In most cases, the swelling stops rootlet growth and the infested portion eventually dies. These tuberosities may also decay, further weakening the vine. Root injuries impair the absorption of nutrients and water, causing a decline in vine vigor and productivity. Decomposition of roots is also hastened by secondary infection by fungi and by the feeding of other insects and mites. The severity of the infestation may differ because of variety, vine age and vigor, soil condition, and drainage.
Vigorous vines resist phylloxera attack better than do weak plants.
Differences in vigor can be due to site differences, but also varietal differences. Infested vines live longer in fertile, deep, well-drained soil than in shallow soil or soil with poor drainage. Vines growing in heavy, shallow soils appear to succumb to the infestation most rapidly. Fine-textured soils, such as clay, are generally more favorable to infestation than light sandy soils, which appear to be almost immune to phylloxera. Heavier soils contract and crack when drying, and these openings allow the insect to crawl to and infest root systems.