This PGR Is a Benefit to Blackberry Crops
April 2, 2022 Prohexadione Calcium (P-Ca) effectively and consistently reduces primocane height and internode length in blackberry, according to research conducted by North Carolina State University Assistant Professor Tom Kon.
Speaking at the annual conference of the North American Raspberry and Blackberry Association, Kon said there is a utility — in some settings — for a plant growth regulator (PGR) such as P-Ca.
“Certainly, we have what seems to be a reliable growth retardant for blackberries,” Kon says. “It may not be for the field, but I would be open to anyone’s suggestions or ideas as to where this might fit. Whether it’s in controlled environments and high tunnels, I really think that there has to be a fit somewhere for a tool like this.”
P-Ca is a gibberellin biosynthesis inhibitor used in several different cropping systems, including apple, an area in which Kon has conducted much of his research the last decade. The dose-dependent product is marketed under several brand names, including Apogee (BASF) and Kudos (Fine Americas), although none is presently registered for use in blackberry.
A 2009 potted study concluded that P-Ca was an effective growth retardant of primocane-fruiting red raspberry, although flower numbers were negatively impacted. In 2017 a Serbian study on two cultivars of floricane-fruiting blackberry found that P-Ca reduced internode length by 42% to 55% while showing increases in the number of lateral branches (13% to 24%), yield (21% to 27%), and fruit weight (8% to 19%).
Since 2018 Kon and researchers in North Carolina, South Carolina, and Arkansas have conducted four trials, including three multi-year studies. With one exception, they observed significant reduction in cane height, suggesting that the product is a very effective growth retardant in blackberry.
However, other significant responses were not as favorable. Two of the studies showed a reduction in lateral branch number. Two studies also resulted in the reduction of fruit size and yield.
“All of these treatments actually exceeded what we would consider as a grower standard, which would be tipping twice, managing primocane heights during the dormant season, and on average we had a yield of about 12.6 kilograms in a five-plant plot,” Kon says. “But this reduction in yield is somewhat concerning.
“What really needs to be untangled still is why we’re observing that, and could we offset that by looking at alternate timings. We need to understand if this specific PGR is impacting fruit set specifically, or if it is reducing flower bud development in blackberry in the Southeastern U.S.”
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