Technical Abstract: Cucurbit yellow stunting disorder virus (CYSDV), which is transmitted by the sweet potato whitefly (Bemisia tabaci Gennadius) biotype B, emerged in the Southwest US in 2006. CYSDV can infect diverse regional weed and crop species, some of which serve as sources for virus transmission to melon. To determine the efficiency of recently identified hosts as reservoirs, CYSDV titer in source tissue as determined by qRT-PCR was compared with transmission rates to melon and squash. Bean, buffalo gourd, and lettuce had relatively high virus titers that resulted in a significant level of transmission. London rocket and Shepherd’s purse had low levels of CYSDV and were poor sources for transmission. In efforts to identify strong sources of host plant resistance to CYSDV, field experiments were conducted in Imperial Valley, CA. Melon PI 313970 exhibited high-level resistance to CYSDV in replicated field tests. Mean plant condition ratings of PI 313970 were significantly (P0.05) better than those of the susceptible control, ‘Top Mark.’ Data from a cross with the CYSDV-resistant melon TGR-1551 indicated potential for significantly higher resistance than that exhibited by either resistance source alone. Although resistance to CYSDV may be increased with these sources combined, they must be used in combination with an active insecticide treatment program due to excessively high whitefly feeding pressure.