Madeline Wimmer- UMN Fruit Production Extension Educator
Images: Zestar!® is an early ripening UMN apple variety and is at a more advanced growth stage than other UMN varieties like First Kiss® (i.e., Rave®) and Honeycrisp.
As apple fruitlets continue to grow, in SE MN a number of apple varieties, like Honeycrisp and First Kiss® (i.e., Rave®), are between 8–12 mm, and Zestar!®—an earlier harvest variety—has been between 9–18 mm in size this week. This is helpful to keep in mind when considering thinning options. Note that a thinner like NAA generally becomes less effective after apples surpass 15 mm. Because chemical thinners work best with ambient temperatures around 70 F, it’s possible for some orchards to observe less thinning this year than previous years, noting the cooler temperatures that persisted after petal fall.
The University of Minnesota Horticulture Research Center (UMN HRC) reported their sustained catch for codling moth on May 12th. This date will now be used as a biofix date, or a marker to start recording degree day (DD) accumulations. Management begins when 200-250 DD have accumulated, which indicates when codling moth eggs will hatch into larvae and pose risk to developing apple fruits. For information on pest management options for codling moth, refer to the Midwest Fruit Pest Management Guide on page 34, “Apple first and second cover.”
Images: Bramley Seedling (England 1809) apple variety being trained, initially using a heading cut during dormancy to promote shoot growth, followed by shoot manipulation done this week (left image). Clothespins and similar products come in various sizes and the trunk diameter should in part determine which ones are used (right image). Image taken at The Garden Lab located in Rochester, Minnesota (Zone 5a).
Apple tree height and the number of years to bearing fruit depend largely on which rootstock an apple variety is grafted onto; keeping in mind other factors like damage from wild life or events like burying the graft union during planting, which can lead to a loss of the rootstock effects.
This past winter, the UMN Extension Fruit Program delivered a talk on pruning free-standing apple trees, which covered information on training apple trees through pruning techniques. Pruning can help with removing unwanted branches (that might be competing in size with the trunk, for example), and it can also help promote growth by using what is known as heading cuts.
A heading cut is simply one that cuts back a branch without fully removing it, whereas full removal would be a thinning cut. Heading cuts have been traditionally used to establish central-leader trains, standard and vigorous semi-dwarf apple trees (e.g., G.969 or M.7) to promote branching on young bareroot whips, to become the first scaffold branch layer. This can also be used on very young trees that have large sections on blind wood on trunks. Heading cuts generally promote growth about 12–24 inches below the cut.
Heading cuts happen during pruning, but the next step, promoting lateral growth and wider branch crotch angles can occur during the growing season. This practice is sometimes called branch manipulation, as wider branch crotch angles lead to stronger branches and slows down the branch vigor, as compared to branches with narrow crotch angles.
Branches are malleable during the first couple of growing seasons, and benefit from techniques to weigh or stake down woody branches. There is also the option to promote growth from the time young, green shoot growth emerges (see above image). This technique is fast and simple using objects like clothespins. Be careful with tender shoots when using this technique to avoid breaking shoots, and be mindful of the trunk diameter in relation to the size of your supplies.
When an apple tree is grafted onto a rootstock with a stronger dwarfing potential, there’s less requirement for branch manipulation. The trees themselves will fruit much sooner, while branches are younger and malleable, which will weigh the branches down automatically. There are even cases when young apple trees bear too much, too soon, which can lead to branch injury, breakage, or an excessively drooping branch.
Resources:
Images: Grapevines can be planted and established during their first year without having a trellis installed (left). During the second year of training, grapevine shoots can be grown out from single or double trunks to begin cordon establishment (middle); multiple branches can be grown and then selected during dormant pruning the following year. After the new canes have been selected and tied down to become cordons, the next step allows shoots to grow out to eventually become spurs (right).
Training, trellising, and determining the canopy height
Grapevines require more intensive training than other fruit crops, and they have great flexibility to adapt to various training systems and trellis designs. Training systems and trellis designs go together, in which three-dimensionally trained vines require three-dimensional trellises, for instance. Vine vigor and growth type, harvesting technique, and ergonomics (think about how high you can comfortably reach before deciding to establish 7 foot tall High Cordon vines, for example) all go into the planning and design process.
(Semi) permanent cordon establishment vs cane pruning
In addition to the grapevine training system, trellis type, and canopy height, some growers may also be thinking about whether to establish (semi) permanent cordons, or use cane pruning. In cane-pruned systems, no permanent cordons are established, but instead, the arm is replaced each year. This process works well for varieties grown in conditions where bud survival is high at the cane tips to allow for a final count of 12–15 nodes on each fruiting cane.
Establishing cordons in Upper Midwest regions has its own risk as they can accumulate winter injury, blank wood, and overall decline. This is why they are sometimes referred to as semi-permanent, because, while they are not regularly replaced, they will usually need to be replaced with a fresh cane at one or more points during its lifetime.
As a final note, it is possible to change the height of the canopy, or even training system type for already established grapevines. Although there are some limitations and it may require some added steps to adapt a trellis if converting from Vertical Shoot Positioning to High Cordon, or a three-dimensional system like Geneva Double Curtain.
Resources:
- Apples:
- Growth stage update: Fruitlets between 8-20 mm
- Training for young free-standing apple trees
- Grapes:
- Training young grapevines
Apples
Growth stage update: Fruitlets between 8–20 mm
Images: Zestar!® is an early ripening UMN apple variety and is at a more advanced growth stage than other UMN varieties like First Kiss® (i.e., Rave®) and Honeycrisp.
