Potato growers know that size, consistency and uniformity matter to the bottom line and non-marketable potatoes at harvest can chip away at profitability.
Take the Waneta potato; a good chipper variety appreciated by growers but panned by some processors due to its larger size.
In 2020, Mark VanOostrum, supply manager at WD Potato Limited, along with several potato producers launched trial plots looking at the impact gibberellic acid (GA), a naturally occurring plant growth regulator, has on tuber size and consistency.
Why it matters: A more consistent product can help on the farm and in processing plants.
Producers have been hesitant to use GA inputs because determining the correct rate for any variety is challenging, and improper application could reduce yield, marketability and create excessive sets with too-small sizing and distorted growth.
VanOostrum said it took some math skills to find the best active ingredient measurement/per hundredweight of potatoes use rate for NuFarm ProLiant, a granular fall-growth potato-labelled product, chosen for the trials.
VanOostrum said the current consensus is one gram active ingredient measurement per 1,300 hundredweight is the best application rate for Waneta.
VanOostrum ran two trials, one using a liquid application of the fall grow label rate of one gram active ingredient per 1,344 cwt., applied at 75 per cent, 100 per cent and 125 per cent and a second using an unknown but small rate of GA with Sta Dry Powder as the seed treatment carrier.
The small plot trials consisted of 20-foot plots of Waneta replicated four times and irrigated and treated like a commercial field and were evaluated on emergence, vigour, growth habit, yield and size.
VanOostrum said emergence quickly became a talking point when Waneta, known to be lazy in its growth had uniform plants emerge a week ahead of the control that doubled within days.
Data recorded at D.C. VanderZaag Farms, Lundy Farms, and Sunrise Potato Storage showed the GA-treated plots pulling well-ahead of the control within the first days with the Sunrise plot, hit 100 per cent emergence a full three days before the check.
Stem counts at 20 feet were performed numerous times and showed the control with a 1.8 per cent, 1.3 per cent, and 2.1 per cent stem-to-plant ratio in the D.C. VanderZaag Farms, Lundy and Sunrise plots. Conversely, the GA plants hit 2.1 per cent, 1.8 per cent and 3.8 per cent stem-to-plant ratio, pushing past the Waneta one-stem reputation.
VanOostrum said the GA-treated varieties hit 30 to 41 per cent emergence with uniform plants at four days, against the control with four per cent. The plants with higher GA also logged a significant increase in tubers with 3.8 potatoes per pound compared to 3.4 potatoes per pound for control.
“The sweet spot is around three and a half — that’s a kind of average run of potatoes that would fit in most size bags,” said VanOostrum. “The higher the number, the more tubers per pound, the more interesting it is for the small bag business.”
The Sta-Dry powdered GA treatment trial saw similar trends for Waneta providing a fast and uniform emergency of 71 per cent at four days and a 7.9 per cent increase in set, compared to a 48 per cent emergence and 6.8 per cent set increase for the control. VanOostrum said the GA-treated plot potatoes per pound were much smaller at 389 cwt. per acre compared to control at 449 cwt. per acre.
VanOostrum suspects some of the variety is attributable to the unknown GA application rate, unlike the finite measurements with the liquid GA plot applications.
“We had more tubers, but they were definitely smaller (but) we just couldn’t get the size that we wanted,” VanOostrum said, adding he doesn’t recommend applying GA in a powder because it’s less effective.
In the August pre-harvest digs, the GA-treated plants had more tubers at an above three-size category, achieving the desired set and size goals, but some yields were lower, said VanOostrum.
Considering Waneta usually produces four to five-inch tubers, he was impressed the potatoes were under four inches.
During field sugar testing on Aug. 25, the GA plots provided slightly lower sucrose levels of .575 compared to the control at .637 and appeared to be 10 days ahead in maturity all season.
To check against natural variability, they repeated the test on Sept. 21 in the Lundy plot. Again it showed the GA-treated tubers with a .284 sucrose and .004 glucose to the .340 and .004 average, respectively.
“We know having low sucrose is important for long-term chip-ability, and we do know that the sugars have been erratic with Waneta,” said VanOostrum. This is “partially because of the different ages of the potato.”
GA application could be a game-changer for chipping if it can reduce the seeding rate and improve the marketable yield of high-performing but bigger-size potato-producing varieties.
“We see significant expansion of GA this year, not only with Waneta but with some other varieties,” he said.
“You don’t have to buy (GA) come and see us we’ve got enough to do one million hundredweight,” VanOostrum said. “If you’re just looking for a trial, we’d be more than happy to share some.”