Grape phylloxera (Daktulosphaira vitifoliae (Fitch)) resistant grape rootstocks have prevented grape vine root damage by this insect for more than a century. However, we know that roots of these resistant vines harbor grape phylloxera populations. Study of the dynamics, distribution, and trends of these populations is important as a step toward understanding why rootstocks have remained efficacious as long as they have, and conversely, whether the presence of these root populations presages rootstock failure. Our main study block was at the Oakville Experimental Vineyard, Napa County, CA (Department of Viticulture and Enology, University of California, Davis) from June 2002 through October 2004. Digital images of 1103P and 101-14 Mgt. roots taken from clear plastic minirhizotron observation tubes were analyzed for trends in phylloxera infestations. Phylloxera infested a portion of first- and second-order roots and less frequently the coarser third-order roots. Infested roots have a shorter life span than uninfested roots. Apparently necrotic lesions on roots are associated with grape phylloxera presence. Inverted food storage bowls were used as emergence traps in this main study block as well as in other Napa, Mendocino, and Solano County locations. Grape phylloxera first instars and alates were recovered from the traps from May to October. Populations varied by root type and were highly uneven.