Rootstock selection changes Concord vine size and yield
Nearly all of the 30,000 acres of Concord grown in the Lake Erie AVA are planted on their own roots. The common practice for just about any other variety in the US is to graft grapevine scions to a rootstock. Could Concord benefit from a different root system?
The primary function of currently used rootstocks is to provide below ground pest resistance from grape phylloxera and parasitic nematodes. This becomes a bigger deal with V. vinifera varieties or hybrids with substantial V. vinifera parentage because phylloxera damage can be severe enough to kill the vines. Concord is a V. labrusca variety native to eastern North America and presumably co-evolved with phylloxera. It turns out that Concord is “tollerant” but not fully “resistant”to phylloxera which means that Concord roots are damaged by phylloxera but not so much that it kills the vine. For the most part, improving vineyard water and nutrient availability is enough overcome Concord phylloxera damage to have productive vines.
That leads us to the question…How much better might Concord do if grafted to resistant rootstocks? Nelson Shaulis from Cornell and Lloyd Lider from UC Davis looked at this back in the 1950s by comparing own-rooted Concord and Concord grafted to 3309C rootstock. Dr. Shaulis did show that vine size and yield could be increased with 3309C rootstock and considered it useful for GDC training where it is important to maintain large vine size.
The secondary function of rootstocks is to impart a desired level of vine vegetative growth…and this may change under different soil conditions. One of the goals of a vineyard manager is to match the right rootstock with the right soil type to give a desired level of vine growth and fruit quality. This is something which needs to be investigated at the local vineyard level.
From 2004-2007, Dr. Peter Cousins and I conducted a trial in the Lake Erie region comparing the growth and yield of own-rooted Concord against Concord grafted to eight different rootstocks. The trial was repeated on two common soil types in the region: a well-drained gravel-loam soil and a somewhat poorly drained clay-loam soil.
The figure shows the vine size – yield response by soil type and rootstock selection. This again reinforces the the fact that larger vine size (or vine capacity) has greater yield potential.
The gravel-loam soil had larger vine size and yield than the clay-loam soil. In general, grape roots do not grow well in poorly drained soils leading to lower performance. Draining wet soils can mitigate this situation.
On the clay-loam soil in our rootstock trial, own-rooted vines were the most tolerant of the wet soil conditions and outperformed the other rootstocks. Out of the rootstock group, 420A and SO4 performed better than the other rootsocks.
On the gravel-loam soil in our trial, own-rooted Concord was at the back of the pack with other “low-vigor” stocks, such as 44-53M and Riparia Gloire. Vine size and yield could be increased with the other rootstocks and SO4 had the highest vine size and yield.
