The winter of 2024-2025 saw average precipitation for the Merced area, with 9.66 inches of rain based on the California Irrigation Management Information System (CIMIS) weather station in Ballico (Merced County no longer has any functioning CIMIS stations). A cool spring was followed by a mild summer, with only six days at or above 100°F. This great weather led to low plant stress and excellent yields. Overall production was even better than in 2023, which was likewise a good year due to mild summer temperatures.
The Collaborators Trial results reflected the successful production year — the standard lines exceeded 1400 boxes/acre, or about 70 bins/acre (Figure 1). Several Bellevue fields exceeded 80 bins/acre.
Rains came early during harvest, with 1.5 inches of rain falling on October 13, followed by another storm in November. The mid-October storm may cause some problems for the stored crop, especially if the Diane cultivar was still in the ground. Soil temperatures at 6 inches depth dropped 4°F after that rain. The combination of the soil being both cold and wet during harvest created the potential for accelerated decay in storage.
How Did the Different Cultivars Perform?
The Murasaki and Vermillion cultivars continue to have inconsistent set and erratic production. Zero carryover from last year resulted in high prices for Murasaki in August and September. Farm advisor Scott Stoddard guesses that many fields were harvested early to take advantage of the price at the expense of yield, which means a short crop is likely in summer of 2026.
Vermillion quality and yield vary. The plants seem to set too many roots that never fully develop. That is why Stoddard continues to screen new reds, with three potential new releases in the pipeline.
The market for purple-flesh sweet potatoes continues to grow and command good prices. In the last two years, new purple-flesh cultivars have yielded well — over 35 bins/acre — in Stoddard’s trials. They are attractive, with good shape and skin color. Cultivar L-24-71p looks especially promising in its first year, with deep purple flesh and good flavor and texture. It may soon join the six purple cultivars already commercially available: Stokes, Ben Yagi, Regal Purple (USDA ARS), Purple Majesty (NCSU), Purple Splendor (NCSU) and Purple Reyne (LSU), grown on about 1000 acres total.
Diseases Remain Problematic
Despite the good growing season, certain diseases remain problematic. Fusarium root rot (putatively Fusarium oxysporum+ F. solani) mainly impacts Bellevue, though the other cultivars are not immune. Scurf — a superficial, soil-borne fungal disease — impacts Covington, but also can infect the other cultivars. Southern blight is mostly a problem in Diane in the hotbeds, but it can likewise damage any variety.
New work by UC Davis plant pathologist Cassandra Swett shows that the organism responsible for Fusarium foot rot may not be F. oxysporum at all, but rather the newly named Fusarium noneumartii, formerly lumped in with F. solani f.sp. batatas.
Fusarium foot rot first appeared as a major problem in 2022 during harvest, causing 10-20% loss on some fields harvested in October, after a September heat spell with several days above 105°F and a record high of 112°F on September 6. The roots rotted while still in the ground. No such heat conditions occurred in 2025, which makes the high incidence of this disease worrisome. No doubt it has been around for decades, but why it has suddenly become so prevalent is not known.
The reason for the increase in scurf, however, is most likely because of reduced use of clean seed these last few years. Scurf is easily transferred from cuttings to transplants, but does not live long in fields in the absence of sweet potatoes. “One year out and it’s gone,” Stoddard comments.
Suggested management practices for both Fusarium root rot and scurf include using thiabendazole (Mertect) fungicide in the hotbeds, using clean seed, cutting transplants above the soil line, managing nematodes and timely harvest — the longer the roots are in the ground the more likely they will become infected.
What is the acreage and production of sweet potatoes in California?
The USDA has revised their estimates for sweet potato production acres in California:
|
year |
acres |
|
2020 |
22,000 |
|
2021 |
21,000 |
|
2022 |
21,000 |
|
2023 |
19,000 |
|
2024 |
18,000 |
At 29.5 bins/acre average yield and 18,000 harvested acres, total production in 2024 was around 530 million pounds. USDA has not yet published estimates for 2025, but Stoddard estimates 18,000 acres at 35 bins/acre, for total production of 630 million pounds.
What’s Happening in Sweet Potato Research?
Variety Trials
The National Sweetpotato Collaborators Group trial is a variety trial that is conducted in multiple states. It provides regional information to plant breeders at Louisiana State University, North Carolina State University and USDA. The national results, shown in Figure 1, show that the yields vary widely among cultivars and over the years. Covington had the highest four-year total and Vermillion had the lowest.
The results of Stoddard’s 2025 Advanced Line Trials (ALT) in Merced, an expanded version of those conducted each year with Dave Souza, are presented in Figure 2. Notice how Beauregard yielded over 100 bins/acre, but was mostly jumbos (only 21% #1’s). Bellevue stands out as having both high yield and a high percentage of #1’s. Stoddard used greenhouse plant cuttings straight from Foundation Plant Services, which illustrates the tremendous yield increases possible when using new seed.
Fumigation and Nematicide Trials
Stoddard continued his evaluation of various nematicides in 2025 with an emphasis on placement and timing. The Salibro label, updated in 2025, prescribes different methods than the ones he has used for several years, limiting applications to pre-plant and 30 days after transplanting.
The experiments were conducted in hotbeds in 2023 but in fields in 2024. Even in fields, root knot nematode (RKN) counts were very low and remained so throughout the entire season. The field was fumigated in April, planted May 1 with Diane (RKN susceptible) and harvested September 17-19, 2025. Nimitz and Nemaclean nematicides were pre-plant incorporated one week before transplanting, while all the others were applied post-plant in May and June.
One of the Velum treatments was applied in the row by moving the tape over to the plants and then injecting. This position was chosen because Velum has low solubility and does not move well in soil, so direct placement near the plants may improve efficacy. A Velum-then-Salibro trial was also evaluated.
The nematicide results are shown in Figure 3. Overall, this was a high-yielding field with low nematode pressure. Nonetheless, yields were significantly higher in all the nematicide treatments than in the untreated control by an average of 8 bins/acre. The specific nematicides did not differ significantly from each other.
The big news is that Covington comes off patent in May. The high-yielding variety was released by NC State in 2005. — By Scott Stoddard, UCCE Farm Advisor, Merced and Madera Counties and edited by Nancy Power, PHD, Assistant Editor for California Fruit & Vegetable