 60 percent, then you're probably at that 25-26 ton (per acre yield)," Weimer said. "It's a matter of irrigation, timing and what you're trying to achieve."
As with other California crops, value-added products have helped boost business.
"The sweet potato fries and the sweet potato puffs—they've probably increased our whole deal by … " Duarte started. Weimer finished the sentence for him: "20-25 percent."
"We're like any commodity," Weimer said. "The value-added part, in the last several years, whether it be almonds, or this commodity or that commodity, adding value to it has increased sales, has opened up new windows."
He added that, after sweet potato consumption per capita had declined over the decades, it's recently begun to rebound.
"A lot of that's based on everything from Oprah Winfrey to cooking shows to the Food Networks, and the value of the sweet potato in a person's diet," Weimer said, adding that the orange-fleshed varieties are popular for their fiber and beta-carotene.
As with many other farmers around the state, Duarte reported increasing trouble hiring enough people.
"We've probably got the best labor there is," he said, "but how long are we going to be able to continue?"
Harvesting machines, pulled by tractors, pull the sweet potatoes out of the ground and to a waiting crew of about 10; the riders sort the spuds according to size. Mechanizing that is proving to be a challenge, according to C. Scott Stoddard, a University of California Cooperative Extension farm advisor based in Merced.
"There are machines out there (to sort by size)," Stoddard said. "Unfortunately, they tear up the sweet potatoes. They skin them up, they bruise them. That becomes an issue of salability. They don't look as good. And it can become an issue in the storage buildings, as far as causing decay and rot and loss in storage that's well above what we want to have happen."
Along with inventing a gentler machine, researchers will need to come up with a tougher sweet potato.
"In the case of sweet potatoes, it's probably going to require a tougher outer skin," Stoddard said, adding that he has a screening trial underway in the county. "We call it a double skin, but it's actually a thick-skinned sweet potato."
Stoddard, the only UCCE advisor working with sweet potatoes, cooperates with breeding programs at Louisiana State University and North Carolina State University, seeking potential new varieties that enhance production and yield while maintaining the proper sugar and acid levels and flavor profiles.
Weimer said the LSU program tests thousands of varieties on an annual basis, of which one or two may work their way into trials.
"We bring it to California and we test it under our environment, and see how it performs," he said.
Sweet-potato farmers have not had to spend much time this year fighting off pests.
"The pressure in the field this year in the sweet-potato industry has been very mild," Weimer said. "There's been very little pressure from insects or disease."
Stoddard said Southern blight turned up in nursery stock at the beginning of the season, likely because of the cooler and wetter spring, but it wasn't an impediment to planting. He did see one unusual pest, however.
"We actually had to spray for hornworms, which is very odd," Stoddard said. "It's not a typical pest. Luckily, hornworms are very easy to manage, even in organic systems. We have a lot of organic sweet potatoes. We have very effective insecticide sprays that are organically approved."
Root-knot nematodes, however, are sweet-potato growers' chief enemy. They'll burrow into and knot up the roots, reducing the yield and rendering the crop unsalable, Stoddard said.
Due to limits on soil fumigation, he said, some growers practice dry-fallow rotation, where they "let the field just sit there and do nothing for an entire summer."
A similar practice is followed at D&S Farms, where fields will be planted two years and rested the third, with a cover crop of rye grass. The objective is to convince root-knot nematodes to move on.
(Kevin Hecteman is an assistant editor of Ag Alert. He may be contacted at firstname.lastname@example.org.)
Reprinted with permission: California Farm Bureau Federation