Dec 3, 2010Cane management in raspberries, blackberries
Pruning affects plant growth rate, fruit quantity and size, sugars, disease susceptibility, ease of harvest, and spraying efficiency. Brambles respond significantly to pruning and cane management, but these practices can be the most expensive and time-consuming part of an operation. There is no one procedure for all bramble types. Each type requires its own approach to pruning and cane management.
Primocane-fruiting raspberries produce fruit at the top of first-year canes in late summer. If allowed to overwinter, these same canes will produce fruit again in early summer of the second year. However, the quality of this early summer fruit is inferior to both the late-summer primocane crop and summer crops of floricane-fruiting types. Also, harvesting the early summer second-year crop is difficult because of interference from new primocanes. Likewise, harvesting the late summer primocane crop is difficult because the primocanes are thinner and taller when the second-year canes are allowed to grow. Most growers sacrifice the early summer second-year crop in favor of a smaller, but higher quality, late-summer primocane crop.
The smaller yield of a single late-summer primocane crop is offset by the ease of management. To prune primocane-fruiting raspberries for a single late-season crop, the canes need only be cut to the ground in early spring. New canes will grow each year and fruit in late summer; the canes will be cut early the following spring; and the cycle continues.
It is important to cut old canes as close to the ground as possible, so that buds will break from below the soil surface. If canes are not cut low enough, fruiting laterals may form on any remaining cane portion. These fruiting laterals are not healthy; they are entry sites for insects and disease pathogens. Also, any fruits that form will most likely rot, attracting pathogens and creating a source of inoculum for the late summer crop. All canes that are cut from the planting should be removed from the area and destroyed. In warm climates, pinching the primocanes (removing the growing tip) in July to stimulate growth of laterals will delay fruiting. This is sometimes done to delay harvest until after the intense heat of July. In colder climates, pinching will delay harvest until after frost under high tunnels.
The timing of cane cutting is also important. Carbohydrates move from plant leaves into the crown in autumn, and from the crown to the buds in early spring. If canes are cut before all the carbohydrates reach the crown in autumn, the new canes may not be as vigorous the following year. Canes can also be cut too late, after carbohydrates have moved into the buds. From December through February, most carbohydrates are in the crown, so this is the ideal time to cut canes.
Floricane-fruiting brambles produce fruit only from buds on second-year canes. Unlike primocane-fruiting raspberries, these canes must remain intact throughout the winter and following growing season, until the completion of harvest. Also, during second-year flowering and fruiting on floricanes, new first-year primocanes are growing. These primocanes interfere with spraying and harvesting, shade the leaves and laterals of floricanes and compete for water, since they share a single root system. This interference must be minimized to obtain a high yield of fruit each year.
Traditionally, primocanes emerge and are permitted to grow throughout the season. The following year, they become floricanes, flowering and fruiting as new primocanes. Immediately after fruiting and throughout the winter, expended floricanes may be cut at ground level and destroyed. Cutting canes early in summer loses some carbohydrates, but this loss is offset by the advantages of reduced disease inoculum and a reduction in dormant season pruning. Canes are thinned to a desired number, usually three to four per square foot. When thinning, the most vigorous canes should be selected to produce the next crop – those with good height, a large diameter and no visible symptoms of disease, insect damage or winter injury. All remaining canes are topped to a convenient height for picking.
After the first flush of growth is removed, primocanes are allowed to grow. In most states, there are no chemicals specifically labeled for suppressing emerging primocanes, so this step may have to be done by hand. A long-handled stick with a curved blade at the end can be used to rapidly remove emerging primocanes without bending.
The highest long-term yields and largest berry sizes have resulted from a combination of floricane thinning followed by suppression or removal of the first flush of emerging primocanes in late spring.
Since there is less shading and fewer demands for water, fruit size and productivity of lower laterals are increased. Primocanes of vigorous cultivars can still grow to a sufficient height for adequate fruiting the following year, even when the first flush of primocanes is suppressed.
Primocanes should not be suppressed until the planting is at least three years old. Primocanes contribute large amounts of carbohydrates to the bramble plant, and repeated suppression will reduce carbohydrate levels. Therefore, suppression should be skipped every third or fourth year to allow the planting to recover from the general reduction in vigor. Weak hills or sections of rows should not be suppressed at all. Full suppression is not recommended for black raspberries because they produce few primocanes.
Yield and quality may be increased without suppressing all the primocanes in a planting. Removal of all but four or five primocanes per linear foot of row in spring will increase yield and fruit quality in floricanes of some cultivars. This practice is preferred under conditions where complete primocane suppression is not desirable.
For this method, growers select the primocanes in late spring that will be carried into the following year for fruiting. Rejected primocanes are cut to ground level when 8 inches tall. The raspberry plant uses resources for the current fruiting canes and the remaining primocanes, rather than for many primocanes that would eventually be removed.
Primocane re-growth is ignored until the dormant season, when these short canes are removed. Advantages of this system are: (1) selected primocanes grow for an entire season instead of the partial season permitted in complete primocane suppression, (2) rejected primocanes are removed when small, succulent and easy to handle, as opposed to large and thorny, and (3) fruit size and quantity of current season is increased. The major disadvantages are: (1) primocane selection is difficult when leaves are on the plant and, (2) suppression of undesirable canes requires much labor.
— Marvin Pritts, Cornell University