Watering blue palo verde (Cercidium floridum) affects berry maturation of parasitic desert mistletoe (Phoradendron californicum) during an extreme drought in the Mojave Desert

Resources available to parasites are often dependent on resources available to hosts. If a resource is limiting to parasites because it is limiting to hosts, supplementing that resource for hosts should affect parasites. Water availability is a limiting factor for plant productivity in many desert systems. We watered blue palo verde (Cercidium floridum) with desert mistletoe (Phoradendron californicum) infestations during a drought in the Mojave Desert during winter of 2002–2003. Mistletoe berries were monitored over a 19-week period on nine trees receiving no water, nine trees receiving “normal” water, and nine trees receiving 10× normal water. No differences were seen in overall berry numbers between treatments. However, berry crops on mistletoe plants parasitizing watered palo verdes matured and numbers declined faster than berry crops on control trees. There were no differences between plants watered a moderate amount and those watered a magnitude more, suggesting that berry maturation may be limited by a factor other than water in wet years, or that palo verde do not uptake significantly more water than is typically present. Future research is needed to conclusively determine factors limiting desert mistletoe berry maturation.