Grape growers in the Southern San Joaquin Valley are increasingly turning to rootstocks when planting vineyards where damaging nematode populations or phylloxera are known to be present.

Rootstocks are also used to increase or decrease the vigor of the fruiting variety. Freedom and Harmony are the most popular choices, but 1103 P (Paulsen), Salt Creek (Ramsey) and 5C (Teleki) and others are being used.

Growers have been fortunate over the years in being able to plant vineyard on sites free from phylloxera and with non-damaging populations of nematodes. This allowed the planting of vines on their own roots. However, phylloxera has become widespread along the east side of the San Joaquin Valley especially on fine texture soils (loam, fine sandy loam, clay loam and clay soils).

It is becoming more common for growers to replant vineyards, and damaging populations of nematodes are usually present. Rootstocks that are resistant to nematodes and phylloxera are used to overcome damage from present and future soil pests. Growers are also using rootstocks to invigorate low vigor fruiting varieties, such as Redglobe, and vineyards planted on sandy, low capacity soils.

There is also some interest in using low vigor rootstocks with high vigor fruiting varieties grown on fertile soil in order to reduce vine vigor.

Grafting effects

Grafting a variety onto a rootstock does not change the nature of the variety but may alter such characteristics as berry size, fruit color, time of ripening — just as different soil types will affect these characteristics. It is important to select a rootstock that is appropriate for the fruiting variety's growth and fruiting characteristics.

The vigor of the rootstock should compliment the fruiting variety, soil capability, and trellis design. Freedom, 039-16, and Salt Creek are high vigor stalks. Expansive trellis systems (open gable, overhead, wide T trellis) can exploit high vigor while a restrictive trellis can encourage vegetative growth at the expense of fruit production.

Shading that occurs when a canopy is hay-stacked atop a restrictive trellis reduces bud fruitfulness and yield. This can be a problem with Thompson Seedless, Fantasy Seedless, Crimson Seedless, Princess, and other varieties that require high light for flower cluster differentiation.

The rootstocks 101-14 Mgt and 1616C are medium to low vigor stocks. They are popular with wine grape growers in cool climate districts and used to reduce the vigor of the fruiting variety. They have potential for this use in the San Joaquin Valley.

Rootstocks have a pronounced influence on the mineral nutrition of the fruiting variety. Vigorous stocks tend to reduce zinc levels but increase the uptake of potassium. The nitrogen content of the fruiting variety increases with Freedom and 039-16 but is reduced with Harmony and 1616C.

Mineral tolerance

The effect of rootstock on the mineral nutrition of the scion must be considered when developing fertilization programs.

Rootstocks will vary in their tolerance to salinity and lime. The rootstock 1103 Paulsen has excellent salinity tolerance and excludes chloride. Freedom, Harmony, Salt Creek and 1103 Paulson all have some tolerance to high lime soils.

Rootstocks vary in their nematode and phylloxera resistance. Freedom, Harmony, Salt Creek, Schwarzmann and 1616C have good general nematode resistance, but they vary somewhat with their resistance to Root knot and Dagger (Xiphinema index) nematodes. The rootstock 039-16 is tolerant of fanleaf virus because it is highly resistant to Dagger nematode, which vectors the virus.

Teleki 5C, Salt Creek, 1103 Paulsen, Schwarzmann, and 039-16 are quite resistant to phylloxera while Freedom and Harmony have low to medium phylloxera resistance. The degree of long-term phylloxera resistance is questionable for Freedom and Harmony due to the unknown Vitis vinifera parentage of these rootstocks.