1. Phylloxera

Phylloxera vastatrix was first identified in Europe in 1863. Accidentally introduced from the US, this louse destroyed two-thirds of European vineyards in the late 19th century.
In 1872, Laliman discovered that the roots of American vine species were not destroyed, and so recommended grafting V. vinifera on rootstocks of American vine species. The only other effective remedies for Phylloxera are growing vines on sandy soils or flooding the vineyard for 40 days a year.

Symptoms of Phylloxera

• Vines die (with drought symptoms) in patches that increase in size year by year.
• The roots of infected vines are covered with.
• Insects, which appear as oval yellow-brown dots surrounded by lemon-yellow eggs.
• Nodosities (whitish or yellowish growths) near the root tip.
• Tuberosities (swellings) on older roots.
• Pale green leaf galls on the under-surface of the leaves.

2. To influence the vigour of the vine

Different rootstocks have different levels of vigour and take up nutrients at different rates, and this influences the vigour of the scion. In general, high vigour plants will have:

• Greater yield
• Longer vegetative cycles
• Berries with lower sugar and higher acidity
• More susceptibility to disease

3. To confer resistance to nematodes

Nematodes (also called round, thread or eelworms) are very common in soils but are usually too small to be seen by the naked eye. Some (such as Pratylenchus and Meloidogyne species) cause damage by feeding off the roots, while others (such as Xiphinema index) transmit virus diseases. Rootstocks have differing susceptibilities to nematodes.