UC Davis scientists have found phylloxera infestation of rootstocks bred to be resistant to the louse.
The 101-14 rootstock is a riparia-rupestris cross intended for heavy clay soils (see Herrick Guide, here).
Ironically, while 101-14 was found to be best adapted to heavy clay soils, this is the type of soil the louse prefers and the type in which the infected vines are planted.
Other signs of phylloxera (illustrated in the newsletter) are leaf galling and canopy growth stunting.
The newsletter does note that more study is needed to see if fungi are contributing to the root stock’s newly-found susceptibility.
Anyone about to plant a new vineyard, may want to hold off on 101-14 root stock and choose another type.
If vines with this root stock are already in the ground and symptoms are seen, treating with systemic doses of imidacloprid (injected into irrigation or poured on the soils and watered in – see labeling for Provado or Admire) may be helpful. The same can be done as a prophylactic measure.
As phylloxera is susceptible to imidacloprid, foliar application of appropriate concentration (see package labeling) should eliminate leaf galling.
Details should be obtained from the UCD-IPM site or from a local Cooperative Extension Offices.