Vigor – it’s something pear growers constantly struggle with. Bending and tying branches, planting higher-density orchards, altering canopy architecture – all these things can help growers calm the vigor, but as Todd Einhorn, Associate Professor of Horticulture at Oregon State University says, these horticultural practices are only part of the remedy.
“It’s just extraordinarily difficult to control the vigor in ‘Anjou’ and we need solutions.”
Einhorn is studying the effects of plant growth regulators (PGRs) on controlling pear varieties. The vigor of young ‘Anjou’ can slow down early productivity. Two. The other popular winter varieties — ‘Bosc,’ and ‘Comice,’ are biennial bearers and ‘Comice’ in particular is a shy bearer, but still quite vigorous.
Where a PGR might be used to control vigor in ‘Anjou,’ a PGR would be needed to improve fruit-set with ‘Bosc’ and ‘Comice.’
Einhorn has studied using ReTain (Valent) to improve the fruit-set of ‘Anjou’ and shy bearers such as ‘Comice.’ The label suggests an application around bloom. However, ReTain is more effective if applied 7 to 10 days or so after bloom when ethylene production of developing fruitlets is markedly increasing. “When we wait and hold off for seven to 10 days after, we get about a 75% chance of increasing fruit-set,” he says.
Although there are times where no improvement has been seen, Einhorn says the vast improvement three-fourths of the time adequately makes up for the times when it doesn’t. He is currently developing research to understand the factors responsible for the inconsistent response.
Taking A Fresh Look
Studies on prohexadione calcium have shown some sensitivity with certain varieties such as ‘Bosc’ and ‘Bartlett.’ Einhorn says previous research with Apogee (BASF) had shown negative effects on return bloom of ‘Bosc’ and fruit size of ‘Bartlett’, and it was enough to have the label removed for pear.
Although several studies have shown Apogee’s effective shoot growth control, it can cause a 10% to 30% reduction in return bloom in ‘Anjou,’ and with a vigorous ‘Anjou,’ that reduction may not necessarily be a bad thing.
Einhorn is studying prohexadione calcium in another PGR, Kudos (Fine Americas), as a way to control ‘Anjou.’
“‘Anjou’ is extremely vigorous, in part because they don’t tend to set fruit early in their life so there’s a lot of horsepower,” he says. “We don’t have sufficient dwarfing roots to control the growth. More than any other cultivar, it needs help with controlling vigor in order to facilitate high-density
Understanding some of the data with ‘Anjou’ and Apogee, Einhorn and his team suspected that if the number of flowers were reduced with an application of prohexadione calcium, it could give the tree an increase in fruit-set efficiency for the remaining blooms.
Improving Return Bloom
For now, Einhorn says he will be examining the effect of Kudos on other varieties.
He is also studying ethephon around 45 days after bloom to improve flowering, which he says helps negate the effect ofprohexadione calcium. So, an application of prohexadione calcium could be applied to control vigor, and ethephon would assure return bloom would not be adversely affected in varieties that it may be a concern, such as ‘Anjou,’ ‘Bosc,’ and ‘Comice.’
“We’re getting a very nice effect on increasing return bloom, consistently around 20% to 30% partnering it with Kudos and when we were doing the Apogee work,” he says. “It’s essentially negated the effect of prohexadione calcium on reducing return bloom,” he says.
Ethephon products are currently not labeled for use with pear.
Einhorn says the PGR work is only a part of a larger portfolio of options for growers. He says often pear growers are reluctant to plant ‘Anjou’ in higher-density systems, simply because of how much trouble it can be to control the vigor.
Einhorn’s group is studying dwarfing rootstocks, root pruning, tighter in-row spacing, training systems, and canopy structuring — all component of the bigger picture of pear growing.
“The PGR approach is just one tool that we’re ultimately wanting to implement into a whole program for controlling vigor and improving cropping,” he says. “PGRs are just one tool to try to get out a sustainable, systematic approach to controlling vigor.