As apple fruitlets continue to grow, in SE MN a number of apple varieties, like Honeycrisp and First Kiss® (i.e., Rave®), are between 8–12 mm, and Zestar!®—an earlier harvest variety—has been between 9–18 mm in size this week. This is helpful to keep in mind when considering thinning options. Note that a thinner like NAA generally becomes less effective after apples surpass 15 mm. Because chemical thinners work best with ambient temperatures around 70 F, it’s possible for some orchards to observe less thinning this year than previous years, noting the cooler temperatures that persisted after petal fall.
The University of Minnesota Horticulture Research Center (UMN HRC) reported their sustained catch for codling moth on May 12th. This date will now be used as a biofix date, or a marker to start recording degree day (DD) accumulations. Management begins when 200-250 DD have accumulated, which indicates when codling moth eggs will hatch into larvae and pose risk to developing apple fruits. For information on pest management options for codling moth, refer to the Midwest Fruit Pest Management Guide on page 34, “Apple first and second cover.”
Training for young free-standing apple trees (standard and vigorous semi-dwarf trees)
Apple tree height and the number of years to bearing fruit depend largely on which rootstock an apple variety is grafted onto; keeping in mind other factors like damage from wild life or events like burying the graft union during planting, which can lead to a loss of the rootstock effects.
This past winter, the UMN Extension Fruit Program delivered a talk on pruning free-standing apple trees, which covered information on training apple trees through pruning techniques. Pruning can help with removing unwanted branches (that might be competing in size with the trunk, for example), and it can also help promote growth by using what is known as heading cuts.
A heading cut is simply one that cuts back a branch without fully removing it, whereas full removal would be a thinning cut. Heading cuts have been traditionally used to establish central-leader trains, standard and vigorous semi-dwarf apple trees (e.g., G.969 or M.7) to promote branching on young bareroot whips, to become the first scaffold branch layer. This can also be used on very young trees that have large sections on blind wood on trunks. Heading cuts generally promote growth about 12–24 inches below the cut.
Heading cuts happen during pruning, but the next step, promoting lateral growth and wider branch crotch angles can occur during the growing season. This practice is sometimes called branch manipulation, as wider branch crotch angles lead to stronger branches and slows down the branch vigor, as compared to branches with narrow crotch angles.
Branches are malleable during the first couple of growing seasons, and benefit from techniques to weigh or stake down woody branches. There is also the option to promote growth from the time young, green shoot growth emerges (see above image). This technique is fast and simple using objects like clothespins. Be careful with tender shoots when using this technique to avoid breaking shoots, and be mindful of the trunk diameter in relation to the size of your supplies.
When an apple tree is grafted onto a rootstock with a stronger dwarfing potential, there’s less requirement for branch manipulation. The trees themselves will fruit much sooner, while branches are younger and malleable, which will weigh the branches down automatically. There are even cases when young apple trees bear too much, too soon, which can lead to branch injury, breakage, or an excessively drooping branch.
Resources:
- Rootstocks for apple (Washington State University)
- Geneva apple rootstock comparison chart (Cornell University; e.g., G.41, G.935)
- Training and pruning apple trees (University of Wisconsin; information and diagrams demonstrating branch manipulation)
Grapes
Training young grapevines
Images: Grapevines can be planted and established during their first year without having a trellis installed (left). During the second year of training, grapevine shoots can be grown out from single or double trunks to begin cordon establishment (middle); multiple branches can be grown and then selected during dormant pruning the following year. After the new canes have been selected and tied down to become cordons, the next step allows shoots to grow out to eventually become spurs (right).
Training, trellising, and determining the canopy height
Grapevines require more intensive training than other fruit crops, and they have great flexibility to adapt to various training systems and trellis designs. Training systems and trellis designs go together, in which three-dimensionally trained vines require three-dimensional trellises, for instance. Vine vigor and growth type, harvesting technique, and ergonomics (think about how high you can comfortably reach before deciding to establish 7 foot tall High Cordon vines, for example) all go into the planning and design process.
(Semi) permanent cordon establishment vs cane pruning
In addition to the grapevine training system, trellis type, and canopy height, some growers may also be thinking about whether to establish (semi) permanent cordons, or use cane pruning. In cane-pruned systems, no permanent cordons are established, but instead, the arm is replaced each year. This process works well for varieties grown in conditions where bud survival is high at the cane tips to allow for a final count of 12–15 nodes on each fruiting cane.
Establishing cordons in Upper Midwest regions has its own risk as they can accumulate winter injury, blank wood, and overall decline. This is why they are sometimes referred to as semi-permanent, because, while they are not regularly replaced, they will usually need to be replaced with a fresh cane at one or more points during its lifetime.
As a final note, it is possible to change the height of the canopy, or even training system type for already established grapevines. Although there are some limitations and it may require some added steps to adapt a trellis if converting from Vertical Shoot Positioning to High Cordon, or a three-dimensional system like Geneva Double Curtain.
Resources:
Training systems for cold climate hybrid wine grapes (University of Wisconsin Extension)
Establishing cold hardy grapevines on spur-pruned high cordon system (University of Wisconsin; includes infographic showing training of vines for first three years created by Madeline Wimmer, 2016)
Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Non-credited photos in this article were either taken by Madeline Wimmer or within the UMN Extension system.
This article may be shared for educational purposes with attribution to the University of Minnesota Extension. For other uses, please contact UMN Extension for permission.
This article may be shared for educational purposes with attribution to the University of Minnesota Extension. For other uses, please contact UMN Extension for permission.
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