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Rootstocks

Rootstocks now available for cherries are Mazzard, Mahaleb, Colt, and the MxM series. Mazzard is a sweet cherry seedling adaptable to both sweet and tart cherries. It is tolerant of heavier soils. Trees on Mazzard are larger than the same cultivar on Mahaleb. Mahaleb is the standard rootstock for tart cherries because it is slightly dwarfing, more tolerant of drought and cold, and more precocious than Mazzard. It is not, however, compatible with all sweet cherry cultivars.

Colt, a recently introduced rootstock from England, is reported to be precocious and semidwarfing. A size reduction of 25 percent was reported over standard rootstocks for cherries. However, trees on Colt have been found to be drought sensitive and not cold hardy. Therefore, Colt is recommended only for warmer areas with irrigation.

The MxM series was developed in Oregon by Lyle Brooks from crosses made between Mahaleb and Mazzard. Currently MxM 2, MxM 60, and MxM 39 are available commercially. None provide any dwarfing capabilities. As a group all are reported to have good resistance to most common root rot problems.

MxM 2. More vigorous than Mazzard but more precocious. May perform better in weaker or sandier soils. Tolerant to both Prunus necrotic ringspot and prune dwarf viruses. Also reported to have good field tolerance to bacterial canker of cherry (Pseudomonas syringae).

MxM 39: Supposed to be the most dwarfing, producing a tree about 80 percent the size of Mazzard. However, Pennsylvania trials have shown that it does not appear to be that much smaller in its early years.

MxM 60. Reportedly produces a tree about 90 percent the size of standard rootstocks. In Pennsylvania, Montmorency on this rootstock produces very bushy trees. MxM 60 is compatible with both sweet and tart cherries. Tolerant to both Prunus necrotic ringspot and prune dwarf viruses. Also reported to have good field tolerance to bacterial canker of cherry (Pseudomonas syringae).

New cherry rootstocks
The next few years may bring an increase in the number of rootstocks for both tart and sweet cherries. Right now, however, we are not recommending that cherry growers plant large blocks of these rootstocks until they have been thoroughly evaluated. Growers should try small plantings under their own conditions as rootstocks become available.

In 1998, an NC-140 rootstock trial was established at a commercial orchard in Franklin County and the grape research station in Erie County. The cultivars were Hedelfingen in Erie County and Montmorency in Franklin County. Rootstocks in the trial include Edabriz, Gi 195-20, Gi 209-1, Gi 473-10, Gisela 5, Gisela 6, Gisela 7, Weiroot 10, Weiroot 13, Weiroot 158, Weiroot 53, Weiroot 72, and P. avium and P. mahaleb as controls.

The Gisela series of rootstocks was developed in Germany in the 1960s at Justus Leibig University in Giessen by Drs. Werner Gruppe and Hanna Schmidt. Several of the more promising selections were imported into the United States in the 1980s and included in the 1987 NC-140 planting at various locations throughout the country. From these trials four rootstocks have become commercially available: Gisela 5, Gisela 6, Gisela 7, and Gisela 12. Size control ranges from 45 to 80 percent of the size of similar cultivars on Mazzard. Initial reaction was very favorable, but in recent years there has been concern about virus susceptibility. Nevertheless, they do offer some size control. Growers should take care that the trees do not overcrop in the early years and fail to develop proper canopy size. In general, tree support is recommended for all the Gisela stocks that have been released. Below are descriptions of the four.

Gisela 5: Tested as Gi148/2, it is reportedly very precocious, producing a tree about 50 percent the size of Mazzard. The rootstock seems to induce an open canopy with wide branch angles. Trees produce few suckers.

Gisela 6: Tested as Gi 148/1, it is a precocious rootstock that produces trees about 65 to 95 percent of the size of trees on Mazzard. It is reported to induce early bloom and is tolerant of viruses. Extra care must be taken to ensure that desired shoot extension growth is maintained

Gisela 7: Tested as Gi148/8, it is reported to be about 50 percent the size of Mazzard. The rootstock produces some suckers. Support is also recommended for trees on this rootstock. Gisela 7 in recent research has shown some sensitivity to Prunus Necrotic Ringspot virus. Therefore, nematode management strategies for peaches should also be used when planting this rootstock.

Gisela 12: Tested as Gi195/2, this is a semidwarf type producing a tree about 70 percent the size of Mazzard. It is reported to have good virus resistance and does not sucker.